完美解决关于禁止ViewPager预加载的相关问题

我最近上班又遇到一个小难题了，就是如题所述：ViewPager预加载的问题。相信用过ViewPager的人大抵都有遇到过这种情况，网上的解决办法也就那么几个，终于在我自己不断试验之下，完美解决了（禁止了）ViewPager的预加载。

好了，首先来说明一下，什么是ViewPager的预加载：ViewPager有一个 “预加载”的机制，默认会把ViewPager当前位置的左右相邻页面预先初始化（俗称的预加载），它的默认值是 1，这样做的好处就是ViewPager左右滑动会更加流畅。

可是我的情况很特殊，因为我 5 个Fragment里有一个Fragment是有SurfaceView的，这样造成的问题就是，我ViewPager滑动到其相邻页面时，含有SurfaceView的页面就会被预先初始化，然后SurfaceView就开始预览了，只是我们看不到而已。同样的，当我们从含有SurfaceView的页面滑倒其相邻的页面时，SurfaceView并不会回调其surfaceDestory方法。于是这给我造成了极大的困扰。

ok，下面言归正传，到底该怎么禁止ViewPager的这个预加载问题呢？

方案1：网上大多数说法是 懒加载，即让ViewPager预加载初始化UI，而具体一些数据，网络访问请求等延迟加载。这是靠Fragment里有一个setUserVisibleHint(boolean isVisibleToUser)的方法，我们可以在这个方法里做判断，当其True可见时（即切换到某一个具体Fragment）时才去加载数据，这样可以省流量。但这里并不满足我的需求，因为某一个Fragment并不会在ViewPager滑动到其相邻的Fragment时销毁。这个只可以解决部分人问题。

首先我们来深入了解下ViewPager的预加载机制：

上文提到过，ViewPager默认预加载的数量是1，这一点我们可以在ViewPager源码里看到。

DEFAULT_OFFSCREEN_PAGES 这里就定义了默认值是1， 所以网上 有种解决方案 说调用ViewPager的setOffscreenPageLimit(int limit)，来设置ViewPager预加载的数量，但是这里很明确的告诉你，这种方案是不可行的，如下图ViewPager源码：

我们可以看到，如果你调用该方法传进来的值小于1是无效的，会被强行的拽回1。而且DEFAULT_OFFSCREEN_PAGES 这个值是private的，子类继承ViewPager也是不可见的。

方案2：然后网上有第二种说法，自定义一个ViewPager，把原生ViewPager全拷过来，修改这个DEFAULT_OFFSCREEN_PAGES 值为0。对，就是这种解决方案！！但是！！

但是！！！但是什么呢？但是我试过，没用。为什么呢？接下来就是本文的重点了。

因为现在Android都6.0了，版本都老高了，其实android虽然每个版本都有v4包，但是这些v4包是有差异的。这就造成高版本v4包里的ViewPager，即使你Copy它，将其DEFAULT_OFFSCREEN_PAGES的值改为0，还是不起作用的，其中的逻辑变了。具体哪里变了导致无效我也没有继续研究了，毕竟公司不会花时间让我研究这些啊。偷笑

完美解决方案：ok，所以关于禁止ViewPager预加载的完美解决方案就是，使用低版本v4包里的ViewPager，完全copy一份，将其中的DEFAULT_OFFSCREEN_PAGES值改为0即可。博主亲测 api 14 即 Android 4.0的v4包里ViewPager 有效。

当然，谷歌既然有这么一种ViewPager的机制肯定有它的道理，所以一般还是预加载的好。

最后，因为低版本的源码越来越少的人会去下载，这里直接把这个禁止了预加载的ViewPager贴上来，需要的人就拿去吧。copy就能用了。

package com.plumcot.usb.view;     import android.content.Context; import android.database.DataSetObserver; import android.graphics.canvas; import android.graphics.Rect; import android.graphics.drawable.Drawable; import android.os.Parcel; import android.os.Parcelable; import android.os.SystemClock; import android.support.v4.os.ParcelableCompat; import android.support.v4.os.ParcelableCompatCreatorCallbacks; import android.support.v4.view.KeyEventCompat; import android.support.v4.view.MotionEventCompat; import android.support.v4.view.PagerAdapter; import android.support.v4.view.VelocityTrackerCompat; import android.support.v4.view.ViewCompat; import android.support.v4.view.ViewConfigurationCompat; import android.support.v4.widget.EdgeEffectCompat; import android.util.AttributeSet; import android.util.Log; import android.view.FocusFinder; import android.view.KeyEvent; import android.view.MotionEvent; import android.view.SoundEffectConstants; import android.view.VelocityTracker; import android.view.View; import android.view.ViewConfiguration; import android.view.ViewGroup; import android.view.ViewParent; import android.view.accessibility.AccessibilityEvent; import android.view.animation.Interpolator; import android.widget.Scroller;  import java.util.ArrayList; import java.util.Collections; import java.util.Comparator;   public class NoPreloadViewPager extends ViewGroup {   private static final String TAG = "<span >NoPreLoadViewPager</span>";   private static final boolean DEBUG = false;    private static final boolean USE_CACHE = false;    private static final int DEFAULT_OFFSCREEN_PAGES = 0;//默认是1   private static final int MAX_SETTLE_DURATION = 600; // ms    static class ItemInfo {     Object object;     int position;     boolean scrolling;   }    private static final Comparator<ItemInfo> COMPARATOR = new Comparator<ItemInfo>(){     @Override     public int compare(ItemInfo lhs, ItemInfo rhs) {       return lhs.position - rhs.position;     }};    private static final Interpolator sInterpolator = new Interpolator() {     public float getInterpolation(float t) {       // _o(t) = t * t * ((tension + 1) * t + tension)       // o(t) = _o(t - 1) + 1       t -= 1.0f;       return t * t * t + 1.0f;     }   };    private final ArrayList<ItemInfo> mItems = new ArrayList<ItemInfo>();    private PagerAdapter mAdapter;   private int mCurItem;  // Index of currently displayed page.   private int mRestoredCurItem = -1;   private Parcelable mRestoredAdapterState = null;   private ClassLoader mRestoredClassLoader = null;   private Scroller mScroller;   private PagerObserver mObserver;    private int mPageMargin;   private Drawable mMarginDrawable;    private int mChildWidthMeasureSpec;   private int mChildHeightMeasureSpec;   private boolean mInLayout;    private boolean mScrollinGCacheEnabled;    private boolean mPopulatePending;   private boolean mScrolling;   private int mOffscreenPageLimit = DEFAULT_OFFSCREEN_PAGES;    private boolean mIsBeingDragged;   private boolean mIsUnableToDrag;   private int mTouchSlop;   private float mInitialMotionX;      private float mLastMotionX;   private float mLastMotionY;      private int MactivePointerId = INVALID_POINTER;      private static final int INVALID_POINTER = -1;       private VelocityTracker mVelocityTracker;   private int mMinimumVelocity;   private int mMaximumVelocity;   private float mBaseLineFlingVelocity;   private float mFlingVelocityInfluence;    private boolean mFakeDragging;   private long mFakeDragBeginTime;    private EdgeEffectCompat mLeftEdge;   private EdgeEffectCompat mRightEdge;    private boolean mFirstLayout = true;    private OnPageChangeListener mOnPageChangeListener;       public static final int SCROLL_STATE_IDLE = 0;       public static final int SCROLL_STATE_DRAGGING = 1;       public static final int SCROLL_STATE_SETTLING = 2;    private int mScrollState = SCROLL_STATE_IDLE;       public interface OnPageChangeListener {           public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels);           public void onPageSelected(int position);           public void onPageScrollStateChanged(int state);   }       public static class SimpleOnPageChangeListener implements OnPageChangeListener {     @Override     public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {       // This space for rent     }      @Override     public void onPageSelected(int position) {       // This space for rent     }      @Override     public void onPageScrollStateChanged(int state) {       // This space for rent     }   }    public NoPreloadViewPager(Context context) {     super(context);     initViewPager();   }    public NoPreloadViewPager(Context context, AttributeSet attrs) {     super(context, attrs);     initViewPager();   }    void initViewPager() {     setWillNotDraw(false);     setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);     setFocusable(true);     final Context context = getContext();     mScroller = new Scroller(context, sInterpolator);     final ViewConfiguration configuration = ViewConfiguration.get(context);     mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);     mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();     mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();     mLeftEdge = new EdgeEffectCompat(context);     mRightEdge = new EdgeEffectCompat(context);      float density = context.getResources().getDisplayMetrics().density;     mBaseLineFlingVelocity = 2500.0f * density;     mFlingVelocityInfluence = 0.4f;   }    private void setScrollState(int newState) {     if (mScrollState == newState) {       return;     }      mScrollState = newState;     if (mOnPageChangeListener != null) {       mOnPageChangeListener.onPageScrollStateChanged(newState);     }   }    public void setAdapter(PagerAdapter adapter) {     if (mAdapter != null) { //      mAdapter.unreGISterDataSetObserver(mObserver);       mAdapter.startUpdate(this);       for (int i = 0; i < mItems.size(); i++) {         final ItemInfo ii = mItems.get(i);         mAdapter.destroyItem(this, ii.position, ii.object);       }       mAdapter.finishUpdate(this);       mItems.clear();       removeAllViews();       mCurItem = 0;       scrollTo(0, 0);     }      mAdapter = adapter;      if (mAdapter != null) {       if (mObserver == null) {         mObserver = new PagerObserver();       } //      mAdapter.registerDataSetObserver(mObserver);       mPopulatePending = false;       if (mRestoredCurItem >= 0) {         mAdapter.restoreState(mRestoredAdapterState, mRestoredClassLoader);         setCurrentItemInternal(mRestoredCurItem, false, true);         mRestoredCurItem = -1;         mRestoredAdapterState = null;         mRestoredClassLoader = null;       } else {         populate();       }     }   }    public PagerAdapter getAdapter() {     return mAdapter;   }       public void setCurrentItem(int item) {     mPopulatePending = false;     setCurrentItemInternal(item, !mFirstLayout, false);   }       public void setCurrentItem(int item, boolean smoothScroll) {     mPopulatePending = false;     setCurrentItemInternal(item, smoothScroll, false);   }    public int getCurrentItem() {     return mCurItem;   }    void setCurrentItemInternal(int item, boolean smoothScroll, boolean always) {     setCurrentItemInternal(item, smoothScroll, always, 0);   }    void setCurrentItemInternal(int item, boolean smoothScroll, boolean always, int velocity) {     if (mAdapter == null || mAdapter.getCount() <= 0) {       setScrollingCacheEnabled(false);       return;     }     if (!always && mCurItem == item && mItems.size() != 0) {       setScrollingCacheEnabled(false);       return;     }     if (item < 0) {       item = 0;     } else if (item >= mAdapter.getCount()) {       item = mAdapter.getCount() - 1;     }     final int pageLimit = mOffscreenPageLimit;     if (item > (mCurItem + pageLimit) || item < (mCurItem - pageLimit)) {       // We are doing a jump by more than one page. To avoid       // glitches, we want to keep all current pages in the view       // until the scroll ends.       for (int i=0; i<mItems.size(); i++) {         mItems.get(i).scrolling = true;       }     }      final boolean dispatchSelected = mCurItem != item;     mCurItem = item;     populate();     final int destX = (getWidth() + mPageMargin) * item;     if (smoothScroll) {       smoothScrollTo(destX, 0, velocity);       if (dispatchSelected && mOnPageChangeListener != null) {         mOnPageChangeListener.onPageSelected(item);       }     } else {       if (dispatchSelected && mOnPageChangeListener != null) {         mOnPageChangeListener.onPageSelected(item);       }       completeScroll();       scrollTo(destX, 0);     }   }    public void setOnPageChangeListener(OnPageChangeListener listener) {     mOnPageChangeListener = listener;   }       public int getOffscreenPageLimit() {     return mOffscreenPageLimit;   }       public void setOffscreenPageLimit(int limit) {     if (limit < DEFAULT_OFFSCREEN_PAGES) {       Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to " +           DEFAULT_OFFSCREEN_PAGES);       limit = DEFAULT_OFFSCREEN_PAGES;     }     if (limit != mOffscreenPageLimit) {       mOffscreenPageLimit = limit;       populate();     }   }       public void setPageMargin(int marginPixels) {     final int oldMargin = mPageMargin;     mPageMargin = marginPixels;      final int width = getWidth();     recomputeScrollPosition(width, width, marginPixels, oldMargin);      requestLayout();   }       public int getPageMargin() {     return mPageMargin;   }       public void setPageMarginDrawable(Drawable d) {     mMarginDrawable = d;     if (d != null) refreshDrawableState();     setWillNotDraw(d == null);     invalidate();   }       public void setPageMarginDrawable(int resId) {     setPageMarginDrawable(getContext().getResources().getDrawable(resId));   }    @Override   protected boolean verifyDrawable(Drawable who) {     return super.verifyDrawable(who) || who == mMarginDrawable;   }    @Override   protected void drawableStateChanged() {     super.drawableStateChanged();     final Drawable d = mMarginDrawable;     if (d != null && d.isStateful()) {       d.setState(getDrawableState());     }   }    // We want the duration of the page snap animation to be influenced by the distance that   // the screen has to travel, however, we don't want this duration to be effected in a   // purely linear fashion. Instead, we use this method to moderate the effect that the distance   // of travel has on the overall snap duration.   float distanceInfluenceForSnapDuration(float f) {     f -= 0.5f; // center the values about 0.     f *= 0.3f * Math.PI / 2.0f;     return (float) Math.sin(f);   }       void smoothScrollTo(int x, int y) {     smoothScrollTo(x, y, 0);   }       void smoothScrollTo(int x, int y, int velocity) {     if (getChildCount() == 0) {       // Nothing to do.       setScrollingCacheEnabled(false);       return;     }     int sx = getScrollX();     int sy = getScrollY();     int dx = x - sx;     int dy = y - sy;     if (dx == 0 && dy == 0) {       completeScroll();       setScrollState(SCROLL_STATE_IDLE);       return;     }      setScrollingCacheEnabled(true);     mScrolling = true;     setScrollState(SCROLL_STATE_SETTLING);      final float pageDelta = (float) Math.abs(dx) / (getWidth() + mPageMargin);     int duration = (int) (pageDelta * 100);      velocity = Math.abs(velocity);     if (velocity > 0) {       duration += (duration / (velocity / mBaseLineFlingVelocity)) * mFlingVelocityInfluence;     } else {       duration += 100;     }     duration = Math.min(duration, MAX_SETTLE_DURATION);      mScroller.startScroll(sx, sy, dx, dy, duration);     invalidate();   }    void addNewItem(int position, int index) {     ItemInfo ii = new ItemInfo();     ii.position = position;     ii.object = mAdapter.instantiateItem(this, position);     if (index < 0) {       mItems.add(ii);     } else {       mItems.add(index, ii);     }   }    void dataSetChanged() {     // This method only gets called if our observer is attached, so mAdapter is non-null.      boolean needPopulate = mItems.size() < 3 && mItems.size() < mAdapter.getCount();     int newCurrItem = -1;      for (int i = 0; i < mItems.size(); i++) {       final ItemInfo ii = mItems.get(i);       final int newPos = mAdapter.getItemPosition(ii.object);        if (newPos == PagerAdapter.POSITION_UNCHANGED) {         continue;       }        if (newPos == PagerAdapter.POSITION_NONE) {         mItems.remove(i);         i--;         mAdapter.destroyItem(this, ii.position, ii.object);         needPopulate = true;          if (mCurItem == ii.position) {           // Keep the current item in the valid range           newCurrItem = Math.max(0, Math.min(mCurItem, mAdapter.getCount() - 1));         }         continue;       }        if (ii.position != newPos) {         if (ii.position == mCurItem) {           // Our current item changed position. Follow it.           newCurrItem = newPos;         }          ii.position = newPos;         needPopulate = true;       }     }      Collections.sort(mItems, COMPARATOR);      if (newCurrItem >= 0) {       // TODO This currently causes a jump.       setCurrentItemInternal(newCurrItem, false, true);       needPopulate = true;     }     if (needPopulate) {       populate();       requestLayout();     }   }    void populate() {     if (mAdapter == null) {       return;     }      // Bail now if we are waiting to populate. This is to hold off     // on creating views from the time the user releases their finger to     // fling to a new position until we have finished the scroll to     // that position, avoiding glitches from happening at that point.     if (mPopulatePending) {       if (DEBUG) Log.i(TAG, "populate is pending, skipping for now...");       return;     }      // Also, don't populate until we are attached to a window. This is to     // avoid trying to populate before we have restored our view hierarchy     // state and conflicting with what is restored.     if (getWindowToken() == null) {       return;     }      mAdapter.startUpdate(this);      final int pageLimit = mOffscreenPageLimit;     final int startPos = Math.max(0, mCurItem - pageLimit);     final int N = mAdapter.getCount();     final int endPos = Math.min(N-1, mCurItem + pageLimit);      if (DEBUG) Log.v(TAG, "populating: startPos=" + startPos + " endPos=" + endPos);      // Add and remove pages in the existing list.     int lastPos = -1;     for (int i=0; i<mItems.size(); i++) {       ItemInfo ii = mItems.get(i);       if ((ii.position < startPos || ii.position > endPos) && !ii.scrolling) {         if (DEBUG) Log.i(TAG, "removing: " + ii.position + " @ " + i);         mItems.remove(i);         i--;         mAdapter.destroyItem(this, ii.position, ii.object);       } else if (lastPos < endPos && ii.position > startPos) {         // The next item is outside of our range, but we have a gap         // between it and the last item where we want to have a page         // shown. Fill in the gap.         lastPos++;         if (lastPos < startPos) {           lastPos = startPos;         }         while (lastPos <= endPos && lastPos < ii.position) {           if (DEBUG) Log.i(TAG, "inserting: " + lastPos + " @ " + i);           addNewItem(lastPos, i);           lastPos++;           i++;         }       }       lastPos = ii.position;     }      // Add any new pages we need at the end.     lastPos = mItems.size() > 0 ? mItems.get(mItems.size()-1).position : -1;     if (lastPos < endPos) {       lastPos++;       lastPos = lastPos > startPos ? lastPos : startPos;       while (lastPos <= endPos) {         if (DEBUG) Log.i(TAG, "appending: " + lastPos);         addNewItem(lastPos, -1);         lastPos++;       }     }      if (DEBUG) {       Log.i(TAG, "Current page list:");       for (int i=0; i<mItems.size(); i++) {         Log.i(TAG, "#" + i + ": page " + mItems.get(i).position);       }     }      ItemInfo curItem = null;     for (int i=0; i<mItems.size(); i++) {       if (mItems.get(i).position == mCurItem) {         curItem = mItems.get(i);         break;       }     }     mAdapter.setPrimaryItem(this, mCurItem, curItem != null ? curItem.object : null);      mAdapter.finishUpdate(this);      if (hasFocus()) {       View currentFocused = findFocus();       ItemInfo ii = currentFocused != null ? infoForAnyChild(currentFocused) : null;       if (ii == null || ii.position != mCurItem) {         for (int i=0; i<getChildCount(); i++) {           View child = getChildAt(i);           ii = infoForChild(child);           if (ii != null && ii.position == mCurItem) {             if (child.requestFocus(FOCUS_FORWARD)) {               break;             }           }         }       }     }   }    public static class SavedState extends BaseSavedState {     int position;     Parcelable adapterState;     ClassLoader loader;      public SavedState(Parcelable superState) {       super(superState);     }      @Override     public void writeToParcel(Parcel out, int flags) {       super.writeToParcel(out, flags);       out.writeInt(position);       out.writeParcelable(adapterState, flags);     }      @Override     public String toString() {       return "FragmentPager.SavedState{"           + Integer.toHexString(System.identityHashCode(this))           + " position=" + position + "}";     }      public static final Creator<SavedState> CREATOR         = ParcelableCompat.newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() {           @Override           public SavedState createFromParcel(Parcel in, ClassLoader loader) {             return new SavedState(in, loader);           }           @Override           public SavedState[] newArray(int size) {             return new SavedState[size];           }         });      SavedState(Parcel in, ClassLoader loader) {       super(in);       if (loader == null) {         loader = getClass().getClassLoader();       }       position = in.readInt();       adapterState = in.readParcelable(loader);       this.loader = loader;     }   }    @Override   public Parcelable onSaveInstanceState() {     Parcelable superState = super.onSaveInstanceState();     SavedState ss = new SavedState(superState);     ss.position = mCurItem;     if (mAdapter != null) {       ss.adapterState = mAdapter.saveState();     }     return ss;   }    @Override   public void onRestoreInstanceState(Parcelable state) {     if (!(state instanceof SavedState)) {       super.onRestoreInstanceState(state);       return;     }      SavedState ss = (SavedState)state;     super.onRestoreInstanceState(ss.getSuperState());      if (mAdapter != null) {       mAdapter.restoreState(ss.adapterState, ss.loader);       setCurrentItemInternal(ss.position, false, true);     } else {       mRestoredCurItem = ss.position;       mRestoredAdapterState = ss.adapterState;       mRestoredClassLoader = ss.loader;     }   }    @Override   public void addView(View child, int index, LayoutParams params) {     if (mInLayout) {       addViewInLayout(child, index, params);       child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);     } else {       super.addView(child, index, params);     }      if (USE_CACHE) {       if (child.getVisibility() != GoNE) {         child.setDrawingCacheEnabled(mScrollingCacheEnabled);       } else {         child.setDrawingCacheEnabled(false);       }     }   }    ItemInfo infoForChild(View child) {     for (int i=0; i<mItems.size(); i++) {       ItemInfo ii = mItems.get(i);       if (mAdapter.isViewFromObject(child, ii.object)) {         return ii;       }     }     return null;   }    ItemInfo infoForAnyChild(View child) {     ViewParent parent;     while ((parent=child.getParent()) != this) {       if (parent == null || !(parent instanceof View)) {         return null;       }       child = (View)parent;     }     return infoForChild(child);   }    @Override   protected void onAttachedToWindow() {     super.onAttachedToWindow();     mFirstLayout = true;   }    @Override   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {     // For simple implementation, or internal size is always 0.     // We depend on the container to specify the layout size of     // our view. We can't really know what it is since we will be     // adding and removing different arbitrary views and do not     // want the layout to change as this happens.     setMeasuredDimension(getDefaultSize(0, widthMeasureSpec),         getDefaultSize(0, heightMeasureSpec));      // Children are just made to fill our space.     mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() -         getPaddingLeft() - getPaddingRight(), MeasureSpec.EXACTLY);     mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() -         getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY);      // Make sure we have created all fragments that we need to have shown.     mInLayout = true;     populate();     mInLayout = false;      // Make sure all children have been properly measured.     final int size = getChildCount();     for (int i = 0; i < size; ++i) {       final View child = getChildAt(i);       if (child.getVisibility() != GONE) {         if (DEBUG) Log.v(TAG, "Measuring #" + i + " " + child         + ": " + mChildWidthMeasureSpec);         child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);       }     }   }    @Override   protected void onSizeChanged(int w, int h, int oldw, int oldh) {     super.onSizeChanged(w, h, oldw, oldh);      // Make sure scroll position is set correctly.     if (w != oldw) {       recomputeScrollPosition(w, oldw, mPageMargin, mPageMargin);     }   }    private void recomputeScrollPosition(int width, int oldWidth, int margin, int oldMargin) {     final int widthWithMargin = width + margin;     if (oldWidth > 0) {       final int oldScrollPos = getScrollX();       final int oldwwm = oldWidth + oldMargin;       final int oldScrollItem = oldScrollPos / oldwwm;       final float scrollOffset = (float) (oldScrollPos % oldwwm) / oldwwm;       final int scrollPos = (int) ((oldScrollItem + scrollOffset) * widthWithMargin);       scrollTo(scrollPos, getScrollY());       if (!mScroller.isFinished()) {         // We now return to your regularly scheduled scroll, already in progress.         final int newDuration = mScroller.getDuration() - mScroller.timePassed();         mScroller.startScroll(scrollPos, 0, mCurItem * widthWithMargin, 0, newDuration);       }     } else {       int scrollPos = mCurItem * widthWithMargin;       if (scrollPos != getScrollX()) {         completeScroll();         scrollTo(scrollPos, getScrollY());       }     }   }    @Override   protected void onLayout(boolean changed, int l, int t, int r, int b) {     mInLayout = true;     populate();     mInLayout = false;      final int count = getChildCount();     final int width = r-l;      for (int i = 0; i < count; i++) {       View child = getChildAt(i);       ItemInfo ii;       if (child.getVisibility() != GONE && (ii=infoForChild(child)) != null) {         int loff = (width + mPageMargin) * ii.position;         int childLeft = getPaddingLeft() + loff;         int childTop = getPaddingTop();         if (DEBUG) Log.v(TAG, "Positioning #" + i + " " + child + " f=" + ii.object         + ":" + childLeft + "," + childTop + " " + child.getMeasuredWidth()         + "x" + child.getMeasuredHeight());         child.layout(childLeft, childTop,             childLeft + child.getMeasuredWidth(),             childTop + child.getMeasuredHeight());       }     }     mFirstLayout = false;   }    @Override   public void computeScroll() {     if (DEBUG) Log.i(TAG, "computeScroll: finished=" + mScroller.isFinished());     if (!mScroller.isFinished()) {       if (mScroller.computeScrollOffset()) {         if (DEBUG) Log.i(TAG, "computeScroll: still scrolling");         int oldX = getScrollX();         int oldY = getScrollY();         int x = mScroller.getCurrX();         int y = mScroller.getCurrY();          if (oldX != x || oldY != y) {           scrollTo(x, y);         }          if (mOnPageChangeListener != null) {           final int widthWithMargin = getWidth() + mPageMargin;           final int position = x / widthWithMargin;           final int offsetPixels = x % widthWithMargin;           final float offset = (float) offsetPixels / widthWithMargin;           mOnPageChangeListener.onPageScrolled(position, offset, offsetPixels);         }          // Keep on drawing until the animation has finished.         invalidate();         return;       }     }      // Done with scroll, clean up state.     completeScroll();   }    private void completeScroll() {     boolean needPopulate = mScrolling;     if (needPopulate) {       // Done with scroll, no longer want to cache view drawing.       setScrollingCacheEnabled(false);       mScroller.abortAnimation();       int oldX = getScrollX();       int oldY = getScrollY();       int x = mScroller.getCurrX();       int y = mScroller.getCurrY();       if (oldX != x || oldY != y) {         scrollTo(x, y);       }       setScrollState(SCROLL_STATE_IDLE);     }     mPopulatePending = false;     mScrolling = false;     for (int i=0; i<mItems.size(); i++) {       ItemInfo ii = mItems.get(i);       if (ii.scrolling) {         needPopulate = true;         ii.scrolling = false;       }     }     if (needPopulate) {       populate();     }   }    @Override   public boolean onInterceptTouchEvent(MotionEvent ev) {           final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;      // Always take care of the touch gesture being complete.     if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {       // Release the drag.       if (DEBUG) Log.v(TAG, "Intercept done!");       mIsBeingDragged = false;       mIsUnableToDrag = false;       mActivePointerId = INVALID_POINTER;       return false;     }      // Nothing more to do here if we have decided whether or not we     // are dragging.     if (action != MotionEvent.ACTION_DOWN) {       if (mIsBeingDragged) {         if (DEBUG) Log.v(TAG, "Intercept returning true!");         return true;       }       if (mIsUnableToDrag) {         if (DEBUG) Log.v(TAG, "Intercept returning false!");         return false;       }     }      switch (action) {       case MotionEvent.ACTION_MOVE: {                            final int activePointerId = mActivePointerId;         if (activePointerId == INVALID_POINTER) {           // If we don't have a valid id, the touch down wasn't on content.           break;         }          final int pointerIndex = MotionEventCompat.findPointerIndex(ev, activePointerId);         final float x = MotionEventCompat.getX(ev, pointerIndex);         final float dx = x - mLastMotionX;         final float xDiff = Math.abs(dx);         final float y = MotionEventCompat.getY(ev, pointerIndex);         final float yDiff = Math.abs(y - mLastMotionY);         final int scrollX = getScrollX();         final boolean atEdge = (dx > 0 && scrollX == 0) || (dx < 0 && mAdapter != null &&             scrollX >= (mAdapter.getCount() - 1) * getWidth() - 1);         if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff);          if (canScroll(this, false, (int) dx, (int) x, (int) y)) {           // Nested view has scrollable area under this point. Let it be handled there.           mInitialMotionX = mLastMotionX = x;           mLastMotionY = y;           return false;         }         if (xDiff > mTouchSlop && xDiff > yDiff) {           if (DEBUG) Log.v(TAG, "Starting drag!");           mIsBeingDragged = true;           setScrollState(SCROLL_STATE_DRAGGING);           mLastMotionX = x;           setScrollingCacheEnabled(true);         } else {           if (yDiff > mTouchSlop) {             // The finger has moved enough in the vertical             // direction to be counted as a drag... abort             // any attempt to drag horizontally, to work correctly             // with children that have scrolling containers.             if (DEBUG) Log.v(TAG, "Starting unable to drag!");             mIsUnableToDrag = true;           }         }         break;       }        case MotionEvent.ACTION_DOWN: {                  mLastMotionX = mInitialMotionX = ev.getX();         mLastMotionY = ev.getY();         mActivePointerId = MotionEventCompat.getPointerId(ev, 0);          if (mScrollState == SCROLL_STATE_SETTLING) {           // Let the user 'catch' the pager as it animates.           mIsBeingDragged = true;           mIsUnableToDrag = false;           setScrollState(SCROLL_STATE_DRAGGING);         } else {           completeScroll();           mIsBeingDragged = false;           mIsUnableToDrag = false;         }          if (DEBUG) Log.v(TAG, "Down at " + mLastMotionX + "," + mLastMotionY             + " mIsBeingDragged=" + mIsBeingDragged             + "mIsUnableToDrag=" + mIsUnableToDrag);         break;       }        case MotionEventCompat.ACTION_POINTER_UP:         onSecondaryPointerUp(ev);         break;     }           return mIsBeingDragged;   }    @Override   public boolean onTouchEvent(MotionEvent ev) {     if (mFakeDragging) {       // A fake drag is in progress already, ignore this real one       // but still eat the touch events.       // (It is likely that the user is multi-touching the screen.)       return true;     }      if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {       // Don't handle edge touches immediately -- they may actually belong to one of our       // descendants.       return false;     }      if (mAdapter == null || mAdapter.getCount() == 0) {       // Nothing to present or scroll; nothing to touch.       return false;     }      if (mVelocityTracker == null) {       mVelocityTracker = VelocityTracker.obtain();     }     mVelocityTracker.addMovement(ev);      final int action = ev.getAction();     boolean needsInvalidate = false;      switch (action & MotionEventCompat.ACTION_MASK) {       case MotionEvent.ACTION_DOWN: {                  completeScroll();          // Remember where the motion event started         mLastMotionX = mInitialMotionX = ev.getX();         mActivePointerId = MotionEventCompat.getPointerId(ev, 0);         break;       }       case MotionEvent.ACTION_MOVE:         if (!mIsBeingDragged) {           final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);           final float x = MotionEventCompat.getX(ev, pointerIndex);           final float xDiff = Math.abs(x - mLastMotionX);           final float y = MotionEventCompat.getY(ev, pointerIndex);           final float yDiff = Math.abs(y - mLastMotionY);           if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff);           if (xDiff > mTouchSlop && xDiff > yDiff) {             if (DEBUG) Log.v(TAG, "Starting drag!");             mIsBeingDragged = true;             mLastMotionX = x;             setScrollState(SCROLL_STATE_DRAGGING);             setScrollingCacheEnabled(true);           }         }         if (mIsBeingDragged) {           // Scroll to follow the motion event           final int activePointerIndex = MotionEventCompat.findPointerIndex(               ev, mActivePointerId);           final float x = MotionEventCompat.getX(ev, activePointerIndex);           final float deltaX = mLastMotionX - x;           mLastMotionX = x;           float oldScrollX = getScrollX();           float scrollX = oldScrollX + deltaX;           final int width = getWidth();           final int widthWithMargin = width + mPageMargin;            final int lastItemIndex = mAdapter.getCount() - 1;           final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin);           final float rightBound =               Math.min(mCurItem + 1, lastItemIndex) * widthWithMargin;           if (scrollX < leftBound) {             if (leftBound == 0) {               float over = -scrollX;               needsInvalidate = mLeftEdge.onPull(over / width);             }             scrollX = leftBound;           } else if (scrollX > rightBound) {             if (rightBound == lastItemIndex * widthWithMargin) {               float over = scrollX - rightBound;               needsInvalidate = mRightEdge.onPull(over / width);             }             scrollX = rightBound;           }           // Don't lose the rounded component           mLastMotionX += scrollX - (int) scrollX;           scrollTo((int) scrollX, getScrollY());           if (mOnPageChangeListener != null) {             final int position = (int) scrollX / widthWithMargin;             final int positionOffsetPixels = (int) scrollX % widthWithMargin;             final float positionOffset = (float) positionOffsetPixels / widthWithMargin;             mOnPageChangeListener.onPageScrolled(position, positionOffset,                 positionOffsetPixels);           }         }         break;       case MotionEvent.ACTION_UP:         if (mIsBeingDragged) {           final VelocityTracker velocityTracker = mVelocityTracker;           velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);           int initialVelocity = (int) VelocityTrackerCompat.getXVelocity(               velocityTracker, mActivePointerId);           mPopulatePending = true;           final int widthWithMargin = getWidth() + mPageMargin;           final int scrollX = getScrollX();           final int currentPage = scrollX / widthWithMargin;           int nextPage = initialVelocity > 0 ? currentPage : currentPage + 1;           setCurrentItemInternal(nextPage, true, true, initialVelocity);            mActivePointerId = INVALID_POINTER;           endDrag();           needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease();         }         break;       case MotionEvent.ACTION_CANCEL:         if (mIsBeingDragged) {           setCurrentItemInternal(mCurItem, true, true);           mActivePointerId = INVALID_POINTER;           endDrag();           needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease();         }         break;       case MotionEventCompat.ACTION_POINTER_DOWN: {         final int index = MotionEventCompat.getActionIndex(ev);         final float x = MotionEventCompat.getX(ev, index);         mLastMotionX = x;         mActivePointerId = MotionEventCompat.getPointerId(ev, index);         break;       }       case MotionEventCompat.ACTION_POINTER_UP:         onSecondaryPointerUp(ev);         mLastMotionX = MotionEventCompat.getX(ev,             MotionEventCompat.findPointerIndex(ev, mActivePointerId));         break;     }     if (needsInvalidate) {       invalidate();     }     return true;   }    @Override   public void draw(Canvas canvas) {     super.draw(canvas);     boolean needsInvalidate = false;      final int overScrollMode = ViewCompat.getOverScrollMode(this);     if (overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||         (overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS &&             mAdapter != null && mAdapter.getCount() > 1)) {       if (!mLeftEdge.isFinished()) {         final int restoreCount = canvas.save();         final int height = getHeight() - getPaddingTop() - getPaddingBottom();          canvas.rotate(270);         canvas.translate(-height + getPaddingTop(), 0);         mLeftEdge.setSize(height, getWidth());         needsInvalidate |= mLeftEdge.draw(canvas);         canvas.restoreToCount(restoreCount);       }       if (!mRightEdge.isFinished()) {         final int restoreCount = canvas.save();         final int width = getWidth();         final int height = getHeight() - getPaddingTop() - getPaddingBottom();         final int itemCount = mAdapter != null ? mAdapter.getCount() : 1;          canvas.rotate(90);         canvas.translate(-getPaddingTop(),             -itemCount * (width + mPageMargin) + mPageMargin);         mRightEdge.setSize(height, width);         needsInvalidate |= mRightEdge.draw(canvas);         canvas.restoreToCount(restoreCount);       }     } else {       mLeftEdge.finish();       mRightEdge.finish();     }      if (needsInvalidate) {       // Keep animating       invalidate();     }   }    @Override   protected void onDraw(Canvas canvas) {     super.onDraw(canvas);      // Draw the margin drawable if needed.     if (mPageMargin > 0 && mMarginDrawable != null) {       final int scrollX = getScrollX();       final int width = getWidth();       final int offset = scrollX % (width + mPageMargin);       if (offset != 0) {         // Pages fit completely when settled; we only need to draw when in between         final int left = scrollX - offset + width;         mMarginDrawable.setBounds(left, 0, left + mPageMargin, getHeight());         mMarginDrawable.draw(canvas);       }     }   }       public boolean beginFakeDrag() {     if (mIsBeingDragged) {       return false;     }     mFakeDragging = true;     setScrollState(SCROLL_STATE_DRAGGING);     mInitialMotionX = mLastMotionX = 0;     if (mVelocityTracker == null) {       mVelocityTracker = VelocityTracker.obtain();     } else {       mVelocityTracker.clear();     }     final long time = SystemClock.uptimeMillis();     final MotionEvent ev = MotionEvent.obtain(time, time, MotionEvent.ACTION_DOWN, 0, 0, 0);     mVelocityTracker.addMovement(ev);     ev.recycle();     mFakeDragBeginTime = time;     return true;   }       public void endFakeDrag() {     if (!mFakeDragging) {       throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first.");     }      final VelocityTracker velocityTracker = mVelocityTracker;     velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);     int initialVelocity = (int)VelocityTrackerCompat.getYVelocity(         velocityTracker, mActivePointerId);     mPopulatePending = true;     if ((Math.abs(initialVelocity) > mMinimumVelocity)         || Math.abs(mInitialMotionX-mLastMotionX) >= (getWidth()/3)) {       if (mLastMotionX > mInitialMotionX) {         setCurrentItemInternal(mCurItem-1, true, true);       } else {         setCurrentItemInternal(mCurItem+1, true, true);       }     } else {       setCurrentItemInternal(mCurItem, true, true);     }     endDrag();      mFakeDragging = false;   }       public void fakeDragBy(float xOffset) {     if (!mFakeDragging) {       throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first.");     }      mLastMotionX += xOffset;     float scrollX = getScrollX() - xOffset;     final int width = getWidth();     final int widthWithMargin = width + mPageMargin;      final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin);     final float rightBound =         Math.min(mCurItem + 1, mAdapter.getCount() - 1) * widthWithMargin;     if (scrollX < leftBound) {       scrollX = leftBound;     } else if (scrollX > rightBound) {       scrollX = rightBound;     }     // Don't lose the rounded component     mLastMotionX += scrollX - (int) scrollX;     scrollTo((int) scrollX, getScrollY());     if (mOnPageChangeListener != null) {       final int position = (int) scrollX / widthWithMargin;       final int positionOffsetPixels = (int) scrollX % widthWithMargin;       final float positionOffset = (float) positionOffsetPixels / widthWithMargin;       mOnPageChangeListener.onPageScrolled(position, positionOffset,           positionOffsetPixels);     }      // Synthesize an event for the VelocityTracker.     final long time = SystemClock.uptimeMillis();     final MotionEvent ev = MotionEvent.obtain(mFakeDragBeginTime, time, MotionEvent.ACTION_MOVE,         mLastMotionX, 0, 0);     mVelocityTracker.addMovement(ev);     ev.recycle();   }       public boolean isFakeDragging() {     return mFakeDragging;   }    private void onSecondaryPointerUp(MotionEvent ev) {     final int pointerIndex = MotionEventCompat.getActionIndex(ev);     final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);     if (pointerId == mActivePointerId) {       // This was our active pointer going up. Choose a new       // active pointer and adjust accordingly.       final int newPointerIndex = pointerIndex == 0 ? 1 : 0;       mLastMotionX = MotionEventCompat.getX(ev, newPointerIndex);       mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);       if (mVelocityTracker != null) {         mVelocityTracker.clear();       }     }   }    private void endDrag() {     mIsBeingDragged = false;     mIsUnableToDrag = false;      if (mVelocityTracker != null) {       mVelocityTracker.recycle();       mVelocityTracker = null;     }   }    private void setScrollingCacheEnabled(boolean enabled) {     if (mScrollingCacheEnabled != enabled) {       mScrollingCacheEnabled = enabled;       if (USE_CACHE) {         final int size = getChildCount();         for (int i = 0; i < size; ++i) {           final View child = getChildAt(i);           if (child.getVisibility() != GONE) {             child.setDrawingCacheEnabled(enabled);           }         }       }     }   }       protected boolean canScroll(View v, boolean checkV, int dx, int x, int y) {     if (v instanceof ViewGroup) {       final ViewGroup group = (ViewGroup) v;       final int scrollX = v.getScrollX();       final int scrollY = v.getScrollY();       final int count = group.getChildCount();       // Count backwards - let topmost views consume scroll distance first.       for (int i = count - 1; i >= 0; i--) {         // TODO: Add versioned support here for transfORMed views.         // This will not work for transformed views in Honeycomb+         final View child = group.getChildAt(i);         if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight() &&             y + scrollY >= child.getTop() && y + scrollY < child.getBottom() &&             canScroll(child, true, dx, x + scrollX - child.getLeft(),                 y + scrollY - child.getTop())) {           return true;         }       }     }      return checkV && ViewCompat.canScrollHorizontally(v, -dx);   }    @Override   public boolean dispatchKeyEvent(KeyEvent event) {     // Let the focused view and/or our descendants get the key first     return super.dispatchKeyEvent(event) || executeKeyEvent(event);   }       public boolean executeKeyEvent(KeyEvent event) {     boolean handled = false;     if (event.getAction() == KeyEvent.ACTION_DOWN) {       switch (event.geTKEyCode()) {         case KeyEvent.KEYCODE_DPAD_LEFT:           handled = arrowScroll(FOCUS_LEFT);           break;         case KeyEvent.KEYCODE_DPAD_RIGHT:           handled = arrowScroll(FOCUS_RIGHT);           break;         case KeyEvent.KEYCODE_TAB:           if (KeyEventCompat.hasNoModifiers(event)) {             handled = arrowScroll(FOCUS_FORWARD);           } else if (KeyEventCompat.hasModifiers(event, KeyEvent.META_SHIFT_ON)) {             handled = arrowScroll(FOCUS_BACKWARD);           }           break;       }     }     return handled;   }    public boolean arrowScroll(int direction) {     View currentFocused = findFocus();     if (currentFocused == this) currentFocused = null;      boolean handled = false;      View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused,         direction);     if (nextFocused != null && nextFocused != currentFocused) {       if (direction == View.FOCUS_LEFT) {         // If there is nothing to the left, or this is causing us to         // jump to the right, then what we really want to do is page left.         if (currentFocused != null && nextFocused.getLeft() >= currentFocused.getLeft()) {           handled = pageLeft();         } else {           handled = nextFocused.requestFocus();         }       } else if (direction == View.FOCUS_RIGHT) {         // If there is nothing to the right, or this is causing us to         // jump to the left, then what we really want to do is page right.         if (currentFocused != null && nextFocused.getLeft() <= currentFocused.getLeft()) {           handled = pageRight();         } else {           handled = nextFocused.requestFocus();         }       }     } else if (direction == FOCUS_LEFT || direction == FOCUS_BACKWARD) {       // Trying to move left and nothing there; try to page.       handled = pageLeft();     } else if (direction == FOCUS_RIGHT || direction == FOCUS_FORWARD) {       // Trying to move right and nothing there; try to page.       handled = pageRight();     }     if (handled) {       playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));     }     return handled;   }    boolean pageLeft() {     if (mCurItem > 0) {       setCurrentItem(mCurItem-1, true);       return true;     }     return false;   }    boolean pageRight() {     if (mAdapter != null && mCurItem < (mAdapter.getCount()-1)) {       setCurrentItem(mCurItem+1, true);       return true;     }     return false;   }       @Override   public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {     final int focusableCount = views.size();      final int descendantFocusability = getDescendantFocusability();      if (descendantFocusability != FOCUS_BLOCK_DESCENDANTS) {       for (int i = 0; i < getChildCount(); i++) {         final View child = getChildAt(i);         if (child.getVisibility() == VISIBLE) {           ItemInfo ii = infoForChild(child);           if (ii != null && ii.position == mCurItem) {             child.addFocusables(views, direction, focusableMode);           }         }       }     }      // we add ourselves (if focusable) in all cases except for when we are     // FOCUS_AFTER_DESCENDANTS and there are some descendants focusable. this is     // to avoid the focus search finding layouts when a more precise search     // among the focusable children would be more interesting.     if (       descendantFocusability != FOCUS_AFTER_DESCENDANTS ||         // No focusable descendants         (focusableCount == views.size())) {       // Note that we can't call the superclass here, because it will       // add all views in. So we need to do the same thing View does.       if (!isFocusable()) {         return;       }       if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE &&           isInTouchMode() && !isFocusableInTouchMode()) {         return;       }       if (views != null) {         views.add(this);       }     }   }       @Override   public void addTouchables(ArrayList<View> views) {     // Note that we don't call super.addTouchables(), which means that     // we don't call View.addTouchables(). This is okay because a ViewPager     // is itself not touchable.     for (int i = 0; i < getChildCount(); i++) {       final View child = getChildAt(i);       if (child.getVisibility() == VISIBLE) {         ItemInfo ii = infoForChild(child);         if (ii != null && ii.position == mCurItem) {           child.addTouchables(views);         }       }     }   }       @Override   protected boolean onRequestFocusInDescendants(int direction,       Rect previouslyFocusedRect) {     int index;     int increment;     int end;     int count = getChildCount();     if ((direction & FOCUS_FORWARD) != 0) {       index = 0;       increment = 1;       end = count;     } else {       index = count - 1;       increment = -1;       end = -1;     }     for (int i = index; i != end; i += increment) {       View child = getChildAt(i);       if (child.getVisibility() == VISIBLE) {         ItemInfo ii = infoForChild(child);         if (ii != null && ii.position == mCurItem) {           if (child.requestFocus(direction, previouslyFocusedRect)) {             return true;           }         }       }     }     return false;   }    @Override   public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event) {     // ViewPagers should only report accessibility info for the current page,     // otherwise things get very confusing.      // TODO: Should this note something about the paging container?      final int childCount = getChildCount();     for (int i = 0; i < childCount; i++) {       final View child = getChildAt(i);       if (child.getVisibility() == VISIBLE) {         final ItemInfo ii = infoForChild(child);         if (ii != null && ii.position == mCurItem &&             child.dispatchPopulateAccessibilityEvent(event)) {           return true;         }       }     }      return false;   }    private class PagerObserver extends DataSetObserver {      @Override     public void onChanged() {       dataSetChanged();     }      @Override     public void onInvalidated() {       dataSetChanged();     }   } }