Android 中ViewPager重排序与更新实例详解

Android 中ViewPager重排序与更新实例详解

最近的项目中有栏目订阅功能，在更改栏目顺序以后需要更新ViewPager。类似于网易新闻的频道管理。

在重新排序之后调用了PagerAdapter的notifyDataSetChanged方法，发现ViewPager并没有更新，于是我开始跟踪源码，在调用PagerAdapter的notifyDataSetChanged方法后，会触发Viewpager的dataSetChanged方法。

 void dataSetChanged() {    // This method only gets called if our observer is attached, so mAdapter is non-null.    final int adapterCount = mAdapter.getCount();    mExpectedAdapterCount = adapterCount;    boolean needPopulate = mItems.size() < mOffscreenPageLimit * 2 + 1 &&        mItems.size() < adapterCount;    int newCurrItem = mCurItem;    boolean isUpdating = false;    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--;        if (!isUpdating) {          mAdapter.startUpdate(this);          isUpdating = true;        }        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, adapterCount - 1));          needPopulate = true;        }        continue;      }      if (ii.position != newPos) {        if (ii.position == mCurItem) {          // Our current item changed position. Follow it.          newCurrItem = newPos;        }        ii.position = newPos;        needPopulate = true;      }    }    if (isUpdating) {      mAdapter.finishUpdate(this);    }    Collections.sort(mItems, COMPARATOR);    if (needPopulate) {      // Reset our known page widths; populate will recompute them.      final int childCount = getChildCount();      for (int i = 0; i < childCount; i++) {        final View child = getChildAt(i);        final LayoutParams lp = (LayoutParams) child.getLayoutParams();        if (!lp.isDecor) {          lp.widthFactor = 0.f;        }      }      setCurrentItemInternal(newCurrItem, false, true);      requestLayout();    }  }