Android ImageView绘制圆角效果

前言

Android 开发中，我们经常需要实现图片的圆形/圆角的效果，我们可以使用两种方式来实现这样的效果。一种是使用Xfermode，另一种是BitmapShader来实现。下面我将分别介绍这两种用法。

使用Xfermode的方式实现
使用该方式的关键代码，如下：

  private Bitmap creataBitmap(Bitmap bitmap) {
    //用指定的一个Bitmap来构建一个画布
    Bitmap target = Bitmap.createBitmap(1000,1000, Bitmap.Config.ARGB_8888);
    canvas canvas = new Canvas(target);
    final Paint paint = new Paint();
    paint.setColor(Color.GREEN);
    paint.setAntiAlias(true);
    //在刚才的画布上绘制一个圆形区域
    canvas.drawCircle(500,500,500,paint);
    //设置Xfermode，使用SRC_IN模式,这样可以取到第二张图片重叠后的区域
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    //在画布上绘制第二个需要显示的bitmap
    canvas.drawBitmap(bitmap,0,0,paint);
    return target;
  }

上面代码中看出在指定的画布上绘制了两层图像，一个是半径为500像素的圆形，一个是将目标Bitmap绘制在上面。之间还调用了paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));作用是这两个绘制的效果图叠加后，取得第二个图的交集图。所以，我们先绘制一个圆形，然后绘制Bitmap，交集为圆形，取出的就是圆形区域的Bitmap了。
PorterDuff.Mode中一共有16种效果显示，如下：

可以根据不同的Mode，控制显示的效果图。

开始应用

1.自定义属性在attrs.xml中

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <attr name="borderRadius" fORMat="dimension" />
  <attr name="type">
    <enum name="circle" value="0"/>
    <enum name="round" value="1"/>
  </attr>
  <attr name="src" format="reference"/>
  <declare-styleable name="RoundImageView">
    <attr name="borderRadius"/>
    <attr name="type"/>
    <attr name="src"/>
  </declare-styleable>
</resources>

2.自定义View

public class RoundImageView extends View {
  private int type;
  private static final int TYPE_CIRCLE = 0;
  private static final int TYPE_ROUND = 1;
  //图片
  private Bitmap mSrc;
  //圆角大小
  private int mRadius;
  //高度
  private int mWidth;
  //宽度
  private int mHeight;
  public RoundImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    //获取自定义的属性
    TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.RoundImageView);
    //获取自定以属性的数目
    int count = a.getIndexCount();
    for (int i=0 ; i<count ; i++){
      int attr = a.getIndex(i);
      switch (attr){
        case R.styleable.RoundImageView_borderRadius:
          int defValue = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,10f,getResources().getDisplayMetrics());
          mRadius = a.getDimensionPixelSize(attr, defValue);
          break;
        case R.styleable.RoundImageView_type:
          type = a.getInt(attr,0);
          break;
        case R.styleable.RoundImageView_src:
          mSrc = BitmapFactory.decodeResource(getResources(),a.getResourceId(attr,0));
          break;
      }
    }
    a.recycle();
  }
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    //设置宽度
    int specMode = MeasureSpec.getMode(widthMeasureSpec);
    int specSize = MeasureSpec.getSize(widthMeasureSpec);
    if (specMode == MeasureSpec.EXACTLY){
      mWidth = specSize;
    }else {
      int desireByImg = getPaddingLeft() + getPaddingRight() + mSrc.getWidth();
      if (specMode == MeasureSpec.AT_MOST)// wrap_content
      {
        mWidth = Math.min(desireByImg, specSize);
      } else
        mWidth = desireByImg;
    }
    //设置高度
    specMode = MeasureSpec.getMode(heightMeasureSpec);
    specSize = MeasureSpec.getSize(heightMeasureSpec);
    if (specMode == MeasureSpec.EXACTLY){
      mHeight = specSize;
    }else {
      int desire = getPaddingTop() + getPaddingBottom() + mSrc.getHeight();
      if (specMode == MeasureSpec.AT_MOST)// wrap_content
      {
        mHeight = Math.min(desire, specSize);
      } else
        mHeight = desire;
    }
    setMeasuredDimension(mWidth,mHeight);
  }
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    switch (type){
      case TYPE_CIRCLE:
        int min = Math.min(mWidth,mHeight);
        //从当前存在的Bitmap，按一定的比例创建一个新的Bitmap。
        mSrc = Bitmap.createScaledBitmap(mSrc, min, min, false);
        canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null);
        break;
      case TYPE_ROUND:
        mSrc = Bitmap.createScaledBitmap(mSrc, mWidth, mHeight, false);
        canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null);
        break;
    }
  }
  
  private Bitmap createRoundConerImage(Bitmap source) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    RectF rect = new RectF(0, 0, mWidth, mHeight);
    canvas.drawRoundRect(rect, mRadius, mRadius, paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
  
  private Bitmap createCircleImage(Bitmap source, int min) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(min, min, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    canvas.drawCircle(min/2,min/2,min/2,paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
}

3.布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="Http://schemas.android.com/apk/res/android"
       xmlns:roundview="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools"
       android:id="@+id/activity_main"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:orientation="vertical"
       android:padding="10dp"
       tools:context="mo.yumf.com.myviews.MainActivity">
  <mo.yumf.com.myviews.RoundImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_marginTop="20dp"
    roundview:borderRadius="10dp"
    roundview:src="@drawable/ac_default_icon"
    roundview:type="round"/>
  <mo.yumf.com.myviews.RoundImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_marginTop="20dp"
    roundview:src="@drawable/ac_default_icon"
    roundview:type="circle"/>
</LinearLayout>

上面的自定义View中，存在一个局限，那就是只能在布局中设置要加载的图片资源，不能在代码中设置图片。下面我们使用同样的方式，选择自定义ImageView来实现。

public class RoundImageView extends ImageView {
  private int type;
  private static final int TYPE_CIRCLE = 0;
  private static final int TYPE_ROUND = 1;
  //图片
  private Bitmap mSrc;
  //圆角大小
  private int mRadius;
  public RoundImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    //获取自定义的属性
    TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.RoundImageView);
    //获取自定以属性的数目
    int count = a.getIndexCount();
    for (int i=0 ; i<count ; i++){
      int attr = a.getIndex(i);
      switch (attr){
        case R.styleable.RoundImageView_borderRadius:
          int defValue = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,10f,getResources().getDisplayMetrics());
          mRadius = a.getDimensionPixelSize(attr, defValue);
          break;
        case R.styleable.RoundImageView_type:
          type = a.getInt(attr,0);
          break;
      }
    }
    a.recycle();
  }
  @Override
  protected void onDraw(Canvas canvas) {
    if (getDrawable() != null){
      Bitmap bitmap = getBitmap(getDrawable());
      if (bitmap != null){
        switch (type){
          case TYPE_CIRCLE:
            //获取ImageView中的宽高，取最小值
            int min = Math.min(getMeasuredWidth(),getMeasuredHeight());
            //从当前存在的Bitmap，按一定的比例创建一个新的Bitmap。
            mSrc = Bitmap.createScaledBitmap(bitmap, min, min, false);
            canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null);
            break;
          case TYPE_ROUND:
            mSrc = Bitmap.createScaledBitmap(bitmap, getMeasuredWidth(), getMeasuredHeight(), false);
            canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null);
            break;
        }
      }
    }else {
      super.onDraw(canvas);
    }
  }
  private Bitmap getBitmap(Drawable drawable) {
    if (drawable instanceof BitmapDrawable){
      return ((BitmapDrawable)drawable).getBitmap();
    }else if (drawable instanceof ColorDrawable){
      Rect rect = drawable.getBounds();
      int width = rect.right - rect.left;
      int height = rect.bottom - rect.top;
      int color = ((ColorDrawable)drawable).getColor();
      Bitmap bitmap = Bitmap.createBitmap(width,height, Bitmap.Config.ARGB_8888);
      Canvas canvas = new Canvas(bitmap);
      canvas.drawARGB(Color.alpha(color),Color.red(color), Color.green(color), Color.blue(color));
      return bitmap;
    }else {
      return null;
    }
  }
  
  private Bitmap createRoundConerImage(Bitmap source) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    RectF rect = new RectF(0, 0, getMeasuredWidth(), getMeasuredHeight());
    canvas.drawRoundRect(rect, mRadius, mRadius, paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
  
  private Bitmap createCircleImage(Bitmap source, int min) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(min, min, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    canvas.drawCircle(min/2,min/2,min/2,paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
}

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