Android编程实现自定义ImageView圆图功能的方法

public static class RoundedDrawable extends Drawable {
    protected final float cornerRadius;
    protected final int margin;
    protected final RectF mRect = new RectF(),
        mBitmapRect;
    protected final BitmapShader bitmapShader;
    protected final Paint paint;
    public RoundedDrawable(Bitmap bitmap, int cornerRadius, int margin) {
      this.cornerRadius = cornerRadius;
      this.margin = margin;
      bitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
      mBitmapRect = new RectF (margin, margin, bitmap.getWidth() - margin, bitmap.getHeight() - margin);
      paint = new Paint();
      paint.setAntiAlias(true);
      paint.setShader(bitmapShader);
    }
    @Override
    protected void onBoundsChange(Rect bounds) {
      super.onBoundsChange(bounds);
      mRect.set(margin, margin, bounds.width() - margin, bounds.height() - margin);
      // Resize the original bitmap to fit the new bound
      Matrix shaderMatrix = new Matrix();
      shaderMatrix.setRectToRect(mBitmapRect, mRect, Matrix.ScaleToFit.FILL);
      bitmapShader.setLocalMatrix(shaderMatrix);
    }
    @Override
    public void draw(Canvas canvas) {
      canvas.drawRoundRect(mRect, cornerRadius, cornerRadius, paint);
    }
    @Override
    public int getOpacity() {
      return PixelFormat.TRANSLUCENT;
    }
    @Override
    public void setAlpha(int alpha) {
      paint.setAlpha(alpha);
    }
    @Override
    public void setColorFilter(ColorFilter cf) {
      paint.setColorFilter(cf);
    }
  }

public class URoundedImageView extends ImageView {
  private Paint mBitmapPaint,mBackgroundPaint;
  private BitmapShader mBitmapShader;
  private RectF mBitmapRect , mRect;
  private int borderWidth;
  private Bitmap mBitmap;
  private Matrix shaderMatrix;
  public URoundedImageView(Context context, AttributeSet attrs,
      int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
  }
  public URoundedImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }
  public URoundedImageView(Context context) {
    super(context);
    init();
  }
  private void init(){
    mBitmapPaint = new Paint();
    mBitmapPaint.setAntiAlias(true);
    mBackgroundPaint = new Paint();
    mBackgroundPaint.setAntiAlias(true);
    mBackgroundPaint.setColor(Color.WHITE);
    borderWidth = 5;
    mRect = new RectF();
    shaderMatrix = new Matrix();
  }
  @Override
  protected void onLayout(boolean changed, int left, int top, int right,
      int bottom) {
    // TODO Auto-generated method stub
    super.onLayout(changed, left, top, right, bottom);
  }
  @Override
  protected void onDraw(Canvas canvas) {
    mBitmap = ((BitmapDrawable) getDrawable()).getBitmap();
    if (getWidth() == 0 || getHeight() == 0 || mBitmap == null) {
      return;
    }
    int w = getWidth();
    int h = getHeight();
    int radius = Math.min(w, h) / 2;
    canvas.drawCircle(w / 2, h / 2, radius, mBackgroundPaint);
    //传入bitmap初始化位图着色器
    if (mBitmapShader == null) {
      mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP,
          Shader.TileMode.CLAMP);
    }
    if (mBitmapRect == null) {
      mBitmapRect = new RectF(borderWidth, borderWidth,
          mBitmap.getWidth() - borderWidth, mBitmap.getHeight()
              - borderWidth);
    }
    mBitmapPaint.setShader(mBitmapShader);
    mRect.set(borderWidth, borderWidth, w - borderWidth, h - borderWidth);
    //对bitmap原始图进行缩放
    shaderMatrix.setRectToRect(mBitmapRect, mRect, Matrix.ScaleToFit.FILL);
    mBitmapShader.setLocalMatrix(shaderMatrix);
    canvas.drawRoundRect(mRect, radius, radius, mBitmapPaint);
  }
}