最后我通过参考this和this解决了我的问题
最后 ImageView 类看起来像:
public class RoundedImageView extends ImageView {
private Path mMaskPath;
private Paint mMaskPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
private int mCornerRadius = 10;
public RoundedImageView(Context context) {
super(context);
init();
}
public RoundedImageView(Context context, AttributeSet attributeSet) {
super(context, attributeSet);
init();
}
public RoundedImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
ViewCompat.setLayerType(this, ViewCompat.LAYER_TYPE_SOFTWARE, null);
mMaskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
}
public void setCornerRadius(int cornerRadius) {
mCornerRadius = cornerRadius;
generateMaskPath(getWidth(), getHeight());
invalidate();
}
@Override
protected void onSizeChanged(int w, int h, int oldW, int oldH) {
super.onSizeChanged(w, h, oldW, oldH);
if (w != oldW || h != oldH) {
generateMaskPath(w, h);
}
}
private void generateMaskPath(int w, int h) {
mMaskPath = new Path();
float[] radii = new float[8];
radii[0] = 20; // Goes clockwise, so this is the top left corner start position.
radii[1] = 20; // top left end position.
radii[2] = 20;
radii[3] = 20;
// Skipping 4 and 5 because thats the bottom right corner.
radii[6] = 20;
radii[7] = 20;
mMaskPath.addRoundRect(new RectF(0,0,w,h), radii, Path.Direction.CW);
mMaskPath.setFillType(Path.FillType.INVERSE_WINDING);
}
@SuppressLint("WrongConstant")
@Override
protected void onDraw(Canvas canvas) {
if(canvas.isOpaque()) { // If canvas is opaque, make it transparent
canvas.saveLayerAlpha(0, 0, canvas.getWidth(), canvas.getHeight(), 255, Canvas.HAS_ALPHA_LAYER_SAVE_FLAG);
}
super.onDraw(canvas);
if(mMaskPath != null) {
canvas.drawPath(mMaskPath, mMaskPaint);
}
}
}