android - PorterDuff mask 留下不透明的黑色背景

我正在尝试使用定义为九个补丁的遮罩遮罩FrameLayout。但是，尽管它在旧版本（例如4.4.4）的5.0+上可以正常工作，但该修补程序会留下不透明的黑色背景。除了在渲染到屏幕或还原到软件层之前绘制到屏幕外的位图之外，还有什么方法可以避免这种情况？

public class MaskedLayout extends FrameLayout {

    private final static PorterDuffXfermode DST_IN = new PorterDuffXfermode(PorterDuff.Mode.DST_IN);
    private final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private NinePatchDrawable mMask;

    private boolean mShowTail = true;
    private boolean mReverseLayout;

    public ChatBubbleLayout(Context context) {
        this(context, null);
    }

    public ChatBubbleLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ChatBubbleLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setWillNotDraw(false);
        setLayerType(LAYER_TYPE_HARDWARE, mPaint);

        mMask = createMask(R.drawable.mask);
    }

    private NinePatchDrawable createMask(@DrawableRes int res) {
        final Bitmap maskBitmap = BitmapFactory.decodeResource(getResources(), res);
        final NinePatch patch = new NinePatch(maskBitmap, maskBitmap.getNinePatchChunk(), "Mask");
        return new NinePatchDrawable(getResources(), patch);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        if (w != oldw || h != oldh) {
            mMask.setBounds(0, 0, w, h);
        }
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        mMask.getPaint().setXfermode(DST_IN);
        mMask.draw(canvas);
    }
}

最佳答案

尝试这个：

public class MaskedLayout extends FrameLayout {

    private NinePatchDrawable mMask;

    public MaskedLayout(Context context) {
        this(context, null);
    }

    public MaskedLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MaskedLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mMask = (NinePatchDrawable) getResources().getDrawable(R.drawable.mask);
        mMask.getPaint().setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mMask.setBounds(0, 0, w, h);
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        canvas.saveLayer(null, null, Canvas.ALL_SAVE_FLAG);
        super.dispatchDraw(canvas);
        mMask.draw(canvas);
        canvas.restore();
    }
}