Android利用Xfermode剪裁圆角

public class HotCityView extends LinearLayout {
    private LinearLayout ll_item_container1, ll_item_container2;
    private int itemH, itemSpace;
    private int padding;
    private Paint clipPaint;
    private RectF clipRect;
    private Bitmap maskBitmap;
    private int cornerSize;

    public HotCityView(@NonNull Context context) {
        this(context, null);
    }

    public HotCityView(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public HotCityView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        setOrientation(VERTICAL);

        inflate(context, R.layout.m_layout_hot_city, this);

        padding = (int) getResources().getDimension(R.dimen.list_lr_margin1);
        setPadding(padding, 0, padding, 0);

        itemH = PixelUtil.dp2px(109);
        itemSpace = (int) getResources().getDimension(R.dimen.hot_item_space);
        cornerSize = PixelUtil.dp2px(8);

        ll_item_container1 = findViewById(R.id.m_hot_city_item_container1);
        ll_item_container2 = findViewById(R.id.m_hot_city_item_container2);

        clipPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        clipPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        if (clipRect == null || getMeasuredWidth() == 0) {
            clipRect = new RectF(padding, 0, getMeasuredWidth() - padding, getMeasuredHeight());

            maskBitmap = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_4444);
            Canvas c = new Canvas(maskBitmap);
            //在蒙版上画需要覆盖的图形
            c.drawRoundRect(clipRect, cornerSize, cornerSize, clipPaint);
        }

        //保存还没有绘制之前的图层
        int layerId = canvas.saveLayer(clipRect, clipPaint, Canvas.ALL_SAVE_FLAG);
        //绘制底部图层
        super.dispatchDraw(canvas);

        //设置混合模式，实现view的四个圆角
        clipPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        canvas.drawBitmap(maskBitmap, 0, 0, clipPaint);
        clipPaint.setXfermode(null);
        //恢复之前的图层，要不然背景是黑色的
        canvas.restoreToCount(layerId);
    }


    //这种方式也可以实现裁剪效果，但是需要5.0以上
    private void clipRoundView() {
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
            ViewOutlineProvider viewOutlineProvider = new ViewOutlineProvider() {
                @Override
                public void getOutline(View view, Outline outline) {
                    //修改outline为特定形状
                    outline.setRoundRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), cornerSize);
                }
            };
            //重新设置形状
            setOutlineProvider(viewOutlineProvider);
            //添加背景或者是ImageView的时候失效，添加如下设置
            setClipToOutline(true);
        }
    }
}