Canvas;如何追溯删除形状

Question

所以我在自定义 View class 中使用 onDraw 在 RelativeLayout + TableLayout 上绘制形状一切正常，我还有另一个 class 用来画从 A 点到 B 点等的线。示例如下：

我的目标：

如果我将手指从 A 点（objectA）拖动到 B 点（objectB），如何从 canvas 中删除这 2 个视图对象？我添加了一个方法：

objectA.delete();
objectB.delete();

当我拖动手指通过 MotionEvent 时应该删除 A 和 B，但它只删除一个而没有删除另一个，所以我认为它不具有追溯力？

以下代码：

switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
   /// get the child that corresponds to the first touch
    DotView objectA = getChildForTouch((TableLayout) v, x, y);

    return true;
 case MotionEvent.ACTION_MOVE:

 ///used the x - y to get the object for every other  shape the user`S finger passes over.
 DotView objectB = getChildForTouch((TableLayout) v, x, y);


   /// just update positions
   line.setCoords(mStartX, mStartY, (int) x, (int) y);

 objectA.delete(); ///Delete first shape
 objectB.delete(); ///Delete second shape

break;

case MotionEvent.ACTION_UP:
    ///Gets the last shape where the user released their fingers
    endView = getChildForTouch((TableLayout) v, x, y);
break;

里面的删除方法：DotView extends View class:

private static class DotView extends View {

        private static final int DEFAULT_SIZE = 100;
        private Paint mPaint = new Paint();
        private Rect mBorderRect = new Rect();
        private Paint mCirclePaint = new Paint();
        private int mRadius = DEFAULT_SIZE / 4;

        public DotView(Context context) {
            super(context);
            mPaint.setStrokeWidth(2.0f);
            mPaint.setStyle(Style.STROKE);
            mPaint.setColor(Color.RED);
            mCirclePaint.setColor(Color.CYAN);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.parseColor("#0099cc"));
            mBorderRect.left = 0;
            mBorderRect.top = 0;
            mBorderRect.right = getMeasuredWidth();
            mBorderRect.bottom = getMeasuredHeight();
            canvas.drawRect(mBorderRect, mPaint);
            canvas.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2,
                    mRadius, mCirclePaint);
        }


        public void delete(){
        mPaint.setColor(Color.TRANSPARENT);
        }

    }

只是一些简单的假删除圈子

提前谢谢大家..如果需要可以提供更多代码。

编辑： 如果我能以任何其他方式完成此任务，请随时分享。（在网格上画圆圈并删除我用手指画线的圆圈）

Answer 1

首先尝试将您的 delete() 方法更改为：

public void delete(){
    mPaint.setColor(Color.TRANSPARENT);
    invalidate();
}

您需要让您的 View 知道您希望它自己重绘（这就是 invalidate() 调用的原因）。

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