Android：在CustomView

Question

我正在尝试实现撤消重做功能，以便在自定义视图中删除图片，并尝试从ANDROID - Undo and Redo in canvas实现解决方案，但是当我点击撤消时，它会填充坐标和圆圈位图下面的同一个绘图对象而不是位图本身，因为撤消应该起作用。请帮助。

public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
         xn=context;
        Log.e(TAG, "The Bitmap is " + bmrot);
        mPaint = new Paint();
        mPaint.setAlpha(0);
        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        mPaint.setAntiAlias(true);
        mPaint.setMaskFilter(new BlurMaskFilter(15, BlurMaskFilter.Blur.SOLID));
        alphaPaint = new Paint();
        alphaPaint.setAlpha(255);
        pcanvas = new Canvas();
        bitmap = bmrot.createBitmap(bmrot.getWidth(), bmrot.getHeight(), Bitmap.Config.ARGB_8888);
        bac=bmrot;
        setBackgroundColor(Color.parseColor("#4d4d4d"));
        Log.e(TAG, "LOGGERHEAD2");
        pcanvas.setBitmap(bitmap);
        pcanvas.drawBitmap(bmrot, reqx, reqy, alphaPaint);

    }