如何在android中撤消/重做画布上绘制的形状

public class MyDrawingView extends View {
    private List<Shape> shapes; // 保存绘制的形状
    private Stack<Shape> undoStack; // 撤销栈
    private Stack<Shape> redoStack; // 重做栈

    public MyDrawingView(Context context) {
        super(context);
        shapes = new ArrayList<>();
        undoStack = new Stack<>();
        redoStack = new Stack<>();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        for (Shape shape : shapes) {
            shape.draw(canvas);
        }
    }

    public void addShape(Shape shape) {
        shapes.add(shape);
        undoStack.push(shape);
        redoStack.clear(); // 新增绘制操作后清空重做栈
        invalidate(); // 重新绘制
    }

    public void undo() {
        if (!undoStack.isEmpty()) {
            Shape shape = undoStack.pop();
            redoStack.push(shape);
            invalidate(); // 重新绘制
        }
    }

    public void redo() {
        if (!redoStack.isEmpty()) {
            Shape shape = redoStack.pop();
            undoStack.push(shape);
            invalidate(); // 重新绘制
        }
    }
}

public abstract class Shape {
    public abstract void draw(Canvas canvas);
}

// 示例：绘制一个矩形形状
public class RectangleShape extends Shape {
    private int left, top, right, bottom;

    public RectangleShape(int left, int top, int right, int bottom) {
        this.left = left;
        this.top = top;
        this.right = right;
        this.bottom = bottom;
    }

    @Override
    public void draw(Canvas canvas) {
        Paint paint = new Paint();
        paint.setColor(Color.RED);
        canvas.drawRect(left, top, right, bottom, paint);
    }
}