如何在Android中一起执行放大/缩小,旋转

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

public class MyImageView extends View {
    private Matrix matrix;
    private float scale = 1f;
    private float rotation = 0f;
    private PointF midPoint;
    private GestureDetector gestureDetector;
    private ScaleGestureDetector scaleGestureDetector;

    public MyImageView(Context context) {
        super(context);
        init();
    }

    public MyImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        matrix = new Matrix();
        midPoint = new PointF();
        gestureDetector = new GestureDetector(getContext(), new MyGestureListener());
        scaleGestureDetector = new ScaleGestureDetector(getContext(), new MyScaleGestureListener());
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        gestureDetector.onTouchEvent(event);
        scaleGestureDetector.onTouchEvent(event);
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.save();
        canvas.translate(getWidth() / 2, getHeight() / 2);
        canvas.scale(scale, scale, midPoint.x, midPoint.y);
        canvas.rotate(rotation, midPoint.x, midPoint.y);
        // 绘制图片
        // ...
        canvas.restore();
    }

    private class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
            // 计算旋转角度
            rotation -= distanceX / getWidth() * 360;
            invalidate();
            return true;
        }
    }

    private class MyScaleGestureListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            // 计算缩放中点
            midPoint.set(detector.getFocusX(), detector.getFocusY());
            return true;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            // 计算缩放比例
            scale *= detector.getScaleFactor();
            invalidate();
            return true;
        }
    }
}