图片的拖拽和缩放

package com.example.dragandscalephotodemo;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.MotionEvent;

import uk.co.senab.photoview.PhotoView;

public class MainActivity extends AppCompatActivity {

private PhotoView photoView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    photoView = (PhotoView) findViewById(R.id.photo_view);
}

/**
 * 事件分发的方法 ,需要activty把事件传给photoview ,photoview才能接受到我们的触摸事件
 */
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {

    //activity接受到事件分发之后,我们手动处理触摸事件,只给传给我们自己的onTouchEvent方法;
    onTouchEvent(ev);
    return true;
}

//手指按下的坐标
float downX;
float downY;

//手指移动前的坐标
float lastX;
float lastY;
boolean moveble = false;
boolean isMorePoint = false;

@Override
public boolean onTouchEvent(MotionEvent event) {
    super.onTouchEvent(event);

    //接受多指触控需要用 event.getAction() & MotionEvent.ACTION_MASK 来获得当前的触摸事件
    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            downX = event.getX();
            downY = event.getY();
            lastX = downX;
            lastY = downY;

            if (downX > photoView.getX()
                    && downX < photoView.getX() + photoView.getWidth()
                    && downY > photoView.getY()
                    && downY < photoView.getY() + photoView.getHeight()
                    ) {
                moveble = true;
            } else {
                moveble = false;
            }
            break;
        case MotionEvent.ACTION_MOVE:

            //当前手指摸出的坐标
            float currentX = event.getX();
            float currentY = event.getY();

            //我手指移动的距离
            float gapX = currentX - lastX;
            float gapY = currentY - lastY;

            //  如果点击位置不在图片上的话不做任何逻辑处理  moveble ==true 的时候做处理
            if (moveble) {
                if (isMorePoint) {
                    //多指的时候 把事件交给photoview去处理 ,它自己会根据事件去做放大缩小的逻辑 ,
                    photoView.dispatchTouchEvent(event);
                } else {
                    //单指的时候  拖拽的逻辑  设置图片新的位置    ==    原来的位置 + 手指移动的距离
                    photoView.setX(photoView.getX() + gapX);
                    photoView.setY(photoView.getY() + gapY);
                }
            }
            lastX = event.getX();
            lastY = event.getY();
            break;
        case MotionEvent.ACTION_UP:

            break;

        //除了第一个手指之外别的手指按下时触发
        case MotionEvent.ACTION_POINTER_DOWN:
            isMorePoint = true;
            break;
        //除了第一个手指之外别的手指抬起时触发
        case MotionEvent.ACTION_POINTER_UP:
            isMorePoint = false;
            break;
    }

    return true;
}

}