Android多点触摸交互处理，放大缩小图片

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"
    android:id="@+id/frame">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/img"
        android:background="@drawable/paoku00199"/>

</FrameLayout>

private  float currentDistance=0;
    private float lastDistance=-1;
    private FrameLayout frame;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        frame= (FrameLayout) findViewById(R.id.frame);
        final ImageView img= (ImageView) findViewById(R.id.img);

        frame.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()){
                    case MotionEvent.ACTION_DOWN: //触摸按下
                        Log.i("MotionEvent","ACTION_DOWN");
                        break;
                }
                switch (event.getAction()){
                    case MotionEvent.ACTION_MOVE: //触摸移动
                        Log.i("MotionEvent","ACTION_MOVE");

                        FrameLayout.LayoutParams layoutParams = (FrameLayout.LayoutParams) img.getLayoutParams();

                        if(event.getPointerCount()==1) {
                            //单个触摸点，并拖动图片
                            System.out.println(String.format("X:%f,Y:%f", event.getX(), event.getY()));

                            layoutParams.leftMargin = (int) event.getX()-10;
                            layoutParams.topMargin = (int) event.getY()-10;

                            img.setLayoutParams(layoutParams);
                        }

                        System.out.println("pointer count 触摸点个数"+event.getPointerCount());//触摸点个数
                        //多个触摸点的坐标


                        //手势放大缩小图片
                        if (event.getPointerCount()>=2){
                            System.out.println(String.format("多个触摸点的坐标X1:%f;Y1:%f", event.getX(0), event.getX(0)));
                            float offsetX=event.getX(0)-event.getX(1);
                            float offsetY=event.getY(0)-event.getY(1);
                            currentDistance=(float)Math.sqrt(offsetX*offsetX+offsetY*offsetY);

                            if(lastDistance<0){
                                lastDistance=currentDistance;
                            }else {
                               if(currentDistance-lastDistance>5){    //5px;有误差
                                   FrameLayout.LayoutParams lp = (FrameLayout.LayoutParams) img.getLayoutParams();
                                   System.out.println("放大");
                                   lp.width= (int) (1.1f*img.getWidth());
                                   lp.height=(int) (1.1f*img.getHeight());
                                   img.setLayoutParams(lp);
                                   lastDistance=currentDistance;  //放大
                               }else if (lastDistance-currentDistance>5){
                                   lastDistance=currentDistance;    //缩小
                                   FrameLayout.LayoutParams lp = (FrameLayout.LayoutParams) img.getLayoutParams();
                                   lp.width= (int) (0.9f*img.getWidth());
                                   lp.height=(int) (0.9f*img.getHeight());
                                   img.setLayoutParams(lp);
                               }

                            }
                        }
                        break;
                }
                switch (event.getAction()){
                    case MotionEvent.ACTION_UP: //触摸弹起
                        Log.i("MotionEvent","ACTION_UP");
                        break;
                }

                return true;//true:需要催发后续事件；false：不需要须发后续事件(只能执行一次)
            }
        });
    }

private  float currentDistance=0;
    private float lastDistance=-1;