Android 单指触控拖拽，两指触控缩放

 import android.app.Activity;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.Window;
 import android.widget.FrameLayout;
 import android.widget.FrameLayout.LayoutParams;

 public class MainActivity extends Activity {

     View view;
     public static final int DRAG = 1;
     public static final int SCALE = 2;
     int mode = 1;
     float lengthOld = 1;//初始化两指之间原长

     //初始化圆点高宽,java代码中操作的宽高都是像素值，dp*density转成px
     int width = 40;
     int height = 40;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
         setContentView(R.layout.activity_main);
         Log.e("TAG", "像素密度："+getResources().getDisplayMetrics().density);
         view = findViewById(R.id.view);
     }

     /**
      * 在MainActivity中画一个圆
      * Activity重写onTouchEvent，触摸监听
      * getRawX(),getRawY()是获取手机屏幕上的点到屏幕左上角顶点的距离
      * getX(),getY()是获取视图坐标，子视图在父视图中的位置
      */
     @Override
     public boolean onTouchEvent(MotionEvent event) {
         //记录坐标，圆点距离视图顶点
         int x = (int) event.getX();
         int y = (int) event.getY();

         //多指触控
         //获取事件源，并通过event.getActionMasked()加入多点触控支持
         switch (event.getAction() & event.getActionMasked()) {
         case MotionEvent.ACTION_DOWN:
             //单指移动
             mode = DRAG;
             break;
         case MotionEvent.ACTION_POINTER_DOWN:
             //多指缩放
             Log.e("TAG", "多指移动");
             mode = SCALE;
             //计算两指间开始的原长
             lengthOld = calculation(event);
             break;
         case MotionEvent.ACTION_UP:
             lengthOld = 1;//复位
             break;
         case MotionEvent.ACTION_MOVE:
             if(mode == DRAG){
                 //单指，直接设置坐标
                 FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(width, height);
                 params.setMargins(x, y, 0, 0);
                 view.setLayoutParams(params);

             }else{
                 //两指缩放，要计算缩放比例
                 float scale = calculation(event) / lengthOld;
                 width = (int) (view.getWidth() * scale);
                 height = (int) (view.getHeight() * scale);

                 FrameLayout.LayoutParams params = (LayoutParams) view.getLayoutParams();
                 params.width = width;
                 params.height = height;
                 view.setLayoutParams(params);
             }
             break;
         }

         return true;
     }

     private float calculation(MotionEvent event) {

         float x1 = event.getX();
         float x2 = event.getX(1);
         float y1 = event.getY();
         float y2 = event.getY(1);

         return (float) Math.sqrt(Math.pow((x1-x2), 2)+Math.pow((y1-y2), 2));
     }
 }

xml中设置

 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent" >

     <View
         android:id="@+id/view"
         android:layout_width="20dp"
         android:layout_height="20dp"
         android:background="@drawable/oval" />

 </FrameLayout>