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>