MultiTouch————多点触控，伸缩图片，变换图片位置

前言：当今的手机都支持多点触控功能（可以进行图片伸缩，变换位置），但是我们程序员要怎样结合硬件去实现这个功能呢？

跟随我一起，来学习这个功能

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示例图片：

我是用Genymotion录制的，没有真机上多点触控显示的效果那么好，大家在真机上跑程序，会体会到多点触控功能。（注：Genymotion多点触控快捷键是 ctrl+鼠标指针上下拖动）

具体代码实现：

布局文件 activtiy_main.xml

 1     <?xml version="1.0" encoding="utf-8"?>
 2     <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3         xmlns:tools="http://schemas.android.com/tools"
 4         android:layout_width="match_parent"
 5         android:layout_height="match_parent"
 6         tools:context="com.cnwuth.mutiltouch.MainActivity">
 7
 8         <ImageView
 9             android:id="@+id/iv"
10             android:layout_width="match_parent"
11             android:layout_height="match_parent"
12             android:scaleType="matrix"
13             android:src="@mipmap/ic_launcher"/>
14
15     </RelativeLayout>  

MainActivity.java

  1     package com.cnwuth.mutiltouch;
  2
  3     import android.graphics.Matrix;
  4     import android.graphics.PointF;
  5     import android.support.v7.app.AppCompatActivity;
  6     import android.os.Bundle;
  7     import android.view.MotionEvent;
  8     import android.view.View;
  9     import android.widget.ImageView;
 10
 11     public class MainActivity extends AppCompatActivity implements View.OnTouchListener{
 12
 13         private ImageView mImageView;
 14
 15         //缩放控制
 16         private Matrix mMatrix = new Matrix();
 17         private Matrix savedMatrix = new Matrix();
 18
 19         //不同状态的表示
 20         private static final int NONE = 0;
 21         private static final int DRAG = 1;
 22         private static final int ZOOM = 2;
 23         private int mode = NONE;
 24
 25         //定义第一个按下的点，两只接触点的重点，以及出事的两指按下的距离:
 26         private PointF startPoint = new PointF();
 27         private PointF midPoint = new PointF();
 28         private float oriDis = 1f;
 29
 30         @Override
 31         protected void onCreate(Bundle savedInstanceState) {
 32             super.onCreate(savedInstanceState);
 33             setContentView(R.layout.activity_main);
 34             mImageView = (ImageView) findViewById(R.id.iv);
 35             mImageView.setOnTouchListener(this);
 36         }
 37
 38         @Override
 39         public boolean onTouch(View v, MotionEvent event) {
 40             ImageView view = (ImageView) v;
 41             switch (event.getAction() & MotionEvent.ACTION_MASK)
 42             {
 43                 //单指
 44                 case MotionEvent.ACTION_DOWN:
 45                     mMatrix.set(view.getImageMatrix());
 46                     savedMatrix.set(mMatrix);
 47                     startPoint.set(event.getX(),event.getY());
 48                     mode = DRAG;
 49                     break;
 50                 //双指
 51                 case MotionEvent.ACTION_POINTER_DOWN:
 52                     oriDis = distance(event);
 53                     if (oriDis > 10f)
 54                     {
 55                         savedMatrix.set(mMatrix);
 56                         midPoint = middle(event);
 57                         mode = ZOOM;
 58                     }
 59                     break;
 60                 //手指放开
 61                 case MotionEvent.ACTION_UP:
 62                 case MotionEvent.ACTION_POINTER_UP:
 63                     mode = NONE;
 64                     break;
 65                 //单指滑动事件
 66                 case MotionEvent.ACTION_MOVE:
 67                     if (mode == DRAG)
 68                     {
 69                         //是一个手指拖动
 70                         mMatrix.set(savedMatrix);
 71                         mMatrix.postTranslate(event.getX() - startPoint.x , event.getY() - startPoint.y);
 72                     }
 73                     else if (mode == ZOOM)
 74                     {
 75                         //两个手指滑动
 76                         float newDist = distance(event);
 77                         if (newDist > 10f)
 78                         {
 79                             mMatrix.set(savedMatrix);
 80                             float scale = newDist / oriDis;
 81                             mMatrix.postScale(scale , scale , midPoint.x , midPoint.y);
 82                         }
 83                     }
 84                     break;
 85             }
 86             //设置ImageView的Matrix
 87             view.setImageMatrix(mMatrix);
 88             return true;
 89         }
 90
 91         //计算两个触摸点之间的距离
 92         private float distance(MotionEvent event) {
 93             float x = event.getX(0) - event.getX(1);
 94             float y = event.getY(0) - event.getY(1);
 95             return (float) Math.sqrt(x * x + y * y);
 96         }
 97
 98         //计算两个触摸点的中点
 99         private PointF middle(MotionEvent event){
100             float x = event.getX(0) + event.getX(1);
101             float y = event.getY(0) + event.getY(1);
102             return new PointF(x / 2 , y / 2);
103         }
104     }  

(注：环境需要在Android Studio下运行，并且SDK更新到最新，否则会出现报错)

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