Android多点触控缩放拖拽实例

下面通过一个例子来学习实现图片的拖拉功能：

程序运行示意图：1.初始化界面  2.为缩小的界面  3.为放大的界面

主界面的activity_layout.xml的布局代码如下：

<RelativeLayout 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"
    >

    <ImageView 
        android:id="@+id/show_img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:scaleType="matrix"
        android:src="@drawable/s001"
        android:background="#ff0000"
        android:contentDescription="@string/app_name"/>

</RelativeLayout>

我们把一张图片（大小超过手机屏幕）的图片放在drawable-mdpi文件中。

图片资源如下：

MainActivity.java的代码如下：

package com.shen.draganddrop;

import android.app.Activity;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class MainActivity extends Activity {

	private ImageView  imageView;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		imageView = (ImageView) findViewById(R.id.show_img);
		imageView.setOnTouchListener(new ImageTouchListener());
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
	
	private class ImageTouchListener implements OnTouchListener
	{
		
		//声明一个坐标点
		private PointF startPoint;
		//声明并实例化一个Matrix来控制图片
		private Matrix matrix = new Matrix();
		//声明并实例化当前图片的Matrix
		private Matrix mCurrentMatrix = new Matrix();
		
		
		//缩放时初始的距离
		private float startDistance;
		//拖拉的标记
		private static final int DRAG = 1;
		//缩放的标记
		private static final int ZOOM = 2;
		//标识记录
		private int mode;
		//缩放的中间点
		private PointF midPoint;
		
		@Override
		public boolean onTouch(View v, MotionEvent event) {
			switch (event.getAction()&MotionEvent.ACTION_MASK) {
			case MotionEvent.ACTION_DOWN:
				System.out.println("ACTION_DOWN");
				Log.w("Drag", "ACTION_DOWN");
				//此时处于拖拉方式下
				mode = DRAG;
				//获得当前按下点的坐标
				startPoint = new PointF(event.getX(),event.getY());
				//把当前图片的Matrix设置为按下图片的Matrix
				mCurrentMatrix.set(imageView.getImageMatrix());
				break;
			case MotionEvent.ACTION_MOVE:
				Log.w("Drag", "ACTION_MOVE");
				//根据不同的模式执行相应的缩放或者拖拉操作
				switch (mode) {
				case DRAG:
					//移动的x坐标的距离
					float dx = event.getX() - startPoint.x;
					//移动的y坐标的距离
					float dy = event.getY() - startPoint.y;
					//设置Matrix当前的matrix
					matrix.set(mCurrentMatrix);
					//告诉matrix要移动的x轴和Y轴的距离
					matrix.postTranslate(dx, dy);
					break;
				case ZOOM:
					//计算缩放的距离
					float endDistance = distance(event);
					//计算缩放比率
					float scale = endDistance / startDistance;
					//设置当前的Matrix
					matrix.set(mCurrentMatrix);
					//设置缩放的参数
					matrix.postScale(scale, scale, midPoint.x, midPoint.y);
					break;
				default:
					break;
				}
				
				break;
			//已经有一个手指按住屏幕，再有一个手指按下屏幕就会触发该事件
			case MotionEvent.ACTION_POINTER_DOWN:
				Log.w("Drag", "ACTION_POINTER_DOWN");
				//此时为缩放模式
				mode = ZOOM;
				//计算开始时两个点的距离
				startDistance = distance(event);
				//当两个点的距离大于10时才进行缩放操作
				if(startDistance > 10)
				{
					//计算中间点
					midPoint = mid(event);
					//得到进行缩放操作之前，照片的绽放倍数
					mCurrentMatrix.set(imageView.getImageMatrix());
				}
				break;
			//已经有一个手指离开屏幕，还有手指在屏幕上时就会触发该事件
			case MotionEvent.ACTION_POINTER_UP:
				Log.w("Drag", "ACTION_POINTER_UP");
				mode = 0;
				break;
			case MotionEvent.ACTION_UP:
				Log.w("Drag", "ACTION_UP");
				mode = 0;
				break;
			default:
				break;
			}
			//按照Matrix的要求移动图片到某一个位置
			imageView.setImageMatrix(matrix);
			//返回true表明我们会消费该动作，不需要父控件进行进一步的处理
			return true;
		}
		
		
	}
	
	public static float distance(MotionEvent event)
	{
		float dx = event.getX(1) - event.getX(0);
		float dy = event.getY(1) - event.getY(0);
		
		return (float) Math.sqrt(dx*dx + dy*dy);
	}
	
	public static PointF mid(MotionEvent event)
	{
		float x = (event.getX(1) - event.getX(0)) /2;
		float y = (event.getY(1) - event.getY(0)) /2;
		return new PointF(x,y);
	}
}

程序源码下载

http://download.csdn.net/detail/cqtddt/8308631