图片的拖动与释放
原理图：
1)
2)
代码如下：
1、在drawable目录下导入要演示的图片
2、main.xml
package com.njupt.drag_scale1;import android.app.Activity;import android.graphics.Matrix;import android.graphics.PointF;import android.os.Bundle;import android.util.FloatMath;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.widget.ImageView;public class MainActivity extends Activity { /** Called when the activity is first created. */private ImageView iv; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); iv = (ImageView) findViewById(R.id.iv); iv.setOnTouchListener(new MyOnTouchListener()); } private final class MyOnTouchListener implements OnTouchListener{ private PointF startPoint = new PointF();//初始点 private Matrix mCurrentMatrix = new Matrix();//图片初始的matrix值 private Matrix mMatrix = new Matrix();//来一个临时的matrix private PointF midPointF;//中心点 private float midDistance;//两点间的距离 private int type = 0; private final static int DRAG = 1; private final static int SCALE = 2; public boolean onTouch(View v, MotionEvent event) {// TODO Auto-generated method stubint action = event.getAction()&MotionEvent.ACTION_MASK;switch (action) {case MotionEvent.ACTION_DOWN://手指按下float x = event.getX();float y = event.getY();startPoint.set(x, y);mCurrentMatrix.set(iv.getImageMatrix());//图片没有移动的位置type = DRAG;break;case MotionEvent.ACTION_POINTER_1_DOWN://屏幕上有一根手指，再按下一根手指mCurrentMatrix.set(iv.getImageMatrix());//图片没有缩放的大小midPointF = getMidPointF(event);midDistance = getMidDistance(event);type = SCALE;break;case MotionEvent.ACTION_MOVE://手指移动if(type == DRAG){mMatrix.set(mCurrentMatrix);float dx = event.getX() - startPoint.x;float dy = event.getY() - startPoint.y;mMatrix.postTranslate(dx, dy);}else if(type == SCALE){mMatrix.set(mCurrentMatrix);float distance = getMidDistance(event);//得到当前两个手指间的距离float sx = distance/midDistance;//得到缩放的倍数mMatrix.postScale(sx, sx, midPointF.x, midPointF.y);}break;case MotionEvent.ACTION_UP://手指弹起case MotionEvent.ACTION_POINTER_1_UP://弹起一根手指，屏幕上还有一根手指type = 0;break;default:break;}iv.setImageMatrix(mMatrix);return true;} } //得到中心点private PointF getMidPointF(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);}//计算两点间的距离private float getMidDistance(MotionEvent event){float dx = event.getX(1) - event.getX(0);float dy = event.getY(1) - event.getY(0);return FloatMath.sqrt(dx*dx + dy*dy);}}