Android ImageView随手势变化动态缩放图片

<span style="font-size:18px;">import android.annotation.SuppressLint; 
import android.content.Context; 
import android.graphics.Matrix; 
import android.graphics.PointF; 
import android.util.AttributeSet; 
import android.util.FloatMath; 
import android.util.Log; 
import android.view.MotionEvent; 
import android.widget.ImageView; 
 
@SuppressLint("FloatMath") 
public class ScaleImageView extends ImageView { 
 
  private Matrix matrix=new Matrix(); 
  private Matrix savedMatrix=new Matrix(); 
   
  static final int NONE = 0;  
  static final int DRAG = 1;  
  static final int ZOOM = 2;  
  int mode = NONE;  
 
  // Remember some things for zooming  
  PointF start = new PointF();  
  PointF mid = new PointF();  
  float oldDist = 1f;  
   
  public ScaleImageView(Context context) { 
    super(context); 
  } 
 
  public ScaleImageView(Context context, AttributeSet attrs, int defStyle) { 
    super(context, attrs, defStyle); 
  } 
 
  public ScaleImageView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
  } 
   
  private float spacing(MotionEvent event) {  
    float x = event.getX(0) - event.getX(1);  
    float y = event.getY(0) - event.getY(1);  
    return FloatMath.sqrt(x * x + y * y);  
   }  
 
  
   private void midPoint(PointF point, MotionEvent event) {  
    float x = event.getX(0) + event.getX(1);  
    float y = event.getY(0) + event.getY(1);  
    point.set(x / 2, y / 2);  
   }  
 
  @Override 
  public boolean onTouchEvent(MotionEvent event) { 
    if(event.getActionMasked()==MotionEvent.ACTION_POINTER_UP) 
      Log.d("Infor", "多点操作"); 
    switch(event.getActionMasked()){ 
    case MotionEvent.ACTION_DOWN: 
       matrix.set(getImageMatrix()); 
       savedMatrix.set(matrix); 
       start.set(event.getX(),event.getY()); 
       Log.d("Infor", "触摸了..."); 
       mode=DRAG; 
       break; 
    case MotionEvent.ACTION_POINTER_DOWN: //多点触控 
       oldDist=this.spacing(event); 
      if(oldDist>10f){ 
       Log.d("Infor", "oldDist"+oldDist); 
       savedMatrix.set(matrix); 
       midPoint(mid,event); 
       mode=ZOOM; 
      } 
      break; 
    case MotionEvent.ACTION_POINTER_UP: 
      mode=NONE; 
      break; 
    case MotionEvent.ACTION_MOVE: 
      if(mode==DRAG){     //此实现图片的拖动功能... 
        matrix.set(savedMatrix); 
        matrix.postTranslate(event.getX()-start.x, event.getY()-start.y); 
      } 
      else if(mode==ZOOM){// 此实现图片的缩放功能... 
       float newDist=spacing(event); 
       if(newDist>10){ 
         matrix.set(savedMatrix); 
         float scale=newDist/oldDist; 
         matrix.postScale(scale, scale, mid.x, mid.y);         
       } 
        } 
      break; 
    } 
    setImageMatrix(matrix); 
    return true; 
  } 
}</span>