android 图片点击一下就放大到全屏,再点一下就回到原界面

/*android 图片点击一下就放大到全屏,再点一下就回到原界面 */  
public class MainActivity extends Activity {  
  
       
    /** Called when the activity is first created. */    
    Bitmap bp=null;    
    ImageView imageview;    
    float scaleWidth;    
    float scaleHeight;    
        
    int h;    
    boolean num=false;    
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
  
  DisplayMetrics dm=new DisplayMetrics();//创建矩阵    
  getWindowManager().getDefaultDisplay().getMetrics(dm);  
    
    imageview=(ImageView)findViewById(R.id.imageview);    
    bp=BitmapFactory.decodeResource(getResources(),R.drawable.xiaoyua);    
    int width=bp.getWidth();    
    int height=bp.getHeight();    
    int w=dm.widthPixels; //得到屏幕的宽度   
    int h=dm.heightPixels; //得到屏幕的高度  
    scaleWidth=((float)w)/width;    
    scaleHeight=((float)h)/height;    
    imageview.setImageBitmap(bp);    
}    
    @Override    
    public boolean onTouchEvent(MotionEvent event) {    
                
           switch(event.getAction()){    
                
           case MotionEvent.ACTION_DOWN:  //当屏幕检测到第一个触点按下之后就会触发到这个事件。  
            if(num==true)        {    
                    Matrix matrix= new Matrix();    
                    matrix.postScale(scaleWidth,scaleHeight);    
                        
					Bitmap newBitmap=Bitmap.createBitmap(bp, 0, 0, bp.getWidth(), bp.getHeight(),
						matrix, true);    
                    imageview.setImageBitmap(newBitmap);    
                    num=false;    
                    }    
            else{    
                    Matrix matrix = new Matrix();    
                    matrix.postScale(1.0f,1.0f);    
                    Bitmap newBitmap=Bitmap.createBitmap(bp, 0, 0, bp.getWidth(), bp.getHeight(),
						matrix, true);    
					imageview.setImageBitmap(newBitmap);    
					num=true;    
            }    
                    break;    
            }    
                             
           return super.onTouchEvent(event);    
    }         
}  

布局文件的xml: