android 如何利用手势放大和缩小一个图片？



   

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import android.app.Activity; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.Matrix; 
import android.graphics.PointF; 
import android.hardware.SensorManager; 
import android.os.Bundle; 
import android.util.FloatMath; 
import android.util.Log; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.View.OnTouchListener; 
import android.widget.Button; 
import android.widget.ImageView; 

public class Touch extends Activity implements OnTouchListener, OnClickListener { 
   private static final String TAG = "Touch" ; 

   // These matrices will be used to move and zoom image 
   Matrix matrix = new Matrix(); 
   Matrix savedMatrix = new Matrix(); 
   PointF start = new PointF(); 
   PointF mid = new PointF(); 
   float  oldDist; 
   private ImageView view; 
   private Button zoomIn, zoomOut; 
   //button zoom 
   private float scaleWidth = 1; 
   private float scaleHeight = 1; 
   private Bitmap bmp, zoomedBMP; 
   private int zoom_level = 0; 
   private static final double ZOOM_IN_SCALE = 1.25;//放大系数 
   private static final double ZOOM_OUT_SCALE = 0.8;//缩小系数 
   // We can be in one of these 3 states 
   static final int NONE = 0; 
   static final int DRAG = 1; 
   static final int ZOOM = 2; 
   int mode = NONE; 

   @Override 
   public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.main); 
      //放大按钮 
      zoomIn = (Button) findViewById(R.id.zoom_in); 
       //缩小按钮 
      zoomOut = (Button) findViewById(R.id.zoom_out); 
      zoomIn.setOnClickListener(this); 
      zoomOut.setOnClickListener(this); 
      view = (ImageView) findViewById(R.id.imageView); 
      view.setOnTouchListener(this); 
      //取得drawable中图片，放大，缩小，多点触摸的作用对象 
       bmp = BitmapFactory.decodeResource(Touch.this.getResources(), R.drawable.butterfly); 

              } 

   public boolean onTouch(View v, MotionEvent event) { 
// Handle touch events here... 
ImageView view = (ImageView) v; 

// Handle touch events here... 
switch (event.getAction() & MotionEvent.ACTION_MASK) { 
//设置拖拉模式 
case MotionEvent.ACTION_DOWN: 
savedMatrix.set(matrix); 
start.set(event.getX(), event.getY()); 
Log.d(TAG, "mode=DRAG" ); 
mode = DRAG; 
break; 

case MotionEvent.ACTION_UP: 
case MotionEvent.ACTION_POINTER_UP: 
mode = NONE; 
Log.d(TAG, "mode=NONE" ); 
break; 
//设置多点触摸模式 
case MotionEvent.ACTION_POINTER_DOWN: 
oldDist = spacing(event); 
Log.d(TAG, "oldDist=" + oldDist); 
if (oldDist > 10f) { 
savedMatrix.set(matrix); 
midPoint(mid, event); 
mode = ZOOM; 
Log.d(TAG, "mode=ZOOM" ); 
} 
break; 
//若为DRAG模式，则点击移动图片 
case MotionEvent.ACTION_MOVE: 
if (mode == DRAG) { 
matrix.set(savedMatrix); 
// 设置位移 
matrix.postTranslate(event.getX() - start.x, 
event.getX() - start.x); 
} 
//若为ZOOM模式，则多点触摸缩放 
else if (mode == ZOOM) { 
float newDist = spacing(event); 
Log.d(TAG, "newDist=" + newDist); 
if (newDist > 10f) { 
matrix.set(savedMatrix); 
float scale = newDist / oldDist; 
//设置缩放比例和图片中点位置 
matrix.postScale(scale, scale, mid.x, mid.y); 
} 
} 
break; 
} 

// Perform the transformation 
view.setImageMatrix(matrix); 

return true; // indicate event was handled 
   } 
//计算移动距离 
   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); 
   } 
//计算中点位置 
   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); 
   } 

//放大，缩小按钮点击事件 
@Override 
public void onClick(View v) { 
        if(v == zoomIn){ 
                enlarge(); 
        }else if (v == zoomOut) { 
                small(); 
        } 
} 

//按钮点击缩小函数 
private void small() { 
int bmpWidth = bmp.getWidth(); 
int bmpHeight = bmp.getHeight(); 

scaleWidth = (float) (scaleWidth * ZOOM_OUT_SCALE); 
scaleHeight = (float) (scaleHeight * ZOOM_OUT_SCALE); 

Matrix matrix = new Matrix(); 
matrix.postScale(scaleWidth, scaleHeight); 
zoomedBMP = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight, matrix, 
true); 
view.setImageBitmap(zoomedBMP); 
} 

//按钮点击放大函数 
private void enlarge() { 
        try { 
                int bmpWidth = bmp.getWidth(); 
                int bmpHeight = bmp.getHeight(); 

                scaleWidth = (float) (scaleWidth * ZOOM_IN_SCALE); 
                scaleHeight = (float) (scaleHeight * ZOOM_IN_SCALE); 

                Matrix matrix = new Matrix(); 
                matrix.postScale(scaleWidth, scaleHeight); 
                zoomedBMP = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight, matrix, 
                                true); 
                view.setImageBitmap(zoomedBMP); 
        } catch (Exception e) { 
                //can't zoom because of memory issue, just ignore, no big deal 
        } 
} 
}