Android通过多点触控的方式对图片进行缩放的实例代码

public class ZoomImageView extends View { 
 /** 
  * 初始化状态常量 
  */ 
 public static final int STATUS_INIT = 1; 
 /** 
  * 图片放大状态常量 
  */ 
 public static final int STATUS_ZOOM_OUT = 2; 
 /** 
  * 图片缩小状态常量 
  */ 
 public static final int STATUS_ZOOM_IN = 3; 
 /** 
  * 图片拖动状态常量 
  */ 
 public static final int STATUS_MOVE = 4; 
 /** 
  * 用于对图片进行移动和缩放变换的矩阵 
  */ 
 private Matrix matrix = new Matrix(); 
 /** 
  * 待展示的Bitmap对象 
  */ 
 private Bitmap sourceBitmap; 
 /** 
  * 记录当前操作的状态，可选值为STATUS_INIT、STATUS_ZOOM_OUT、STATUS_ZOOM_IN和STATUS_MOVE 
  */ 
 private int currentStatus; 
 /** 
  * ZoomImageView控件的宽度 
  */ 
 private int width; 
 /** 
  * ZoomImageView控件的高度 
  */ 
 private int height; 
 /** 
  * 记录两指同时放在屏幕上时，中心点的横坐标值 
  */ 
 private float centerPointX; 
 /** 
  * 记录两指同时放在屏幕上时，中心点的纵坐标值 
  */ 
 private float centerPointY; 
 /** 
  * 记录当前图片的宽度，图片被缩放时，这个值会一起变动 
  */ 
 private float currentBitmapWidth; 
 /** 
  * 记录当前图片的高度，图片被缩放时，这个值会一起变动 
  */ 
 private float currentBitmapHeight; 
 /** 
  * 记录上次手指移动时的横坐标 
  */ 
 private float lastXMove = -1; 
 /** 
  * 记录上次手指移动时的纵坐标 
  */ 
 private float lastYMove = -1; 
 /** 
  * 记录手指在横坐标方向上的移动距离 
  */ 
 private float movedDistanceX; 
 /** 
  * 记录手指在纵坐标方向上的移动距离 
  */ 
 private float movedDistanceY; 
 /** 
  * 记录图片在矩阵上的横向偏移值 
  */ 
 private float totalTranslateX; 
 /** 
  * 记录图片在矩阵上的纵向偏移值 
  */ 
 private float totalTranslateY; 
 /** 
  * 记录图片在矩阵上的总缩放比例 
  */ 
 private float totalRatio; 
 /** 
  * 记录手指移动的距离所造成的缩放比例 
  */ 
 private float scaledRatio; 
 /** 
  * 记录图片初始化时的缩放比例 
  */ 
 private float initRatio; 
 /** 
  * 记录上次两指之间的距离 
  */ 
 private double lastFingerDis; 
 /** 
  * ZoomImageView构造函数，将当前操作状态设为STATUS_INIT。 
  * 
  * @param context 
  * @param attrs 
  */ 
 public ZoomImageView(Context context, AttributeSet attrs) { 
  super(context, attrs); 
  currentStatus = STATUS_INIT; 
 } 
 /** 
  * 将待展示的图片设置进来。 
  * 
  * @param bitmap 
  *   待展示的Bitmap对象 
  */ 
 public void setImageBitmap(Bitmap bitmap) { 
  sourceBitmap = bitmap; 
  invalidate(); 
 } 
 @Override 
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) { 
  super.onLayout(changed, left, top, right, bottom); 
  if (changed) { 
   // 分别获取到ZoomImageView的宽度和高度 
   width = getWidth(); 
   height = getHeight(); 
  } 
 } 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
  switch (event.getActionMasked()) { 
  case MotionEvent.ACTION_POINTER_DOWN: 
   if (event.getPointerCount() == 2) { 
    // 当有两个手指按在屏幕上时，计算两指之间的距离 
    lastFingerDis = distanceBetweenFingers(event); 
   } 
   break; 
  case MotionEvent.ACTION_MOVE: 
   if (event.getPointerCount() == 1) { 
    // 只有单指按在屏幕上移动时，为拖动状态 
    float xMove = event.getX(); 
    float yMove = event.getY(); 
    if (lastXMove == -1 && lastYMove == -1) { 
     lastXMove = xMove; 
     lastYMove = yMove; 
    } 
    currentStatus = STATUS_MOVE; 
    movedDistanceX = xMove - lastXMove; 
    movedDistanceY = yMove - lastYMove; 
    // 进行边界检查，不允许将图片拖出边界 
    if (totalTranslateX + movedDistanceX > 0) { 
     movedDistanceX = 0; 
    } else if (width - (totalTranslateX + movedDistanceX) > currentBitmapWidth) { 
     movedDistanceX = 0; 
    } 
    if (totalTranslateY + movedDistanceY > 0) { 
     movedDistanceY = 0; 
    } else if (height - (totalTranslateY + movedDistanceY) > currentBitmapHeight) { 
     movedDistanceY = 0; 
    } 
    // 调用onDraw()方法绘制图片 
    invalidate(); 
    lastXMove = xMove; 
    lastYMove = yMove; 
   } else if (event.getPointerCount() == 2) { 
    // 有两个手指按在屏幕上移动时，为缩放状态 
    centerPointBetweenFingers(event); 
    double fingerDis = distanceBetweenFingers(event); 
    if (fingerDis > lastFingerDis) { 
     currentStatus = STATUS_ZOOM_OUT; 
    } else { 
     currentStatus = STATUS_ZOOM_IN; 
    } 
    // 进行缩放倍数检查，最大只允许将图片放大4倍，最小可以缩小到初始化比例 
    if ((currentStatus == STATUS_ZOOM_OUT && totalRatio < 4 * initRatio) 
      || (currentStatus == STATUS_ZOOM_IN && totalRatio > initRatio)) { 
     scaledRatio = (float) (fingerDis / lastFingerDis); 
     totalRatio = totalRatio * scaledRatio; 
     if (totalRatio > 4 * initRatio) { 
      totalRatio = 4 * initRatio; 
     } else if (totalRatio < initRatio) { 
      totalRatio = initRatio; 
     } 
     // 调用onDraw()方法绘制图片 
     invalidate(); 
     lastFingerDis = fingerDis; 
    } 
   } 
   break; 
  case MotionEvent.ACTION_POINTER_UP: 
   if (event.getPointerCount() == 2) { 
    // 手指离开屏幕时将临时值还原 
    lastXMove = -1; 
    lastYMove = -1; 
   } 
   break; 
  case MotionEvent.ACTION_UP: 
   // 手指离开屏幕时将临时值还原 
   lastXMove = -1; 
   lastYMove = -1; 
   break; 
  default: 
   break; 
  } 
  return true; 
 } 
 /** 
  * 根据currentStatus的值来决定对图片进行什么样的绘制操作。 
  */ 
 @Override 
 protected void onDraw(Canvas canvas) { 
  super.onDraw(canvas); 
  switch (currentStatus) { 
  case STATUS_ZOOM_OUT: 
  case STATUS_ZOOM_IN: 
   zoom(canvas); 
   break; 
  case STATUS_MOVE: 
   move(canvas); 
   break; 
  case STATUS_INIT: 
   initBitmap(canvas); 
  default: 
   canvas.drawBitmap(sourceBitmap, matrix, null); 
   break; 
  } 
 } 
 /** 
  * 对图片进行缩放处理。 
  * 
  * @param canvas 
  */ 
 private void zoom(Canvas canvas) { 
  matrix.reset(); 
  // 将图片按总缩放比例进行缩放 
  matrix.postScale(totalRatio, totalRatio); 
  float scaledWidth = sourceBitmap.getWidth() * totalRatio; 
  float scaledHeight = sourceBitmap.getHeight() * totalRatio; 
  float translateX = 0f; 
  float translateY = 0f; 
  // 如果当前图片宽度小于屏幕宽度，则按屏幕中心的横坐标进行水平缩放。否则按两指的中心点的横坐标进行水平缩放 
  if (currentBitmapWidth < width) { 
   translateX = (width - scaledWidth) / 2f; 
  } else { 
   translateX = totalTranslateX * scaledRatio + centerPointX * (1 - scaledRatio); 
   // 进行边界检查，保证图片缩放后在水平方向上不会偏移出屏幕 
   if (translateX > 0) { 
    translateX = 0; 
   } else if (width - translateX > scaledWidth) { 
    translateX = width - scaledWidth; 
   } 
  } 
  // 如果当前图片高度小于屏幕高度，则按屏幕中心的纵坐标进行垂直缩放。否则按两指的中心点的纵坐标进行垂直缩放 
  if (currentBitmapHeight < height) { 
   translateY = (height - scaledHeight) / 2f; 
  } else { 
   translateY = totalTranslateY * scaledRatio + centerPointY * (1 - scaledRatio); 
   // 进行边界检查，保证图片缩放后在垂直方向上不会偏移出屏幕 
   if (translateY > 0) { 
    translateY = 0; 
   } else if (height - translateY > scaledHeight) { 
    translateY = height - scaledHeight; 
   } 
  } 
  // 缩放后对图片进行偏移，以保证缩放后中心点位置不变 
  matrix.postTranslate(translateX, translateY); 
  totalTranslateX = translateX; 
  totalTranslateY = translateY; 
  currentBitmapWidth = scaledWidth; 
  currentBitmapHeight = scaledHeight; 
  canvas.drawBitmap(sourceBitmap, matrix, null); 
 } 
 /** 
  * 对图片进行平移处理 
  * 
  * @param canvas 
  */ 
 private void move(Canvas canvas) { 
  matrix.reset(); 
  // 根据手指移动的距离计算出总偏移值 
  float translateX = totalTranslateX + movedDistanceX; 
  float translateY = totalTranslateY + movedDistanceY; 
  // 先按照已有的缩放比例对图片进行缩放 
  matrix.postScale(totalRatio, totalRatio); 
  // 再根据移动距离进行偏移 
  matrix.postTranslate(translateX, translateY); 
  totalTranslateX = translateX; 
  totalTranslateY = translateY; 
  canvas.drawBitmap(sourceBitmap, matrix, null); 
 } 
 /** 
  * 对图片进行初始化操作，包括让图片居中，以及当图片大于屏幕宽高时对图片进行压缩。 
  * 
  * @param canvas 
  */ 
 private void initBitmap(Canvas canvas) { 
  if (sourceBitmap != null) { 
   matrix.reset(); 
   int bitmapWidth = sourceBitmap.getWidth(); 
   int bitmapHeight = sourceBitmap.getHeight(); 
   if (bitmapWidth > width || bitmapHeight > height) { 
    if (bitmapWidth - width > bitmapHeight - height) { 
     // 当图片宽度大于屏幕宽度时，将图片等比例压缩，使它可以完全显示出来 
     float ratio = width / (bitmapWidth * 1.0f); 
     matrix.postScale(ratio, ratio); 
     float translateY = (height - (bitmapHeight * ratio)) / 2f; 
     // 在纵坐标方向上进行偏移，以保证图片居中显示 
     matrix.postTranslate(0, translateY); 
     totalTranslateY = translateY; 
     totalRatio = initRatio = ratio; 
    } else { 
     // 当图片高度大于屏幕高度时，将图片等比例压缩，使它可以完全显示出来 
     float ratio = height / (bitmapHeight * 1.0f); 
     matrix.postScale(ratio, ratio); 
     float translateX = (width - (bitmapWidth * ratio)) / 2f; 
     // 在横坐标方向上进行偏移，以保证图片居中显示 
     matrix.postTranslate(translateX, 0); 
     totalTranslateX = translateX; 
     totalRatio = initRatio = ratio; 
    } 
    currentBitmapWidth = bitmapWidth * initRatio; 
    currentBitmapHeight = bitmapHeight * initRatio; 
   } else { 
    // 当图片的宽高都小于屏幕宽高时，直接让图片居中显示 
    float translateX = (width - sourceBitmap.getWidth()) / 2f; 
    float translateY = (height - sourceBitmap.getHeight()) / 2f; 
    matrix.postTranslate(translateX, translateY); 
    totalTranslateX = translateX; 
    totalTranslateY = translateY; 
    totalRatio = initRatio = 1f; 
    currentBitmapWidth = bitmapWidth; 
    currentBitmapHeight = bitmapHeight; 
   } 
   canvas.drawBitmap(sourceBitmap, matrix, null); 
  } 
 } 
 /** 
  * 计算两个手指之间的距离。 
  * 
  * @param event 
  * @return 两个手指之间的距离 
  */ 
 private double distanceBetweenFingers(MotionEvent event) { 
  float disX = Math.abs(event.getX(0) - event.getX(1)); 
  float disY = Math.abs(event.getY(0) - event.getY(1)); 
  return Math.sqrt(disX * disX + disY * disY); 
 } 
 /** 
  * 计算两个手指之间中心点的坐标。 
  * 
  * @param event 
  */ 
 private void centerPointBetweenFingers(MotionEvent event) { 
  float xPoint0 = event.getX(0); 
  float yPoint0 = event.getY(0); 
  float xPoint1 = event.getX(1); 
  float yPoint1 = event.getY(1); 
  centerPointX = (xPoint0 + xPoint1) / 2; 
  centerPointY = (yPoint0 + yPoint1) / 2; 
 } 
} 

<?xml version="1.0" encoding="utf-8"?> 
<com.example.photowallfallsdemo.ZoomImageView xmlns:android="http://schemas.android.com/apk/res/android" 
 android:id="@+id/zoom_image_view" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
 android:background="#000000" > 
</com.example.photowallfallsdemo.ZoomImageView> 

public class ImageDetailsActivity extends Activity { 
 private ZoomImageView zoomImageView; 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  requestWindowFeature(Window.FEATURE_NO_TITLE); 
  setContentView(R.layout.image_details); 
  zoomImageView = (ZoomImageView) findViewById(R.id.zoom_image_view); 
  String imagePath = getIntent().getStringExtra("image_path"); 
  Bitmap bitmap = BitmapFactory.decodeFile(imagePath); 
  zoomImageView.setImageBitmap(bitmap); 
 } 
} 

private void addImage(Bitmap bitmap, int imageWidth, int imageHeight) { 
 LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(imageWidth, 
   imageHeight); 
 if (mImageView != null) { 
  mImageView.setImageBitmap(bitmap); 
 } else { 
  ImageView imageView = new ImageView(getContext()); 
  imageView.setLayoutParams(params); 
  imageView.setImageBitmap(bitmap); 
  imageView.setScaleType(ScaleType.FIT_XY); 
  imageView.setPadding(5, 5, 5, 5); 
  imageView.setTag(R.string.image_url, mImageUrl); 
  imageView.setOnClickListener(new OnClickListener() { 
   @Override 
   public void onClick(View v) { 
    Intent intent = new Intent(getContext(), ImageDetailsActivity.class); 
    intent.putExtra("image_path", getImagePath(mImageUrl)); 
    getContext().startActivity(intent); 
   } 
  }); 
  findColumnToAdd(imageView, imageHeight).addView(imageView); 
  imageViewList.add(imageView); 
 } 
}

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
 package="com.example.photowallfallsdemo" 
 android:versionCode="1" 
 android:versionName="1.0" > 
 <uses-sdk 
  android:minSdkVersion="14" 
  android:targetSdkVersion="17" /> 
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
 <uses-permission android:name="android.permission.INTERNET" /> 
 <application 
  android:allowBackup="true" 
  android:icon="@drawable/ic_launcher" 
  android:label="@string/app_name" 
  android:theme="@style/AppTheme" > 
  <activity 
   android:name="com.example.photowallfallsdemo.MainActivity" 
   android:label="@string/app_name" > 
   <intent-filter> 
    <action android:name="android.intent.action.MAIN" /> 
    <category android:name="android.intent.category.LAUNCHER" /> 
   </intent-filter> 
  </activity> 
  <activity android:name="com.example.photowallfallsdemo.ImageDetailsActivity" > 
  </activity> 
 </application> 
</manifest>