Android:ImageView圖片縮放、居中

幾個重要知識點：

1、布局文件中android:scaleType="matrix" 設置圖片動態縮放

2、matrix.postTranslate(dx,dy); 平移圖片 matrix.postScale(sx,sy,p.x,p.y); 縮放圖片

3、兩點的中點、距離計算方式，限制縮放范圍函數，在指定區域內移動圖片方法

(以下代碼網上很多地方有類似的，僅供參考)

[java]
public class Main extends Activity 
{ 
    private static final int NONE = 0; 
    private static final int DRAG = 1; 
    private static final int ZOOM = 2; 
 
    private int mode = NONE; 
    private float oldDist; 
    private Matrix matrix = new Matrix(); 
    private Matrix savedMatrix = new Matrix(); 
    private PointF start = new PointF(); 
    private PointF mid = new PointF(); 
     
    ImageView view; 
    Bitmap bitmap; 
    DisplayMetrics dm; 
    float minScaleR=0.1f;  //最少縮放比例  
    static final float MAX_SCALE = 4f; //最大縮放比例  
    float dist = 1f; 
 
    @Override 
    public void onCreate(Bundle savedInstanceState) 
    { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
        view = (ImageView) findViewById(R.id.image_view); 
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test); 
         
        dm = new DisplayMetrics(); 
        getWindowManager().getDefaultDisplay().getMetrics(dm); //獲取分辨率  
         
         
        matrix.setScale(minScaleR, minScaleR); //開始先縮小  
        matrix.postTranslate(120, 120);     //圖片的位置相對於imageview的左上角往右往下各偏移120個像素  
        view.setImageMatrix(matrix); 
         
        view.setOnTouchListener(new OnTouchListener() 
        { 
            @Override 
            public boolean onTouch(View v, MotionEvent event) 
            { 
                ImageView view = (ImageView) v; 
                switch (event.getAction() & MotionEvent.ACTION_MASK) 
                { 
                case MotionEvent.ACTION_DOWN:  //單點  
                    Toast.makeText(Main.this, bitmap.getWidth()+"*"+bitmap.getHeight(), Toast.LENGTH_LONG).show(); 
                    savedMatrix.set(matrix); 
                    start.set(event.getX(), event.getY()); 
                    mode = DRAG; 
                    break; 
                case MotionEvent.ACTION_UP:  //單點彈起  
                case MotionEvent.ACTION_POINTER_UP:  //多點彈起  
                    mode = NONE; 
                    break; 
                case MotionEvent.ACTION_POINTER_DOWN:  //多點  
                    oldDist = spacing(event); 
                    if (oldDist > 10f) 
                    { 
                        savedMatrix.set(matrix); 
                        midPoint(mid, event); 
                        mode = ZOOM; 
                    } 
                    break; 
                case MotionEvent.ACTION_MOVE: //按下且在拖動  
                    if (mode == DRAG) 
                    { 
                        matrix.set(savedMatrix); 
                        matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);  //xy方向都可以拖動  
                        //matrix.postTranslate(event.getX() - start.x,0); //只在x軸方向拖動 即左右拖動  上下不動  
                        //matrix.postTranslate(0,event.getY() - start.y);  //只在y軸方向拖動 即上下拖動  左右不動  
                    } 
                    else if (mode == ZOOM) 
                    { 
                        float newDist = spacing(event); 
                        if (newDist > 10f) 
                        { 
                            matrix.set(savedMatrix); 
                            float scale = newDist / oldDist; 
                            matrix.postScale(scale, scale, mid.x, mid.y); 
                        } 
                    } 
                    break; 
                } 
                 
                view.setImageMatrix(matrix); 
                 
                CheckScale();  //限制縮放范圍  
                center();  //居中控制  
                 
                return true; 
            } 
 
             
            //兩點的距離  
            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); 
            } 
             
            //兩點的中點  
            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); 
            } 
        }); 
    } 
     
    //限制最大最小縮放比例    
    protected void CheckScale() 
    { 
        float p[] = new float[9]; 
        matrix.getValues(p); 
        if (mode == ZOOM) 
        { 
            if (p[0] < minScaleR) 
            { 
                matrix.setScale(minScaleR, minScaleR); 
            } 
            if (p[0] > MAX_SCALE) 
            { 
                matrix.set(savedMatrix); 
            } 
        } 
    } 
 
    //自動居中  左右及上下都居中  
    protected void center() 
    { 
        center(true,true); 
    } 
 
    private void center(boolean horizontal, boolean vertical) 
    { 
        Matrix m = new Matrix(); 
        m.set(matrix); 
        RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight()); 
        m.mapRect(rect); 
        float height = rect.height(); 
        float width = rect.width(); 
        float deltaX = 0, deltaY = 0; 
        if (vertical) 
        { 
            //int screenHeight = dm.heightPixels;  //手機屏幕分辨率的高度  
            int screenHeight = 400; 
            if (height < screenHeight) 
            { 
                deltaY = (screenHeight - height)/2 - rect.top; 
            }else if (rect.top > 0) 
            { 
                deltaY = -rect.top; 
            }else if (rect.bottom < screenHeight) 
            { 
                deltaY = view.getHeight() - rect.bottom; 
            } 
        } 
         
        if (horizontal) 
        { 
            //int screenWidth = dm.widthPixels;  //手機屏幕分辨率的寬度  
            int screenWidth = 400; 
            if (width < screenWidth) 
            { 
                deltaX = (screenWidth - width)/2 - rect.left; 
            }else if (rect.left > 0) 
            { 
                deltaX = -rect.left;     
            }else if (rect.right < screenWidth) 
            { 
                deltaX = screenWidth - rect.right; 
            } 
        } 
        matrix.postTranslate(deltaX, deltaY); 
    } 
} 

public class Main extends Activity
{
 private static final int NONE = 0;
 private static final int DRAG = 1;
 private static final int ZOOM = 2;

 private int mode = NONE;
 private float oldDist;
 private Matrix matrix = new Matrix();
 private Matrix savedMatrix = new Matrix();
 private PointF start = new PointF();
 private PointF mid = new PointF();
 
 ImageView view;
 Bitmap bitmap;
 DisplayMetrics dm;
 float minScaleR=0.1f;  //最少縮放比例
 static final float MAX_SCALE = 4f; //最大縮放比例
 float dist = 1f;

 @Override
 public void onCreate(Bundle savedInstanceState)
 {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  view = (ImageView) findViewById(R.id.image_view);
  bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);
  
  dm = new DisplayMetrics();
  getWindowManager().getDefaultDisplay().getMetrics(dm); //獲取分辨率
  
  
  matrix.setScale(minScaleR, minScaleR); //開始先縮小
  matrix.postTranslate(120, 120);  //圖片的位置相對於imageview的左上角往右往下各偏移120個像素
  view.setImageMatrix(matrix);
  
  view.setOnTouchListener(new OnTouchListener()
  {
   @Override
   public boolean onTouch(View v, MotionEvent event)
   {
    ImageView view = (ImageView) v;
    switch (event.getAction() & MotionEvent.ACTION_MASK)
    {
    case MotionEvent.ACTION_DOWN:  //單點
     Toast.makeText(Main.this, bitmap.getWidth()+"*"+bitmap.getHeight(), Toast.LENGTH_LONG).show();
     savedMatrix.set(matrix);
     start.set(event.getX(), event.getY());
     mode = DRAG;
     break;
    case MotionEvent.ACTION_UP:  //單點彈起
    case MotionEvent.ACTION_POINTER_UP:  //多點彈起
     mode = NONE;
     break;
    case MotionEvent.ACTION_POINTER_DOWN:  //多點
     oldDist = spacing(event);
     if (oldDist > 10f)
     {
      savedMatrix.set(matrix);
      midPoint(mid, event);
      mode = ZOOM;
     }
     break;
    case MotionEvent.ACTION_MOVE: //按下且在拖動
     if (mode == DRAG)
     {
      matrix.set(savedMatrix);
      matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);  //xy方向都可以拖動
      //matrix.postTranslate(event.getX() - start.x,0); //只在x軸方向拖動 即左右拖動  上下不動
      //matrix.postTranslate(0,event.getY() - start.y);  //只在y軸方向拖動 即上下拖動  左右不動
     }
     else if (mode == ZOOM)
     {
      float newDist = spacing(event);
      if (newDist > 10f)
      {
       matrix.set(savedMatrix);
       float scale = newDist / oldDist;
       matrix.postScale(scale, scale, mid.x, mid.y);
      }
     }
     break;
    }
    
    view.setImageMatrix(matrix);
    
    CheckScale();  //限制縮放范圍
    center();  //居中控制
    
    return true;
   }

   
   //兩點的距離
   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);
   }
   
   //兩點的中點
   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);
   }
  });
 }
 
 //限制最大最小縮放比例 
 protected void CheckScale()
 {
  float p[] = new float[9];
  matrix.getValues(p);
  if (mode == ZOOM)
  {
   if (p[0] < minScaleR)
   {
    matrix.setScale(minScaleR, minScaleR);
   }
   if (p[0] > MAX_SCALE)
   {
    matrix.set(savedMatrix);
   }
  }
 }

 //自動居中  左右及上下都居中
 protected void center()
 {
  center(true,true);
 }

 private void center(boolean horizontal, boolean vertical)
 {
  Matrix m = new Matrix();
  m.set(matrix);
  RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight());
  m.mapRect(rect);
  float height = rect.height();
  float width = rect.width();
  float deltaX = 0, deltaY = 0;
  if (vertical)
  {
   //int screenHeight = dm.heightPixels;  //手機屏幕分辨率的高度
   int screenHeight = 400;
   if (height < screenHeight)
   {
    deltaY = (screenHeight - height)/2 - rect.top;
   }else if (rect.top > 0)
   {
    deltaY = -rect.top;
   }else if (rect.bottom < screenHeight)
   {
    deltaY = view.getHeight() - rect.bottom;
   }
  }
  
  if (horizontal)
  {
   //int screenWidth = dm.widthPixels;  //手機屏幕分辨率的寬度
   int screenWidth = 400;
   if (width < screenWidth)
   {
    deltaX = (screenWidth - width)/2 - rect.left;
   }else if (rect.left > 0)
   {
    deltaX = -rect.left; 
   }else if (rect.right < screenWidth)
   {
    deltaX = screenWidth - rect.right;
   }
  }
  matrix.postTranslate(deltaX, deltaY);
 }
}[html]
<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    > 
    <ImageView 
        android:layout_width="200dip" 
        android:layout_height="200dip" 
        android:layout_centerHorizontal="true" 
        android:layout_centerVertical="true" 
        android:scaleType="matrix" 
        android:src="@drawable/test" 
        android:id="@+id/image_view"> 
    </ImageView> 
</RelativeLayout> 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <ImageView
        android:layout_width="200dip"
        android:layout_height="200dip"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:scaleType="matrix"
        android:src="@drawable/test"
        android:id="@+id/image_view">
    </ImageView>
</RelativeLayout>