Android:ImageView图片缩放、居中

几个重要知识点：

1、布局文件中android:scaleType="matrix" 设置图片动态缩放

2、matrix.postTranslate(dx,dy); 平移图片 matrix.postScale(sx,sy,p.x,p.y); 缩放图片

3、两点的中点、距离计算方式，限制缩放范围函数，在指定区域内移动图片方法

(以下代码网上很多地方有类似的，仅供参考)

 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;  //最少缩放比例
     static final float MAX_SCALE = 4f; //最大缩放比例
     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); //获取分辨率


         matrix.setScale(minScaleR, minScaleR); //开始先缩小
         matrix.postTranslate(120, 120);     //图片的位置相对于imageview的左上角往右往下各偏移120个像素
         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:  //单点
                     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:  //单点弹起
                 case MotionEvent.ACTION_POINTER_UP:  //多点弹起
                     mode = NONE;
                     break;
                 case MotionEvent.ACTION_POINTER_DOWN:  //多点
                     oldDist = spacing(event);
                     if (oldDist > 10f)
                     {
                         savedMatrix.set(matrix);
                         midPoint(mid, event);
                         mode = ZOOM;
                     }
                     break;
                 case MotionEvent.ACTION_MOVE: //按下且在拖动
                     if (mode == DRAG)
                     {
                         matrix.set(savedMatrix);
                         matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);  //xy方向都可以拖动
                         //matrix.postTranslate(event.getX() - start.x,0); //只在x轴方向拖动 即左右拖动  上下不动
                         //matrix.postTranslate(0,event.getY() - start.y);  //只在y轴方向拖动 即上下拖动  左右不动
                     }
                     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();  //限制缩放范围
                 center();  //居中控制

                 return true;
             }


             //两点的距离
             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);
             }

             //两点的中点
             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);
             }
         });
     }

     //限制最大最小缩放比例
     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);
             }
         }
     }

     //自动居中  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;  //手机屏幕分辨率的高度
             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;  //手机屏幕分辨率的宽度
             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);
     }
 }

 <?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>