Android编程实现图片的浏览、缩放、拖动和自动居中效果

/**
 * 图片浏览、缩放、拖动、自动居中
 */
public class Touch extends Activity implements OnTouchListener {
 Matrix matrix = new Matrix();
 Matrix savedMatrix = new Matrix();
 DisplayMetrics dm;
 ImageView imgView;
 Bitmap bitmap;
 float minScaleR;// 最小缩放比例
 static final float MAX_SCALE = 4f;// 最大缩放比例
 static final int NONE = 0;// 初始状态
 static final int DRAG = 1;// 拖动
 static final int ZOOM = 2;// 缩放
 int mode = NONE;
 PointF prev = new PointF();
 PointF mid = new PointF();
 float dist = 1f;
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.scale);
  imgView = (ImageView) findViewById(R.id.imag);// 获取控件
  bitmap = BitmapFactory.decodeResource(getResources(), this.getIntent()
    .getExtras().getInt("IMG"));// 获取图片资源
  imgView.setImageBitmap(bitmap);// 填充控件
  imgView.setOnTouchListener(this);// 设置触屏监听
  dm = new DisplayMetrics();
  getWindowManager().getDefaultDisplay().getMetrics(dm);// 获取分辨率
  minZoom();
  center();
  imgView.setImageMatrix(matrix);
 }
 /**
  * 触屏监听
  */
 public boolean onTouch(View v, MotionEvent event) {
  switch (event.getAction() & MotionEvent.ACTION_MASK) {
  // 主点按下
  case MotionEvent.ACTION_DOWN:
   savedMatrix.set(matrix);
   prev.set(event.getX(), event.getY());
   mode = DRAG;
   break;
  // 副点按下
  case MotionEvent.ACTION_POINTER_DOWN:
   dist = spacing(event);
   // 如果连续两点距离大于10，则判定为多点模式
   if (spacing(event) > 10f) {
    savedMatrix.set(matrix);
    midPoint(mid, event);
    mode = ZOOM;
   }
   break;
  case MotionEvent.ACTION_UP:
  case MotionEvent.ACTION_POINTER_UP:
   mode = NONE;
   break;
  case MotionEvent.ACTION_MOVE:
   if (mode == DRAG) {
    matrix.set(savedMatrix);
    matrix.postTranslate(event.getX() - prev.x, event.getY()
      - prev.y);
   } else if (mode == ZOOM) {
    float newDist = spacing(event);
    if (newDist > 10f) {
     matrix.set(savedMatrix);
     float tScale = newDist / dist;
     matrix.postScale(tScale, tScale, mid.x, mid.y);
    }
   }
   break;
  }
  imgView.setImageMatrix(matrix);
  CheckView();
  return true;
 }
 /**
  * 限制最大最小缩放比例，自动居中
  */
 private void CheckView() {
  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);
   }
  }
  center();
 }
 /**
  * 最小缩放比例，最大为100%
  */
 private void minZoom() {
  minScaleR = Math.min(
    (float) dm.widthPixels / (float) bitmap.getWidth(),
    (float) dm.heightPixels / (float) bitmap.getHeight());
  if (minScaleR < 1.0) {
   matrix.postScale(minScaleR, minScaleR);
  }
 }
 private void center() {
  center(true, true);
 }
 /**
  * 横向、纵向居中
  */
 protected 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) {
   // 图片小于屏幕大小，则居中显示。大于屏幕，上方留空则往上移，下方留空则往下移
   int screenHeight = dm.heightPixels;
   if (height < screenHeight) {
    deltaY = (screenHeight - height) / 2 - rect.top;
   } else if (rect.top > 0) {
    deltaY = -rect.top;
   } else if (rect.bottom < screenHeight) {
    deltaY = imgView.getHeight() - rect.bottom;
   }
  }
  if (horizontal) {
   int screenWidth = dm.widthPixels;
   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);
 }
 /**
  * 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);
 }
}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 android:layout_gravity="center" >
 <ImageView
  android:id="@+id/imag"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:layout_gravity="center"
  android:scaleType="matrix" >
 </ImageView>
</FrameLayout>