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>