android 图片的浏览、缩放、拖动和自动居中示例

/** * 图片浏览、缩放、拖动、自动居中 */
public class ImageTouch 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.main);
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
bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);// 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，下放留空则往下移
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>