Android编程实现图片的浏览、缩放、拖动和自动居中效果

本文实例讲述了Android编程实现图片的浏览、缩放、拖动和自动居中效果的方法。分享给大家供大家参考，具体如下：

Touch.java

/**
* 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);
}
}

scale.xml

<?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>

希望本文所述对大家Android程序设计有所帮助。