初学Android,手势缩放图片(四十八)

下面的例子是用手势来缩放图片，手指往右划是放大，往左是缩小

下面效果在手机模拟器上呈现的只能是鼠标光标的划动了

package WangLi.IO.GestureZoom;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.view.GestureDetector;
import android.view.GestureDetector.OnGestureListener;
import android.view.MotionEvent;
import android.widget.ImageView;

public class GestureZoom extends Activity implements OnGestureListener
{
	GestureDetector detector;
	ImageView imageView;
	//初始的图片资源
	Bitmap bitmap;
	//定义图片的宽,高
	int width,height;
	//记录当前的缩放比
	float currentScale = 1;
	//控制图片缩放的Matrix对象
	Matrix matrix;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //创建手势检测器
        detector = new GestureDetector(this);
        imageView = (ImageView)findViewById(R.id.show);
        matrix = new Matrix();
        //获取被缩放的源图片
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.hotel);
        //获得位图宽
        width = bitmap.getWidth();
        //获得位图高
        height = bitmap.getHeight();
        //设置ImageView初始化时显示的图片
        imageView.setImageBitmap(BitmapFactory.decodeResource(
        		getResources(), R.drawable.hotel));
    }
    @Override
    public boolean onTouchEvent(MotionEvent me)
    {
    	//将Activity上的触碰事件交给GestureDetector处理
    	return detector.onTouchEvent(me);
    }
    
	@Override
	public boolean onDown(MotionEvent arg0) {
		// TODO Auto-generated method stub
		return false;
	}
	@Override
	public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
			float velocityY) {
		// TODO Auto-generated method stub
		velocityX = velocityX > 4000 ? 4000 : velocityX;
		velocityX = velocityX < -4000 ? -4000 : velocityX;
		//根据手势的速度来计算缩放比,如果velocity > 0,放大图像,否则缩小图像
		currentScale += currentScale * velocityX / 4000.0f;
		//保证currentScale不会等于0
		currentScale = currentScale > 0.01 ? currentScale : 0.01f;
		//重置Matrix
		matrix.reset();
		//缩放Matrix
		matrix.setScale(currentScale, currentScale ,160, 200);
		BitmapDrawable tmp = (BitmapDrawable)imageView.getDrawable();
		//如果图片还未回收,先强制回收该图片
		if(!tmp.getBitmap().isRecycled())
		{
			tmp.getBitmap().recycle();
		}
		//根据原始位图和Matrix创建新图片
		Bitmap bitmap2 = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix,true);
		imageView.setImageBitmap(bitmap2);
		return false;
	}
	@Override
	public void onLongPress(MotionEvent e) {
		// TODO Auto-generated method stub
	}
	@Override
	public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
			float distanceY) {
		// TODO Auto-generated method stub
		return false;
	}
	@Override
	public void onShowPress(MotionEvent e) {
		// TODO Auto-generated method stub
	}
	@Override
	public boolean onSingleTapUp(MotionEvent e) {
		// TODO Auto-generated method stub
		return false;
	}
}