如何实现Imageview图片进行缩放

几个重要知识点：
1、布局文件中android:scaleType=”matrix” 设置图片动态缩放
2、matrix.postTranslate(dx,dy); 平移图片 matrix.postScale(sx,sy,p.x,p.y); 缩放图片
3、两点的中点、距离计算方式，限制缩放范围函数，在指定区域内移动图片方法
(以下代码网上很多地方有类似的，仅供参考)

public class Main extends Activity
{
private static final int NONE = 0;
private static final int DRAG = 1;
private static final int ZOOM = 2;

private int mode = NONE;  
private float oldDist;  
private Matrix matrix = new Matrix();  
private Matrix savedMatrix = new Matrix();  
private PointF start = new PointF();  
private PointF mid = new PointF();  

ImageView view;  
Bitmap bitmap;  
DisplayMetrics dm;  
float minScaleR=0.1f;  //最少缩放比例  
static final float MAX_SCALE = 4f; //最大缩放比例  
float dist = 1f;  

@Override  
public void onCreate(Bundle savedInstanceState)  
{  
    super.onCreate(savedInstanceState);  
    setContentView(R.layout.main);  
    view = (ImageView) findViewById(R.id.image_view);  
    bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);  

    dm = new DisplayMetrics();  
    getWindowManager().getDefaultDisplay().getMetrics(dm); //获取分辨率  


    matrix.setScale(minScaleR, minScaleR); //开始先缩小  
    matrix.postTranslate(120, 120);     //图片的位置相对于imageview的左上角往右往下各偏移120个像素  
    view.setImageMatrix(matrix);  

    view.setOnTouchListener(new OnTouchListener()  
    {  
        @Override  
        public boolean onTouch(View v, MotionEvent event)  
        {  
            ImageView view = (ImageView) v;  
            switch (event.getAction() & MotionEvent.ACTION_MASK)  
            {  
            case MotionEvent.ACTION_DOWN:  //单点  
                Toast.makeText(Main.this, bitmap.getWidth()+"*"+bitmap.getHeight(), Toast.LENGTH_LONG).show();  
                savedMatrix.set(matrix);  
                start.set(event.getX(), event.getY());  
                mode = DRAG;  
                break;  
            case MotionEvent.ACTION_UP:  //单点弹起  
            case MotionEvent.ACTION_POINTER_UP:  //多点弹起  
                mode = NONE;  
                break;  
            case MotionEvent.ACTION_POINTER_DOWN:  //多点  
                oldDist = spacing(event);  
                if (oldDist > 10f)  
                {  
                    savedMatrix.set(matrix);  
                    midPoint(mid, event);  
                    mode = ZOOM;  
                }  
                break;  
            case MotionEvent.ACTION_MOVE: //按下且在拖动  
                if (mode == DRAG)  
                {  
                    matrix.set(savedMatrix);  
                    matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);  //xy方向都可以拖动  
                    //matrix.postTranslate(event.getX() - start.x,0); //只在x轴方向拖动 即左右拖动  上下不动  
                    //matrix.postTranslate(0,event.getY() - start.y);  //只在y轴方向拖动 即上下拖动  左右不动  
                }  
                else if (mode == ZOOM)  
                {  
                    float newDist = spacing(event);  
                    if (newDist > 10f)  
                    {  
                        matrix.set(savedMatrix);  
                        float scale = newDist / oldDist;  
                        matrix.postScale(scale, scale, mid.x, mid.y);  
                    }  
                }  
                break;  
            }  

            view.setImageMatrix(matrix);  

            CheckScale();  //限制缩放范围  
            center();  //居中控制  

            return true;  
        }  


        //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);  
        }  
    });  
}  

//限制最大最小缩放比例    
protected void CheckScale()  
{  
    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);  
        }  
    }  
}  

//自动居中  左右及上下都居中  
protected void center()  
{  
    center(true,true);  
}  

private 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)  
    {  
        //int screenHeight = dm.heightPixels;  //手机屏幕分辨率的高度  
        int screenHeight = 400;  
        if (height < screenHeight)  
        {  
            deltaY = (screenHeight - height)/2 - rect.top;  
        }else if (rect.top > 0)  
        {  
            deltaY = -rect.top;  
        }else if (rect.bottom < screenHeight)  
        {  
            deltaY = view.getHeight() - rect.bottom;  
        }  
    }  

    if (horizontal)  
    {  
        //int screenWidth = dm.widthPixels;  //手机屏幕分辨率的宽度  
        int screenWidth = 400;  
        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);  
}  

}