ImageView 缩放

 <ImageView
                android:id="@+id/imageview"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"                
                android:src="@drawable/zixun"
                android:scaleType="matrix"
                />


关键点：缩放的内容不能是图片的背景，一定要是图片的内容

public class HelpActivity 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();

    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.help);
        ImageView view = (ImageView) findViewById(R.id.imageview);
//        view.setImageResource(R.drawable.icon);
        view.setOnTouchListener(mOnTouchListener);
    }

    OnTouchListener mOnTouchListener = new OnTouchListener()
    {
        public boolean onTouch(View v, MotionEvent event)
        {
            Trace.Log("------------------"+event.toString());
            ImageView view = (ImageView) v;
            switch (event.getAction() & MotionEvent.ACTION_MASK)
            {
            case MotionEvent.ACTION_DOWN:
                savedMatrix.set(matrix);
                start.set(event.getX(), event.getY());
                mode = DRAG;
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP:
                mode = NONE;
                break;
            // 多点触控
            case MotionEvent.ACTION_POINTER_DOWN:
                oldDist = spacing(event);
                if (oldDist > 10f)
                {
                    savedMatrix.set(matrix);
                    midPoint(mid, event);
                    mode = ZOOM;
                }
                break;
            case MotionEvent.ACTION_MOVE:
                if (mode == DRAG)
                {
                    matrix.set(savedMatrix);
                    matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);
                }
                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);
                        Trace.Log("------------------"+newDist);
                    }
                }
                break;
            }

            view.setImageMatrix(matrix);
//            view.invalidate();
            return true;
        }

    };

    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);
    }

    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);
    }

    public void onClickBack(View view)
    {
        backToCardSelect();
    }    
}

ImageVIew 需要在最上面一层，否则可能不会生效