Ограничение перетаскивания ImageView в Android

У меня есть ImageView в макете, и я установил OnTouchListener в ImageView, чтобы перетащить ImageView. Он работает отлично. Моя проблема в том, как я могу предотвратить перемещение ImageView за пределы диапазона макета?

Это мой код:

Класс активности:

public class RepositionTestActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.reposition_test_layout);
        ImageView imageView = (ImageView)findViewById(R.id.android);
        imageView.setOnTouchListener(new Touch());
    }
}

Сенсорный класс:

public class Touch implements OnTouchListener {

    private static final int NONE = 0;
    private static final int DRAG = 1;
    private static final int ZOOM = 2;

    private static final float MIN_ZOOM = 1f;
    private static final float MAX_ZOOM = 5f;

    private Matrix matrix = new Matrix();
    private Matrix savedMatrix = new Matrix();

    private PointF start = new PointF();
    private PointF mid = new PointF();

    private int mode = NONE;
    private float oldDistance = 1f;

    public boolean onTouch(View view, MotionEvent event) {
        ImageView imageView = (ImageView)view;

        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_POINTER_DOWN:
                oldDistance = spacing(event);
                if(oldDistance > 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() - start.x, event.getY() - start.y);
                }
                else if(mode == ZOOM) {
                    float newDistance = spacing(event);
                    if(newDistance > 10f) {
                        matrix.set(savedMatrix);
                        float scale = newDistance / oldDistance;
                        float[] values = new float[9];
                        matrix.getValues(values);
                        float currentScale = values[Matrix.MSCALE_X];
                        if(scale * currentScale > MAX_ZOOM) 
                            scale = MAX_ZOOM / currentScale;
                        else if (scale * currentScale < MIN_ZOOM)
                            scale = MIN_ZOOM / currentScale;
                        matrix.postScale(scale, scale, mid.x, mid.y);
                    }
                }
                break;
        }
        imageView.setImageMatrix(matrix);
        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) {
        point.set((event.getX(0) + event.getX(1)) / 2, (event.getY(0) + event.getY(1)) / 2);
    }

}

Макет xml:

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/reposition_test_layout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <ImageView
        android:id="@+id/android"
        android:src="@drawable/android"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:scaleType="matrix"
        android:contentDescription="@string/android_description" >
    </ImageView>

</LinearLayout>