Engine中如何监控IPageLayoutControl中地图范围发生变化的事件？

private void extentUpdateToolStripMenuItem_Click(object sender, EventArgs e) 

{ 

IActiveView activeView = axPageLayoutControl1.ActiveView.FocusMap as IActiveView; 

m_transformEvents = activeView.ScreenDisplay.DisplayTransformation as ITransformEvents_Event; 

m_transformEvents.VisibleBoundsUpdated += new ITransformEvents_VisibleBoundsUpdatedEventHandler(extentUpated); 

} 

private void extentUpated(IDisplayTransformation sender, bool sizeChanged) 

{ 



}