Software Engineering and Computer Games

6.4. Updating the views

The UpdateAllViews( CView* pSender, int lHint, CObject* pHint) method generates calls to the CPopView::OnUpdate( CView* pSender, int lHint, CObject* pHint) method for each open view, passing on the same arguments.

A minimal version of the OnUpdate method could look like this.

void CPopView::OnUpdate(CView* pSender, LPARAM lHint, CObject* pHint) 
{ 
    Invalidate(); /* Enqueue a message asking Windows to call OnDraw 
        for this view. */ 
} 

Invalidate produces a call to OnDraw, which is where the critters get drawn to the active window.

But what about the three arguments to UpdateAllViews and OnUpdate ? It’s possible for a view to initiate a call to UpdateAllViews with a line like this: GetDocument()->UpdateAllViews. This trick ...