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Re: Notification when a view goes offscreen?

On Jan 27, 2004, at 8:16 AM, Nicholas Francis wrote:
Hi guys...

In our app, I'm pulling complete view hierarchies off-screen, and replacing them with something else. Is there a way for a view to get notified when it goes offscreen (like in its parent being -removeFromSuperview)?

NSView provides stub methods that get invoked when a view's window or superview changes:

- (void)viewWillMoveToWindow:(NSWindow *)newWindow;
- (void)viewDidMoveToWindow;
- (void)viewWillMoveToSuperview:(NSView *)newSuperview;
- (void)viewDidMoveToSuperview;

You can override these in a subclass to receive notice of such occurrences.

This covers views "going offscreen" in the way that I gather you are concerned with here (due to swapping of views out of and into a window via -removeFromSuperview and -addSubview: operations). If you were interested in other ways that a view can "go offscreen" (e.g. due to its window being closed or moved to another screen), you'd also want to take a look at the notifications declared in NSWindow.h. For the NSView -setHidden: API introduced in Panther, there is currently no notification mechanism, but one could simply override -setHidden: to invoke super's implementation and then perform whatever actions are needed:

- (void)setHidden:(BOOL)hiding {
[super setHidden:hiding];
// Now do whatever we need to in response to this change...
}

Hope this helps.

Troy Stephens
Cocoa frameworks
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 >Notification when a view goes offscreen? (From: Nicholas Francis <email@hidden>)



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