Re: Redraw view in setFrame?

[Dr. H. Nikolaus Schaller]

Hi,

Am 31.10.2013 um 03:07 schrieb Lundberg, Johannes:

> Hi All!
> 
> I've been playing with the NSViewAnimation class and discovered that the view 
> is not redrawn between animation steps.
> 
> First I was thinking that a call could be made to [_target setNeedsDisplay] 
> at each animation step in NSViewAnimation.m but wouldn't it be better to do 
> that in NSView's setFrame?

https://developer.apple.com/library/mac/documentation/cocoa/reference/applicationkit/classes/NSView_Class/Reference/NSView.html#//apple_ref/occ/instm/NSView/setFrame:

"It neither redisplays the receiver nor marks it as needing display. You must 
do this yourself with display or setNeedsDisplay:."

> 
> Whenever you change the frame of a view don't you want it to always redraw 
> anyway?

Not necessarily. A view may be hidden. Or resized several times. Well, a 
setNeedsDisplay:YES wouldn't do any harm - an invisible view isn't drawn even 
if set to needsDisplay... But it costs calculation time (especially for rotated 
and scaled views).

> 
> This seems to be the case on Cocoa. I've attached a Xcode 5 project example 
> app that shows that view is redrawn without calling setNeedsDisplay when 
> changing frame. (not sure if the same applies to Cocoa Touch though...)

It may be done but you should never rely on it in your code.

> 
> Another thing is that when moving or shrinking a view setNeedsDisplay needs 
> to be called before and after the new frame is set otherwise the area of the 
> old frame view won't be cleared.
> 
> Have this kind of code in your app is not so elegant.
> 
> [view setNeedsDisplay:YES];
> view.frame = newFrame;
> [view setNeedsDisplay:YES];
> 
> I propose that we move that into NSView. I made a dirty fix that may not be 
> the optimal way to do it but it shows what I want to do with this proposal.
> 
> 
> in NSView's - (void) setFrame: (NSRect)frameRect i added two calls to 
> setNeedsDisplay like this:
> 
>   if (changedSize == YES || changedOrigin == YES)
>     {
>       [self setNeedsDisplay:YES];

[[self superview] setNeedsDisplayInRect:oldFrame] would be more correct IMHO.

>       [self _setFrameAndClearAutoresizingError: frameRect];
>       [self setNeedsDisplay:YES];
>       ......
> 
> What do you guys think?

IMHO it could be done, just in case that some application is not doing it 
correctly. But this may help programmers to do it not correctly and writing 
wrong code which makes porting to other *STEP platforms fail.

Just my 2ct.

-- hns