Iphone – Calling setNeedsDisplay on a UIView from another class

drawrectiphonequartz-graphicsuiview

I have a UIView subclass that I manipulate a lot of graphics on based on touches. All the [self setNeedsDisplay] calls seem to be fine.

However, I used an instance variable pointer to my same UIView subclass instance, and then tried manipulating it and then calling [UIViewSubClass setNeedsDisplay] from another UIView class, and DrawRect is never being called. Are there restrictions to where you can call setNeedsDisplay from?

(This method is called when a button is clicked on another UIView subclass. The method is being called, but not DrawRect)

-(IBAction)loadGrid2;
{
    tempSoundArray = musicGridView1.soundArray;
    [musicGridView1.soundArray setButtonArrayToNull];
    [musicGridView1 setNeedsDisplay];
    musicGridView1.soundArray = tempSoundArray;
    NSLog(@"loadGrid2 was called");
}

Best Answer

drawRect: will only be called when it makes sense; ie, the view must be visible, onscreen, and dirty. Is your drawRect: ever called? It should be called when the view is first brought onscreen as well.

Related Solutions

Cocoa-touch – the most robust way to force a UIView to redraw

The guaranteed, rock solid way to force a UIView to re-render is [myView setNeedsDisplay]. If you're having trouble with that, you're likely running into one of these issues:

You're calling it before you actually have the data, or your -drawRect: is over-caching something.
You're expecting the view to draw at the moment you call this method. There is intentionally no way to demand "draw right now this very second" using the Cocoa drawing system. That would disrupt the entire view compositing system, trash performance and likely create all kinds of artifacting. There are only ways to say "this needs to be drawn in the next draw cycle."

If what you need is "some logic, draw, some more logic," then you need to put the "some more logic" in a separate method and invoke it using -performSelector:withObject:afterDelay: with a delay of 0. That will put "some more logic" after the next draw cycle. See this question for an example of that kind of code, and a case where it might be needed (though it's usually best to look for other solutions if possible since it complicates the code).

If you don't think things are getting drawn, put a breakpoint in -drawRect: and see when you're getting called. If you're calling -setNeedsDisplay, but -drawRect: isn't getting called in the next event loop, then dig into your view hierarchy and make sure you're not trying to outsmart is somewhere. Over-cleverness is the #1 cause of bad drawing in my experience. When you think you know best how to trick the system into doing what you want, you usually get it doing exactly what you don't want.

Ios – Giving UIView rounded corners

Try this

#import <QuartzCore/QuartzCore.h> // not necessary for 10 years now  :)

...

view.layer.cornerRadius = 5;
view.layer.masksToBounds = true;

Note: If you are trying to apply rounded corners to a UIViewController's view, it should not be applied in the view controller's constructor, but rather in -viewDidLoad, after view is actually instantiated.

Best Answer

Related Solutions

Cocoa-touch – the most robust way to force a UIView to redraw

Ios – Giving UIView rounded corners

Related Topic