Question

I would like to set an image background to the navigation bar on my iphone app. Most solutions suggest using drawRect in a category like:

@implementation UINavigationBar (CustomImage)
- (void)drawRect:(CGRect)rect {
    UIImage *image = [UIImage imageNamed: @"NavigationBar.png"];
    [image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
}
@end

However, Apple does not recommend this. Any other suggestion?

Thx for helping,

Stephane

Answer 1

Apple strongly advise us to use subclasses rather than categories (WWDC 2011, Session 123).

Create a subclass which implements the drawRect: method and set the class of your navigation bar to your custom class:

• if you’re working in Interface Builder, change the class in the inspector
• if you create a stand-alone navigation bar (without nav controller), instantiate your custom class
• if you create a navigation controller programmatically, you could take advantage of the ObjC runtime.

Class switch at runtime:

 #import <objc/runtime.h>
 ...
 object_setClass(theNavController.navigationBar, [CustomNavigationBar class]);

You should also avoid using [UIImage imageNamed:...] each time in drawRect: as it might have an impact on performance (for animations). Cache it in an ivar:

 if (!bgImage) {
     bgImage = [[UIImage imageNamed:@"NavigationBar.png"] retain];
 }
 [bgImage drawInRect:...];

(and release it in dealloc)

Note: As iOS 5 is still under NDA, I can’t mention how you could easily add a background image. Check out the docs for UINavigationBar.