如何在不使用drawRect类别的情况下将图像设置为导航栏背景？

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.

Answer 2

Tested Code : 100 % works

in ur ViewDidLoad

UIImageView *iv=[[UIImageView alloc]initWithImage:[UIImage imageNamed:@"urNavBarImage.png"]];

self.navigationItem.titleView = iv;

[iv release];

NOTE: urNavBarImage should be exact size of Navigation Bar. Like this u can change every Viewcontroller Navigation bar.

Answer 3

I have created a custom category for UINavigationBar as follows

UINavigationBar+CustomImage.h

#import <UIKit/UIKit.h>

@interface UINavigationBar (CustomImage)
    - (void) setBackgroundImage:(UIImage*)image;
    - (void) clearBackgroundImage;
    - (void) removeIfImage:(id)sender;
@end

UINavigationBar+CustomImage.m

#import "UINavigationBar+CustomImage.h"

@implementation UINavigationBar (CustomImage)

- (void) setBackgroundImage:(UIImage*)image {
    if (image == NULL) return;
    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
    imageView.frame = CGRectMake(110,5,100,30);
    [self addSubview:imageView];
    [imageView release];
}

- (void) clearBackgroundImage {
    NSArray *subviews = [self subviews];
    for (int i=0; i<[subviews count]; i++) {
        if ([[subviews objectAtIndex:i]  isMemberOfClass:[UIImageView class]]) {
        [[subviews objectAtIndex:i] removeFromSuperview];
    }
   }    
}

@end

I invoke it from my UINavigationController

[[navController navigationBar] performSelectorInBackground:@selector(setBackgroundImage:) withObject:image];