自定义NavigationBar、NavgationItem

一、下面是自定义NavigationBar，可以随意放置nav的背景图，同时可以兼容iOS5和iOS4及以前的版本，主要是重写系统的nav，用到了类别。这是第一次用类别，收获不小。@implementation UINavigationBar (CustomBackground)      //重写navbar
- (UIImage *)barBackground{
      return [UIImage imageNamed:@"1.png"];
}
- (void)didMoveToSuperview{
      //iOS5 only
      if ([self respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)])
      {
              [self setBackgroundImage:[self barBackground] forBarMetrics:UIBarMetricsDefault];
      }
}
//this doesn't work on iOS5 but is needed for iOS4 and earlier
- (void)drawRect:(CGRect)rect{
      //draw image
      [[self barBackground] drawInRect:rect];
      //[[self backItem] setBackBarButtonItem:<#(UIBarButtonItem *)#>]
}
@end
二、自定义nav上面的按钮，左右各示范一个，用到了IBarButtonItem的initWithCustomView方法，设置按钮的背景图片       //返回按钮  
        UIButton *backBtn = [[UIButton alloc] initWithFrame:CGRectMake(0.0, 100.0, 62.0, 29.0)];
        [backBtn setTitle:@"返回" forState:UIControlStateNormal];
        [backBtn setBackgroundImage:[UIImage imageNamed:@"top_btn_bg.png"] forState:UIControlStateNormal];
        [backBtn addTarget:self action:@selector(backAction) forControlEvents:UIControlEventTouchUpInside];
        UIBarButtonItem *backBarBtn = [[UIBarButtonItem alloc] initWithCustomView:backBtn];
        self.navigationItem.leftBarButtonItem=backBarBtn;
        [backBtn release];
        [backBarBtn release];
        //首页按钮
        UIButton *indexBtn = [[UIButton alloc] initWithFrame:CGRectMake(250.0, 100.0, 62.0, 29.0)];
        [indexBtn setTitle:@"首页" forState:UIControlStateNormal];
        [indexBtn setBackgroundImage:[UIImage imageNamed:@"back_home.png"] forState:UIControlStateNormal];
        [indexBtn addTarget:self action:@selector(goIndex) forControlEvents:UIControlEventTouchUpInside];
        UIBarButtonItem *indexBarBtn = [[UIBarButtonItem alloc] initWithCustomView:indexBtn];
        self.navigationItem.rightBarButtonItem=indexBarBtn;
        [indexBtn release];
        [indexBarBtn release];
三、下面的方法可以为nav更换背景图片  ios5上面就不需要了，因为有了新的方法         UIImageView* imageview=[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"nav_bg.png"]];
        imageview.frame=CGRectMake(0,0,320,44);
        imageview.tag=1000;
        [self.navigationController.navigationBar addSubview:imageview];
        [imageview release];