//- (void)setBackgroundImage:(UIImage *)backgroundImage forBarMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;

-(id)init

{

    self=[super init];

    if(self)

    {

        UINavigationBar *navBar=[self navigationBar];

        if([navBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)])

        {

//如果是IOS5

            [[UINavigationBar appearance]setBackgroundImage:[UIImage imageNamed:@"NavBar.png"] forBarMetrics:UIBarMetricsDefault];

        }

        else

        {

            UIImageView *imgView=(UIImageView*)[navBar viewWithTag:NAVBARIMAGETAG];

            if(imgView==nil)

            {

                imgView=[[UIImageView alloc]initWithFrame:CGRectMake(0, 0,navBar.frame.size.width, navBar.frame.size.height)];

                [imgView setImage:[UIImage imageNamed:@"NavBar.png"]];

                [navBar insertSubview:imgView atIndex:0];

                [imgView release];

            }

        }

    }

    return self;

}