Customize UINavigationbar 和 改变图片大小

    //加载NavigationBar的背景图片
    UINavigationController *navController = [self navigationController];
    UINavigationBar *navBar = [navController navigationBar];
    CGSize navSize = CGSizeMake(navBar.frame.size.width, navBar.frame.size.height);
    UIImage *scaledImage = [self scaleToSize:[UIImage imageNamed:@"wall-header_title.png"] size:navSize];
    [navBar setBackgroundImage:scaledImage forBarMetrics: UIBarMetricsDefault];

    //改变 rightBarButtonItem 形状
    UIBarButtonItem * item = [[UIBarButtonItem alloc] initWithCustomView:[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"btn_header_update_normal.png"]]];
    self.navigationItem.rightBarButtonItem = item;

- (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)newsize{
    // 创建一个bitmap的context
    // 并把它设置成为当前正在使用的context
    UIGraphicsBeginImageContext(newsize);
    // 绘制改变大小的图片
    [img drawInRect:CGRectMake(0, 0, newsize.width, newsize.height)];
    // 从当前context中创建一个改变大小后的图片
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    // 使当前的context出堆栈
    UIGraphicsEndImageContext();
    // 返回新的改变大小后的图片
    return scaledImage; 
}


// BackButton页面
    if([self.navigationController.viewControllers objectAtIndex:0] != self)
    {
        UIButton *backButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
        [backButton setImage:[UIImage imageNamed:@"btn_header_prev_normal.png"] forState:UIControlStateNormal];
        [backButton setShowsTouchWhenHighlighted:TRUE];
        [backButton addTarget:self action:@selector(popViewControllerWithAnimation) forControlEvents:UIControlEventTouchDown];
        UIBarButtonItem *barBackItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
        self.navigationItem.hidesBackButton = TRUE;
        self.navigationItem.leftBarButtonItem = barBackItem;
    }