Objective c 点击项目时，选项卡栏上的setBackgroundImage不起作用

我可以设置一次背景，但在那之后它再也不会改变。我看过所有关于stackoverflow的例子。代码示例看起来总是一样的。我已经设置了代理。图像都很好。我已经将它们一个接一个地设置为默认图像，并将显示。但在应用程序完成启动后，背景不再发生任何变化

这是我的密码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [self customizeInterface];

    // Override point for customization after application launch.
    self.tabController = (UITabBarController *)self.window.rootViewController;
    self.tabController.delegate = self;
...
}

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    int tabitem = self.tabController.selectedIndex;
    NSLog(@"tabitem: %i", tabitem);
    [self switchTabBarImage:tabitem];
    //[[tabController objectAtIndex:tabitem] popToRootViewControllerAnimated:YES];
}

- (void)switchTabBarImage:(int)selectedIndex
{
    NSLog(@"selected: %i", selectedIndex);
    if (selectedIndex == 0) {
        NSLog(@"0");
        UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-1.png"];
        [[UITabBar appearance] setBackgroundImage:tabBarBackground];
    }
    if (selectedIndex == 1) {
        NSLog(@"1");
        UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-2.png"];
        [[UITabBar appearance] setBackgroundImage:tabBarBackground];
    }
    if (selectedIndex == 2) {
        NSLog(@"2");
        UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-3.png"];
        [[UITabBar appearance] setBackgroundImage:tabBarBackground];
    }
    if (selectedIndex == 3) {
        NSLog(@"3");
        UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-4.png"];
        [[UITabBar appearance] setBackgroundImage:tabBarBackground];
    }
}

- (void)customizeInterface
{

    UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-1.png"];
    [[UITabBar appearance] setBackgroundImage:tabBarBackground];

    UIImage *selectionIndicator = [UIImage imageNamed:@"tabbar-icon-clean.png"];
    [[UITabBar appearance] setSelectionIndicatorImage:selectionIndicator];

}

调试器显示：

2012-11-13 02:42:06.147 soundapp[9060:c07] tabitem: 1
2012-11-13 02:42:06.148 soundapp[9060:c07] selected: 1
2012-11-13 02:42:06.148 soundapp[9060:c07] 1
2012-11-13 02:42:07.739 soundapp[9060:c07] tabitem: 2
2012-11-13 02:42:07.739 soundapp[9060:c07] selected: 2
2012-11-13 02:42:07.740 soundapp[9060:c07] 2

---

我搜索了几个小时，也不明白为什么它只工作一次。有人看到我的代码中有错误吗？

又过了一个小时，我在网上的其他地方找到了解决方案(http://felipecypriano.com/2012/02/27/how-to-customize-uitabbar-on-ios-5/)

我真的不明白为什么有两种不同的方式来改变背景。令人困惑的是，这两个不同的代码行只在不同的地方工作。我不明白。但现在它起作用了

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    int tabitem = self.tabController.selectedIndex;
    NSLog(@"tabitem: %i", tabitem);
    [self switchTabBarImage:tabitem];
    //[[tabController objectAtIndex:tabitem] popToRootViewControllerAnimated:YES];
}

- (void)switchTabBarImage:(int)selectedIndex
{

    switch (selectedIndex) {
        case 0:
            [[[self tabController] tabBar] setBackgroundImage:[UIImage imageNamed:@"tabbar-1.png"]];
            break;
        case 1:
            [[[self tabController] tabBar] setBackgroundImage:[UIImage imageNamed:@"tabbar-2.png"]];
            break;
        case 2:
            [[[self tabController] tabBar] setBackgroundImage:[UIImage imageNamed:@"tabbar-3.png"]];
            break;
        case 3:
            [[[self tabController] tabBar] setBackgroundImage:[UIImage imageNamed:@"tabbar-4.png"]];
            break;
    }
}

- (void)customizeInterface
{

    UIImage *tabBarBackground = [UIImage imageNamed:@"tabbar-1.png"];
    [[UITabBar appearance] setBackgroundImage:tabBarBackground];

    UIImage *selectionIndicator = [UIImage imageNamed:@"tabbar-icon-clean.png"];
    [[UITabBar appearance] setSelectionIndicatorImage:selectionIndicator];

}