iphone从AppDelegate设置RightBarButtonItem

Question

我试图从 appDelegate 中设置导航栏的右侧按钮，代码编译并执行时没有错误，但按钮没有出现。

如有任何帮助，我们将不胜感激。

谢谢。

NSAutoreleasePool *apool = [[NSAutoreleasePool alloc] init];
    UIActivityIndicatorView *aiv = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
    UIBarButtonItem *activityButtonItem = [[UIBarButtonItem alloc] initWithCustomView:aiv];
    [aiv startAnimating]; 
    [aiv release];


    [self.navigationController.navigationItem setRightBarButtonItem:activityButtonItem animated:YES];
    [activityButtonItem release];
    [apool release];

Answer 1

首先一些提示。

在短时间内创建大量自动释放对象的情况下，您可以使用NSAutoReleasePool，例如循环中。引用苹果的话:

If your application creates a lot of temporary autoreleased objects within the event loop, however, it may be beneficial to create “local” autorelease pools to help to minimize the peak memory footprint.

由于您没有创建任何自动释放对象，因此没有必要拥有NSAutoReleasePool。

通常，您会将用于设置导航栏按钮的代码放在应响应按钮的 UIViewController 的 viewDidLoad 中。当 UINavigationController 将新的 UIViewController 推送到其堆栈时，它将向 Controller 询问应显示的任何按钮。

假设您的 UINavigationController 的 Root View Controller 是默认生成的 RootViewController。然后你应该将代码放在RootViewController的viewDidLoad中。或者也许在 viewDidAppear: 中，因为您正在为插入设置动画。

UIActivityIndicatorView *aiv = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
UIBarButtonItem *activityButtonItem = [[UIBarButtonItem alloc] initWithCustomView:aiv];
[aiv startAnimating]; 
[aiv release];

[self.navigationItem setRightBarButtonItem:activityButtonItem animated:YES];
[activityButtonItem release];

如果您确实必须在应用程序委托(delegate)中包含可以通过以下方式完成的代码:

UIActivityIndicatorView *aiv = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
UIBarButtonItem *activityButtonItem = [[UIBarButtonItem alloc] initWithCustomView:aiv];
[aiv startAnimating]; 
[aiv release];

UIViewController *rootController = [self.navigationController topViewController];
rootController.navigationItem.rightBarButtonItem = activityButtonItem;    
[activityButtonItem release];