UINavigationItem setLeftBarButtonItems Delay

Question

我有一个相当混乱的问题：在我的应用程序中，我正在检查网络连接，如果用户没有连接到互联网，我会在导航栏中显示一个红色的小感叹号。

用于显示感叹号的代码如下所示：

    - (void)showConnectivityMessage
{
    UIBarButtonItem *exclamationMark = [[UIBarButtonItem alloc]initWithTitle:@"!" style:UIBarButtonItemStyleDone target:self action:@selector(showConnectivityInfo)];
    [exclamationMark setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor redColor],
                                              NSFontAttributeName:[UIFont boldSystemFontOfSize:22]} forState:UIControlStateNormal];

    NSMutableArray *items = [NSMutableArray arrayWithArray:self.navigationItem.leftBarButtonItems];
    [items addObject:exclamationMark];
    [self.navigationItem setLeftBarButtonItems:items];
    NSLog(@"Should show exclamation mark!");

}

方法调用正确，我可以看到输出"Should show exclamation mark!"。现在，奇怪的是，新的导航项实际出现还需要大约 20 秒...

有谁知道这种延迟可能来自哪里？任何解决错误的帮助将不胜感激！

Answer 1

有些代码阻塞了主线程。试试这个。可能对你有帮助

- (void)showConnectivityMessage
{
    dispatch_async(dispatch_get_main_queue(), ^{
        UIBarButtonItem *exclamationMark = [[UIBarButtonItem alloc]initWithTitle:@"!" style:UIBarButtonItemStyleDone target:self action:@selector(showConnectivityInfo)];
        [exclamationMark setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor redColor],
                                                  NSFontAttributeName:[UIFont boldSystemFontOfSize:22]} forState:UIControlStateNormal];

        NSMutableArray *items = [NSMutableArray arrayWithArray:self.navigationItem.leftBarButtonItems];
        [items addObject:exclamationMark];
        [self.navigationItem setLeftBarButtonItems:items];
        NSLog(@"Should show exclamation mark!");
    });

}

Answer 2

每次您在 UI 中看到类似的延迟，那是因为您还没有从主线程更新 UI。始终仅从主线程更新 UI。

dispatch_async(dispatch_get_main_queue(), ^{
    UIBarButtonItem *exclamationMark = [[UIBarButtonItem alloc]initWithTitle:@"!" style:UIBarButtonItemStyleDone target:self action:@selector(showConnectivityInfo)];
   [exclamationMark setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor redColor],
                                          NSFontAttributeName:[UIFont boldSystemFontOfSize:22]} forState:UIControlStateNormal];

    NSMutableArray *items = [NSMutableArray arrayWithArray:self.navigationItem.leftBarButtonItems];
    [items addObject:exclamationMark];
    [self.navigationItem setLeftBarButtonItems:items];
    NSLog(@"Should show exclamation mark!");
}

UINavigationItem setLeftBarButtonItems Delay

UINavigationItem setLeftBarButtonItems Delay

objective-c

uinavigationitem

ios