由于NSUserDefaultsDidChangeNotification，后台线程的UI更改 [英] UI changes on background thread due to NSUserDefaultsDidChangeNotification

问题描述

我正在调试一个问题，偶尔会导致我的应用程序崩溃，并在崩溃报告中显示 WebTryThreadLock 消息。看起来应用程序崩溃了，因为 NSUserDefaultsDidChangeNotification 正在后台线程上发送和接收。我在收到通知时进行了UI更改，并了解强烈建议在后台线程上进行UI更改。

I am debugging an issue that occasionally causes my app to crash with a WebTryThreadLock message in the crash report. It looks like the app is crashing because the NSUserDefaultsDidChangeNotification is being sent and received on a background thread. I make UI changes when the notification is received and understand that making UI changes on a background thread is highly advised against.

如果 NSUserDefaultsDidChangeNotification 有时（如果不是总是）在后台线程上发送，处理这个问题的最佳方法是什么？类似以下内容似乎过多但可能是必要的。

If NSUserDefaultsDidChangeNotification is sometimes (if not always) sent on a background thread, what is the best way to handle this? Something like the following seems excessive but potentially necessary.

[[NSNotificationCenter defaultCenter] 
 addObserver:self
 selector:@selector(userDefaultsDidChange)
 name:NSUserDefaultsDidChangeNotification
 object:nil];

- (void)userDefaultsDidChange {
    [self performSelectorOnMainThread:@selector(updateUIWithNewUserDefaults)
                           withObject:nil
                        waitUntilDone:NO];
}

- (void)updateUIWithNewUserDefaults {
    // Update UI
}

推荐答案

您应该向UI线程的调度队列发送消息并从那里进行UI修改。

You should send a message to the UI thread's dispatch queue and do your UI modifications from there.

喜欢这样：

dispatch_async(dispatch_get_main_queue(), ^{
  // your code here
});

参见 Apple的Grand Central Dispatch文档

--- Dave

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