移动推送 iOS SDK: Main Thread Checker: UI API called on a background thread
Xcode 升级到 Xcode 9后，集成时若提示下述错误：
- [backcolor=transparent]Main[backcolor=transparent] [backcolor=transparent]Thread[backcolor=transparent] [backcolor=transparent]Checker[backcolor=transparent]:[backcolor=transparent] UI API called on a background thread
请检查工程中，是否在后台线程（非主线程）调用 AppKit、UIKit相关的API，比如iOS 10+ 请求通知权限时，[application registerForRemoteNotifications];在回调非主线程中执行，则Xcode 9会报上述错误。
- [backcolor=transparent][[backcolor=transparent]_notificationCenter requestAuthorizationWithOptions[backcolor=transparent]:[backcolor=transparent]UNAuthorizationOptionAlert[backcolor=transparent] [backcolor=transparent]|[backcolor=transparent] [backcolor=transparent]UNAuthorizationOptionBadge[backcolor=transparent] [backcolor=transparent]|[backcolor=transparent] [backcolor=transparent]UNAuthorizationOptionSound[backcolor=transparent] completionHandler[backcolor=transparent]:^([backcolor=transparent]BOOL granted[backcolor=transparent],[backcolor=transparent] [backcolor=transparent]NSError[backcolor=transparent] [backcolor=transparent]*[backcolor=transparent] [backcolor=transparent]_Nullable[backcolor=transparent] error[backcolor=transparent])[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]if[backcolor=transparent] [backcolor=transparent]([backcolor=transparent]granted[backcolor=transparent])[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]// granted
- [backcolor=transparent] [backcolor=transparent]NSLog[backcolor=transparent](@[backcolor=transparent]"User authored notification."[backcolor=transparent]);
- [backcolor=transparent] [backcolor=transparent]// 向APNs注册，获取deviceToken
- [backcolor=transparent] [backcolor=transparent][[backcolor=transparent]application registerForRemoteNotifications[backcolor=transparent]];
- [backcolor=transparent] [backcolor=transparent]}[backcolor=transparent] [backcolor=transparent]else[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]// not granted
- [backcolor=transparent] [backcolor=transparent]NSLog[backcolor=transparent](@[backcolor=transparent]"User denied notification."[backcolor=transparent]);
- [backcolor=transparent] [backcolor=transparent]}
- [backcolor=transparent]}];
应修改为：
- [backcolor=transparent][[backcolor=transparent]_notificationCenter requestAuthorizationWithOptions[backcolor=transparent]:[backcolor=transparent]UNAuthorizationOptionAlert[backcolor=transparent] [backcolor=transparent]|[backcolor=transparent] [backcolor=transparent]UNAuthorizationOptionBadge[backcolor=transparent] [backcolor=transparent]|[backcolor=transparent] [backcolor=transparent]UNAuthorizationOptionSound[backcolor=transparent] completionHandler[backcolor=transparent]:^([backcolor=transparent]BOOL granted[backcolor=transparent],[backcolor=transparent] [backcolor=transparent]NSError[backcolor=transparent] [backcolor=transparent]*[backcolor=transparent] [backcolor=transparent]_Nullable[backcolor=transparent] error[backcolor=transparent])[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]if[backcolor=transparent] [backcolor=transparent]([backcolor=transparent]granted[backcolor=transparent])[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]// granted
- [backcolor=transparent] [backcolor=transparent]NSLog[backcolor=transparent](@[backcolor=transparent]"User authored notification."[backcolor=transparent]);
- [backcolor=transparent] [backcolor=transparent]// 向APNs注册，获取deviceToken
- [backcolor=transparent] dispatch_async[backcolor=transparent]([backcolor=transparent]dispatch_get_main_queue[backcolor=transparent](),[backcolor=transparent] [backcolor=transparent]^{
- [backcolor=transparent] [backcolor=transparent][[backcolor=transparent]application registerForRemoteNotifications[backcolor=transparent]];
- [backcolor=transparent] [backcolor=transparent]};
- [backcolor=transparent] [backcolor=transparent]}[backcolor=transparent] [backcolor=transparent]else[backcolor=transparent] [backcolor=transparent]{
- [backcolor=transparent] [backcolor=transparent]// not granted
- [backcolor=transparent] [backcolor=transparent]NSLog[backcolor=transparent](@[backcolor=transparent]"User denied notification."[backcolor=transparent]);
- [backcolor=transparent] [backcolor=transparent]}
- [backcolor=transparent]}];
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阿里云 AI 助理回答
您遇到的问题是由于在非主线程（后台线程）调用了UI相关的API，这在Xcode 9及之后的版本中会触发警告或错误。根据您的描述和代码示例，问题在于registerForRemoteNotifications方法被直接在回调中执行，而这个回调可能不在主线程上运行。
您已经正确地展示了如何修正这个问题：通过使用dispatch_async函数将注册远程通知的操作切换到主线程执行。这样做可以确保所有与UI相关的操作都在主线程上进行，避免了Xcode的警告或错误提示。下面是修正后的代码段：
_notificationCenter requestAuthorizationWithOptions:(UNAuthorizationOptionAlert | UNAuthorizationOptionBadge | UNAuthorizationOptionSound) completionHandler:^(BOOL granted, NSError * _Nullable error) {
if (granted) {
NSLog(@"User authorized notification.");
// 确保在主线程上执行注册操作
dispatch_async(dispatch_get_main_queue(), ^{
[[UIApplication sharedApplication] registerForRemoteNotifications];
});
} else {
NSLog(@"User denied notification.");
}
}];
这段代码中，dispatch_get_main_queue()获取到了主线程的队列，然后通过dispatch_async异步地在这个队列上执行了注册远程通知的操作，从而符合了iOS开发的最佳实践，即只在主线程上处理UI更新和UI相关的API调用。
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