iOS开发 --- 推送 SDK: Main Thread Checker: UI API called on a background thread-优快云博客

本文解决Xcode9升级后，在后台线程调用UIKit等API导致的MainThreadChecker错误。介绍如何确保通知权限请求等操作在主线程执行。

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Xcode 升级到 Xcode 9后，集成时若提示下述错误：

Main Thread Checker: 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。

[_notificationCenter requestAuthorizationWithOptions:UNAuthorizationOptionAlert | UNAuthorizationOptionBadge | UNAuthorizationOptionSound completionHandler:^(BOOL granted, NSError * _Nullable error) {
    if (granted) {
        // granted
        NSLog(@"User authored notification.");
        // 向APNs注册，获取deviceToken
        [application registerForRemoteNotifications];
    } else {
        // not granted
        NSLog(@"User denied notification.");
    }
}];

应修改为：

[_notificationCenter requestAuthorizationWithOptions:UNAuthorizationOptionAlert | UNAuthorizationOptionBadge | UNAuthorizationOptionSound completionHandler:^(BOOL granted, NSError * _Nullable error) {
    if (granted) {
        // granted
        NSLog(@"User authored notification.");
        // 向APNs注册，获取deviceToken
        dispatch_async(dispatch_get_main_queue(), ^{
            [application registerForRemoteNotifications];
        };
    } else {
        // not granted
        NSLog(@"User denied notification.");
    }
}];