是否可以在设置 -> iCloud -> 文档和数据中拦截 iCloud 打开/关闭？

Question

如果用户在设置 -> iCloud -> 文档和数据下从开启到关闭iCloud支持是否可以拦截?

显然，当他这样做时，应用程序已经退出活动并进入后台。我的目标是 iOS7，我想与UIManagedDocument 保持同步，否则就像拥有两个不同的 UIDocument：一个支持 iCloud，并且在从打开切换到关闭之前创建了所有数据，另一个没有任何数据在里面。如果我在关闭 iCloud 支持时创建数据，然后再打开，我会得到与关闭支持时相同的数据库。

注意：我相信 nelico 的回答是对的。他写道：“如果您的应用程序正在运行并且用户更改通过设置应用程序启用或禁用文档和数据 iCloud 同步，您的应用程序将收到 SIGKILL 信号。”

当用户更改设置时，应用程序已经在后台并接收到 SIGKILL 信号。这是我不理解和不想要的。注册NSUbiquityIdentityDidChangeNotification 并不能解决这个问题。

Answer 1

另一个更简洁的解决方案是侦听NSUbiquityIdentityDidChangeNotification 通知，当您收到该通知时，检查URLForUbiquityContainerIdentifier 如果它为空，他们要么退出，要么关闭“文档和数据”。您还应该跟踪当前的 ubiquity 令牌，以便您不仅可以知道他们是否注销，而且可以知道他们是否更改了 iCloud 帐户。这种情况的发生超出了人们的想象，因为 Apple Geniuses 喜欢在用户设备出现问题时创建一个新的 iCloud 帐户。

例如：

id <NSObject,NSCopying,NSCoding> _currentUbiquityIdentityToken;

...

_currentUbiquityIdentityToken = [[NSFileManager defaultManager] ubiquityIdentityToken];
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector (_iCloudAccountAvailabilityChanged:) name: NSUbiquityIdentityDidChangeNotification object: nil];

...

- (void)_iCloudAccountAvailabilityChanged:(NSNotification*)notif {
    if (![_currentUbiquityIdentityToken isEqual:[[NSFileManager defaultManager] ubiquityIdentityToken]]) {
        // Update the current token and rescan for documents.
        _currentUbiquityIdentityToken = [[NSFileManager defaultManager] ubiquityIdentityToken];
        // Do something about the change here...
    }
}

Answer 2

通常您会将检查放在下面的方法中。这样，只要应用程序处于活动状态（包括首次启动），您就可以在将控制权返回给用户之前检查设置，而无需在后台进行轮询。对于 UIManagedDocument，您可能希望将商店迁移到仅本地副本并删除任何 iCloud 内容或相反，具体取决于用户输入。

顺便说一句，只需在上一个答案中包含检查，以测试全局 iCloud 设置是否已打开或关闭。我不这样做是因为只有在用户设置了应用特定设置时才需要更改应用行为。

/*! The app is about to enter foreground so use this opportunity to check if the user has changed any
    settings.  They may have changed the iCloud account, logged into or out of iCloud, set Documents & Data to off (same effect as
    if they logged out of iCloud) or they may have changed the app specific settings.
    If the settings have been changed then check if iCloud is being turned off and ask the user if they want to save the files locally.
    Otherwise just copy the files to iCloud (don't ask the user again, they've just turned iCloud on, so they obviously mean it!)

 @param application The application
 */
- (void)applicationWillEnterForeground:(UIApplication *)application
{
    //LOG(@"applicationWillEnterForeground called");

    // Check if the settings have changed
    [[NSUserDefaults standardUserDefaults] synchronize];
    NSUserDefaults* userDefaults = [NSUserDefaults standardUserDefaults];
    bool userICloudChoice = [userDefaults boolForKey:_cloudPreferenceKey];

    // Check against the current in memory setting
    if (userICloudChoice  == useICloudStorage) {

        // The setting has not been changed so just ignore
        //LOG(@" iCloud choice has not changed");


    } else {

        // The setting has changed so do something
        //LOG(@" iCloud choice has been changed!!");

        // iCloud has been turned off so ask the user if they want to keep files locally
        if (!userICloudChoice) {
            //LOG(@" Ask user if  they want to keep iCloud files ?");

            if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
                _cloudChangedAlert = [[UIAlertView alloc] initWithTitle:@"You're not using iCloud" message:@"What would you like to do with documents currently on this phone?" delegate:self cancelButtonTitle:@"Keep using iCloud" otherButtonTitles:@"Keep on My iPhone", @"Delete from My iPhone", nil];
            } else {
                _cloudChangedAlert = [[UIAlertView alloc] initWithTitle:@"You're not using iCloud" message:@"What would you like to do with documents currently on this phone?" delegate:self cancelButtonTitle:@"Keep using iCloud" otherButtonTitles:@"Keep on My iPad", @"Delete from My iPad", nil];

            }

            [_cloudChangedAlert show];

        } else {

            // iCloud has been turned on so just copy the files across, don't ask the user again...

            //LOG(@" iCloud turned on so copy any created files across");
            [[CloudManager sharedManager] setIsCloudEnabled:YES];  // This does all the work based on the settings passed to it
            useICloudStorage = YES;

        }
    }

}

哦，如果用户使用另一个 iCloud 帐户登录，还要注册此通知。

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkUserICloudPreferenceAndSetupIfNecessary) name:NSUbiquityIdentityDidChangeNotification object:nil];

Answer 3

无法拦截更改，但您可以通过编程方式检查它们是否启用了 iCloud：

NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *ubiquityContainerURL = [fileManager URLForUbiquityContainerIdentifier:nil];
if (!ubiquityContainerURL) {
    // iCloud is not enabled
}

当您的应用进入后台时，您可以定期轮询它并让您的应用响应任何状态变化。

编辑：如果您的应用正在运行并且用户通过设置应用更改启用或禁用文档和数据 iCloud 同步，您的应用将收到 SIGKILL 信号。但是，操作系统可能会出于多种原因终止您的应用程序，因此捕获 SIGKILL 不是拦截 iCloud 同步设置更改的可靠方法。你最好还是定期轮询。