iphone - 当用户退出应用程序时保存核心数据？

Question

我正在尝试在用户按下主页按钮时保存核心数据。我想从 -applicationDidEnterBackground: 执行此操作，但它没有被调用。这可能是因为您无法从此处保存核心数据，或者只是因为没有足够的时间来完成操作。但是，它确实可以从 -applicationWillResignActive: 开始工作，我只是好奇在其中执行此操作的最佳委托(delegate)方法是什么，以及为什么 -applicationDidEnterBackground: 不起作用。(正如您从输出中看到的，这两种方法都被调用了，如果我从 -applicationWillResignActive: 中删除保存，则什么也不会发生，所以这不是一个阻塞另一个的情况)

// CALLS SAVE
- (void)applicationWillResignActive:(UIApplication *)application {
    [[self model] saveCoreData:@"SAVE FROM: applicationWillResignActive"];
    NSLog(@"APPDEL: %s", __PRETTY_FUNCTION__);
}

// DOES NOT CALL SAVE
- (void)applicationDidEnterBackground:(UIApplication *)application {
    [[self model] saveCoreData:@"SAVE FROM: applicationDidEnterBackground"];
    NSLog(@"APPDEL: %s", __PRETTY_FUNCTION__);
}

.

// CONSOLE OUTPUT
2013-03-21 cvb[6724:907] APPDEL: -[AppDelegate applicationWillResignActive:]
2013-03-21 cvb[6724:907] APPDEL: -[AppDelegate applicationDidEnterBackground:]
2013-03-21 cvb[6724:907]  
2013-03-21 cvb[6724:907] SAVE: SAVE FROM: applicationWillResignActive
2013-03-21 cvb[6724:907] SAVE: Saving successful ...

编辑:

这就是我最后所做的:

- (void)applicationDidEnterBackground:(UIApplication *)application {
    __block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler:^{
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];
    [[self model] saveCoreData:@"[ENTERING BACKGROUND]"];
}

Answer 1

查看 UIApplicationDelegate protocol reference .

基本上，这是您可能对 applicationDidEnterBackground:

感兴趣的部分

You should perform any tasks relating to adjusting your user interface before this method exits but other tasks (such as saving state) should be moved to a concurrent dispatch queue or secondary thread as needed. Because it's likely any background tasks you start in applicationDidEnterBackground: will not run until after that method exits, you should request additional background execution time before starting those tasks. In other words, first call beginBackgroundTaskWithExpirationHandler: and then run the task on a dispatch queue or secondary thread.