Question

我的应用程序中定期启动了一些NSOperations。即使将应用程序置于后台，它们也应该完成。为此，我使用beginBackgroundTaskWithExpirationHandler方法。

我是否应该在每次启动任务时使用beginBackgroundTaskWithExpirationHandler / endBackgroundTask:，即使应用程序没有进入后台？或者我只是在检测到UIApplicationDidEnterBackgroundNotification时才调用开始/结束方法？

选项1：每次都使用后台任务

/**
 * This method is called regularly from a NSTimer
 */
- (void)processData
{
    __block UIBackgroundTaskIdentifier operationBackgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
        operationBackgroundId = UIBackgroundTaskInvalid;
    }];

    NSOperation *operation = ...
    [self.queue addOperation:operation];

    operation.completionBlock = ^{
        [[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
        operationBackgroundId = UIBackgroundTaskInvalid;
    };
}

选项2：仅在应用程序即将进入后台时使用后台任务

/**
 * This method is called regularly from a NSTimer
 */
- (void)processData
{

    NSOperation *operation =  ...
    [self.queue addOperation:operation];

}


- (void)applicationDidEnterBackground:(NSNotification *)notification
{
    __block UIBackgroundTaskIdentifier operationBackgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithName:@"EnterBackgroundFlushTask" expirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
        operationBackgroundId = UIBackgroundTaskInvalid;
    }];

    // wait for all operations to complete and then


    // let UIApplication know that we are done
    [[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
}

Answer 1

回答我自己的问题。来自Apple Docs：

您无需等到应用移至后台即可指定后台任务。一个更有用的设计是调用 beginBackgroundTaskWithName：expirationHandler：或 beginBackgroundTaskWithExpirationHandler：开始之前的方法任务并在完成后立即调用endBackgroundTask：方法。您你的应用程序在执行时，甚至可以遵循这种模式前景。

其他Apple API reference：

您应该在未完成任务的情况下调用此方法，这可能会损害您应用的用户体验。

您可以在应用执行的任何时候调用此方法。

Answer 2

Option2 是正确的选项。这是Apple文档中的代码供您参考。

 - (void)applicationDidEnterBackground:(UIApplication *)application
{
    bgTask = [application beginBackgroundTaskWithName:@"MyTask" expirationHandler:^{
        // Clean up any unfinished task business by marking where you
        // stopped or ending the task outright.
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];

    // Start the long-running task and return immediately.
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Do the work associated with the task, preferably in chunks.

        [self processData];
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    });
}

Apple developer Guide

我可以使用beginBackgroundTaskWithName进行常规应用处理

2 个答案: