ios - Objective-c:未声明的标识符 applicationDidEnterBackground

Question

我正在尝试使用来自 this example 的代码:

- (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.

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

我是一名 react-native 开发人员，很抱歉，这可能是个愚蠢的问题:)

我怎么知道我应该从哪里导入这个方法？ applicationDidEnterBackground

Docs也不给我答案。

Answer 1

有两种方法:

AppDelegate

你应该在你的 AppDelegate.m 中实现这个方法 你可以通过查看 main.m 文件找到你的应用程序的委托(delegate)，你会得到类似的东西

int main(int argc, char * argv[]) {
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

AppDelegate 是您应用的委托(delegate)类。

NSNotificationCenter

有一个内置的 UIApplicationDidEnterBackgroundNotification 通知，它在 UIApplication.h 中声明，并且 您可以将任何类型的对象作为观察者添加到 NSNotificationCenter。

[[NSNotificationCenter defaultCenter]
     addObserver:{myObserver}
     selector:@selector({myObserverMethod}:) // adding ":" at the end will provide you the sent notification as parameter to your method
     name:UIApplicationDidEnterBackgroundNotification
     object:nil];

现在你需要在你的{myObserver}类中实现{myObserverMethod}:(NSNotification *)notification

// MyObserver.m
- (void)myObserverMethod:(NSNotification *)notification {
    UIApplication *application = notification.object;
    // Now you can call `[application beginBackgroundTask:]` or etc.
    NSLog(@"applicationDidEnterBackground");
}

注意:不要忘记 prior to iOS 9你需要在完成后调用 [[NSNotificationCenter defaultCenter] removeObserver:{myObserver}]!