在iOS中对后台线程执行任务，即使应用程序进入后台也能继续执行：

问题描述

如何在后台线程上执行？即使用户按下主页按钮，执行也应在后台继续。

How to perform execution on a background thread? Execution should continue in the background even if the user presses the home button.

推荐答案

将这些属性添加到.h文件中

Add these properties to your .h file

@property (nonatomic, strong) NSTimer *updateTimer;
@property (nonatomic) UIBackgroundTaskIdentifier backgroundTask;

现在假设您对按钮有一个操作 - > btnStartClicked
那么您的方法将是喜欢：

Now suppose you have a action on button --> btnStartClickedthen your method would be like :

-(IBAction)btnStartClicked:(UIButton *)sender {
    self.updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.5
                                                        target:self
                                                      selector:@selector(calculateNextNumber)
                                                      userInfo:nil
                                                       repeats:YES];
    self.backgroundTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        NSLog(@"Background handler called. Not running background tasks anymore.");
        [[UIApplication sharedApplication] endBackgroundTask:self.backgroundTask];
        self.backgroundTask = UIBackgroundTaskInvalid;
    }];

}

 -(void)calculateNextNumber{
    @autoreleasepool {
      // this will be executed no matter app is in foreground or background
    }
}

如果你需要停止使用这种方法，

and if you need to stop it use this method,

- (IBAction)btnStopClicked:(UIButton *)sender {

    [self.updateTimer invalidate];
    self.updateTimer = nil;
    if (self.backgroundTask != UIBackgroundTaskInvalid)
    {
        [[UIApplication sharedApplication] endBackgroundTask:self.backgroundTask];
        self.backgroundTask = UIBackgroundTaskInvalid;
    }
    i = 0;
}

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