iOS4 创建后台定时器

发布于 2024-10-01 17:39:27 字数 212 浏览 5 评论 0原文

我（基本上）需要在 iOS 4 上创建一个后台计时器，它允许我在经过特定时间后执行一些代码。我读到您可以使用一些 [NSThread detachNewThreadSelector: 目标： withObject:]; 但这在实践中是如何工作的呢？我怎样才能确保线程也保持在后台。本地通知对我来说不起作用，因为我需要执行代码，而不是通知用户。

帮助将不胜感激！

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人疚 2024-10-08 17:39:27

您还可以使用 Grand Central Dispatch (GCD) 来执行此操作。这样，您可以使用块将代码保存在一个位置，并且如果您需要在完成后台处理后更新 UI，请确保再次调用主线程。这是一个基本示例：

#import <dispatch/dispatch.h>

…

NSTimeInterval delay_in_seconds = 3.0;
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, delay_in_seconds * NSEC_PER_SEC);
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

UIImageView *imageView = tableViewCell.imageView;

// ensure the app stays awake long enough to complete the task when switching apps
UIBackgroundTaskIdentifier taskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:{}];

dispatch_after(delay, queue, ^{
    // perform your background tasks here. It's a block, so variables available in the calling method can be referenced here.        
    UIImage *image = [self drawComplicatedImage];        
    // now dispatch a new block on the main thread, to update our UI
    dispatch_async(dispatch_get_main_queue(), ^{        
      imageView.image = image;
      [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
    });
});

Grand Central Dispatch (GCD) 参考：
http://developer.apple.com/ Library/ios/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html

块参考：
http://developer .apple.com/library/ios/#featuredarticles/Short_Practical_Guide_Blocks/index.html%23//apple_ref/doc/uid/TP40009758

后台任务参考：
http://developer.apple.com/library/ios/DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html#//apple_ref/occ/instm/UIApplication/beginBackgroundTaskWithExpirationHandler：

You can also do this using Grand Central Dispatch (GCD). This way you can use blocks to keep your code in one place, and be sure you're calling the main thread again if you need to update your UI after you've finished background processing. Here's a basic example:

#import <dispatch/dispatch.h>

…

NSTimeInterval delay_in_seconds = 3.0;
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, delay_in_seconds * NSEC_PER_SEC);
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

UIImageView *imageView = tableViewCell.imageView;

// ensure the app stays awake long enough to complete the task when switching apps
UIBackgroundTaskIdentifier taskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:{}];

dispatch_after(delay, queue, ^{
    // perform your background tasks here. It's a block, so variables available in the calling method can be referenced here.        
    UIImage *image = [self drawComplicatedImage];        
    // now dispatch a new block on the main thread, to update our UI
    dispatch_async(dispatch_get_main_queue(), ^{        
      imageView.image = image;
      [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
    });
});

Grand Central Dispatch (GCD) reference:
http://developer.apple.com/library/ios/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html

Blocks reference:
http://developer.apple.com/library/ios/#featuredarticles/Short_Practical_Guide_Blocks/index.html%23//apple_ref/doc/uid/TP40009758

Background Task reference:
http://developer.apple.com/library/ios/DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html#//apple_ref/occ/instm/UIApplication/beginBackgroundTaskWithExpirationHandler:

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