使用 Grand Central Dispatch 时如何发布 NSNotification?

问题描述

我发现正如我在将图像写入文件时所预测的那样，我的 UI 在此期间被阻止，这是不可接受的.当我将图像写入文件时，我会发布一个 NS 通知，以便我可以做一些与该完成相关的其他特定工作.原始工作但 UI 阻塞代码:

I found that as predicted when I was writing an image to file that my UI was blocked for the duration, which was not acceptable. When I write the image to file I then post an NS Notification so that I can do some other specific jobs related to that completion. Original working but UI blocking code:

-(void)saveImageToFile {
    NSString *imagePath = [self photoFilePath];
    BOOL jpgData = [UIImageJPEGRepresentation([[self captureManager] stillImage], 0.5) writeToFile:imagePath atomically:YES];

if (jpgData) {        
    [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:self];
}

为避免 UI 阻塞，我将 writeToFile: 放入 Grand Central Dispatch 队列中，以便它作为并发线程运行.但是当写入完成并且线程完成时，我想发布一个 NSNotification.我不能，因为这里显示了代码，因为它在后台线程中.但这是我想要完成的功能，意识到这不是可行的代码:

To avoid the UI blocking I have put the writeToFile: into a Grand Central Dispatch queue so it runs as a concurrent thread. But when the write is completed and the thread is done, I want to post an NSNotification. I cannot as the code is shown here because it is in a background thread. But that is the functionality I want to accomplish, realizing this is not workable code:

-(void)saveImageToFile {
    NSString *imagePath = [self photoFilePath];

    // execute save to disk as a background thread
    dispatch_queue_t myQueue = dispatch_queue_create("com.wilddogapps.myqueue", 0);
    dispatch_async(myQueue, ^{
        BOOL jpgData = [UIImageJPEGRepresentation([[self captureManager] stillImage], 0.5) writeToFile:imagePath atomically:YES];
        dispatch_async(dispatch_get_main_queue(), ^{
            if (jpgData) {        
            [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:self];
            }
        });
    });
}

在这里发布此通知以获得我想要的功能的正确机制是什么?

What is the correct mechanism here to post this notification to gain the functionality I want ?

推荐答案

这里有几个可能性.

1)

[NSObject performSelectorOnMainThread: ...] 怎么样?

How about [NSObject performSelectorOnMainThread: ...] ?

例如

-(void) doNotification: (id) thingToPassAlong
{
    [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:thingToPassAlong];
}

-(void)saveImageToFile {
    NSString *imagePath = [self photoFilePath];

    // execute save to disk as a background thread
    dispatch_queue_t myQueue = dispatch_queue_create("com.wilddogapps.myqueue", 0);
    dispatch_async(myQueue, ^{
        BOOL jpgData = [UIImageJPEGRepresentation([[self captureManager] stillImage], 0.5) writeToFile:imagePath atomically:YES];
        dispatch_async(dispatch_get_main_queue(), ^{
            if (jpgData) {   
                [self performSelectorOnMainThread: @selector(doNotification:) withObject: self waitUntilDone: YES];
            }
        });
    });
}

更多详情请访问 http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorOnMainThread:withObject:waitUntilDone:

或 2)

完成回调

如 如何当 dispatch_async 任务完成时我会收到通知?