如何在使用*分派时发布NSNotification ?

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:

我发现，正如我在为文件编写映像时预测的那样，我的UI在此期间被阻塞，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，这样我就可以做一些其他与完成相关的工作。初始工作，但UI阻塞代码:

-(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];
}

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:

为了避免UI阻塞，我已经将writeToFile放入了一个*调度队列中，以便它作为一个并发线程运行。但是当写完线程完成后，我想发布一个NSNotification。我不能，因为代码显示在这里，因为它在后台线程中。但这正是我想要实现的功能，意识到这并不是可行的代码:

-(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];
            }
        });
    });
}

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

这里发布此通知以获得我想要的功能的正确机制是什么?

2 个解决方案

#1

A couple possibilities here.

两个可能性。

How about [NSObject performSelectorOnMainThread: ...] ?

那么[NSObject performSelectorOnMainThread]:……]?

E.G.

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];
            }
        });
    });
}

More details at http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorOnMainThread:withObject:waitUntilDone:

更多细节在http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html / / apple_ref / occ / instm / NSObject / performSelectorOnMainThread:withObject:waitUntilDone:

or 2)

或2)

Completion Callbacks

完成回调

as seen at How can I be notified when a dispatch_async task is complete?

如在dispatch_async任务完成时如何通知我?

#2

-(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];
            }
        });
    });
}

That is already correct. However why do you need to use notification if you already dispatch_get_main_queue()?

这已经是正确的。但是，如果已经dispatch_get_main_queue()，为什么需要使用通知呢?

Just use

只使用

        dispatch_async(dispatch_get_main_queue(), ^{
            if (jpgData) {        
            //Do whatever you want with the image here
            }
        });

Anyway your original solution is fine. It's not blocking. Basically it'll save the file at other thread and once it's done it'll do what it takes.

不管怎样，你最初的解决方案是好的。这不是阻碍。基本上，它会将文件保存到其他线程，一旦完成，它就会做它需要做的事情。

What ever you do will be done on the same thread with the thread that call [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:self]; namely main thread.

无论你做什么，都会在调用[[NSNotificationCenter defaultCenter] postNotificationName: kimagesavedsuccessful object:self]的线程的同一线程上完成;也就是主线程。

#1