objective-c - NSOperationQueue 在 ios4 的主线程上执行，而不是在 io5 上执行？

Question

NSOperationQueue 在 ios 4.2.1 的主线程上执行并在 ios 5.0.1 的单独线程(如预期)上运行是否有任何原因。

我正在使用 NSOperationQueue 在启动我的应用程序时对大量图片 (ALassets) 执行繁忙的操作，但它在 ios4 的主线程上运行，而不是在 ios5 上...

这是一段代码

来自主线程:

    cacheManager = [[PicturesCacheManager alloc] initWithDelegate:self];
    //start the generation of the pictures array
    NSLOG(@"setUpToDatePicturesArray");
    operationQueue = [[NSOperationQueue alloc] init];
    [operationQueue addOperation:cacheManager];
    [cacheManager release];

来自图片缓存管理器:

- (id)initWithDelegate:(id <CachePicturesProtocol> )delegatePic
{
    self = [super init];
    if (self) {
        // Initialization code here.
        [self setDelegate:delegatePic];
    }

return self;
} 

-(void)main{
    [self loadCurrentCameraRoll]; //do lot of stuff 
}

-(void)loadCurrentCameraRoll{
//NSLOG(@"loadCurrentCameraRoll");
// photos
void (^assetEnumerator)( ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop) {
    //photos only!
    if(result != NULL && [[result valueForProperty:@"ALAssetPropertyType"] isEqualToString:@"ALAssetTypePhoto"]) {

        //Do stuff
    }
};

void (^assetGroupEnumerator)( ALAssetsGroup *, BOOL *) =  ^(ALAssetsGroup *group, BOOL *stop) {
    if(group != nil) {
        NSLOG(@"current group = %@", group);
        [group enumerateAssetsUsingBlock:assetEnumerator];
    }
    else{
        //we've enumerated all the groups

    }
};

assetsList = [[NSMutableArray alloc] init];
ALAssetsLibrary *library = [[[ALAssetsLibrary alloc] init] autorelease];

[library enumerateGroupsWithTypes:ALAssetsGroupAll
                       usingBlock:assetGroupEnumerator
                     failureBlock: ^(NSError *error) {
                         NSLOG(@"Failure : %@", [error description]);
                     }];

}

更新:这件事似乎来自 enumerateGroupsWithTypes:usingBlock:failureBlock: 方法。在我调用它之前，我实际上在一个单独的线程中，但在它通过后切换到主线程......

Answer 1

来自 here :

In iOS, operation queues do not use Grand Central Dispatch to execute operations. They create separate threads for non-concurrent operations and launch concurrent operations from the current thread. For a discussion of the difference between concurrent and non-concurrent operations and how they are executed, see NSOperation Class Reference.

因此，NSOperationQueue 总是在单独的线程上执行