11

我已经子化了一个 NSOperation 并设置了我的 completionBlock，但即使操作完成，它似乎也永远不会进入。这是我的代码：

目录控制器类设置 NSOperation：

- (void)setupOperation {
...

    ImportWordOperation *importWordOperation = [[ImportWordOperation alloc] initWithCatalog:words];
    [importWordOperation setMainObjectContext:[app managedObjectContext]];
    [importWordOperation setCompletionBlock:^{
        [(ViewController *)[[app window] rootViewController] fetchResults];
    }];
    [[NSOperationQueue mainQueue] addOperation:importWordOperation];
    [importWordOperation release];
...
}

如您所见，我正在设置完成块以在其他控制器中的主线程上执行一个方法。

然后，在main我的子类 NSOperation class:ImportWordOperation.m中，我启动了后台操作。isFinished为了触发完成方法，我什至覆盖了 iVar：

- (void)setFinished:(BOOL)_finished {
    finished = _finished;
}

- (BOOL)isFinished {
    return (self.isCancelled ? YES: finished);
}

- (void)addWords:(NSDictionary *)userInfo {
    NSError *error = nil;

    AppDelegate *app = [AppDelegate sharedInstance];

    NSManagedObjectContext *localMOC = [userInfo valueForKey:@"localMOC"];
    NSEntityDescription *ent = [NSEntityDescription entityForName:@"Word" inManagedObjectContext:localMOC];
    for (NSDictionary *dictWord in [userInfo objectForKey:@"words"]) {
        Word *wordN = [[Word alloc] initWithEntity:ent insertIntoManagedObjectContext:localMOC];

        [wordN setValuesForKeysWithDictionary:dictWord];
        [wordN release];
    }

    if (![[userInfo valueForKey:@"localMOC"] save:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    [localMOC reset];

    [self setFinished:YES];
}


- (void)main {

    finished = NO;

    NSManagedObjectContext *localMOC = nil;
    NSUInteger type = NSConfinementConcurrencyType;
    localMOC = [[NSManagedObjectContext alloc] initWithConcurrencyType:type];
    [localMOC setUndoManager:nil];
    [localMOC setParentContext:[self mainObjectContext]];

    if (![self isCancelled]) {
        if ([self.words count] > 0) {
            [self performSelectorInBackground:@selector(addWords:) withObject:@{@"words":self.words, @"localMOC":localMOC}];
        }
    }
}

如果我删除 isFinished 访问器方法，那么完成块会在ImportWordOperation完成之前被调用。

我已经阅读了我发现使用自己的完成块的代码，但是 NSOperation 子类中的完成块有什么用呢？

任何想法或指向类似的已解决情况将不胜感激。

4

2 回答 2

19

您在这里陷入了并发子类和非并发NSOperation子类之间的奇怪空间。通常，当您实施 时main，您的操作是非并发的，并且一旦退出就会isFinished更改为。YESmain

但是，您已经提供了自己的 实现isFinished，并且还对其进行了编码，以便在退出之后isFinished才返回。这使您的操作在许多方面开始像并发操作一样 - 至少包括需要手动发出 KVO 通知。YESmain

您的问题的快速解决方案是setFinished:使用(will|did)ChangeValueForKey:调用来实现。（我还更改了 ivar 名称以反映流行的命名约定）。下面是一个NSOperation子类，我相信它可以准确地模拟您的操作工作，以并发方式完成。

@implementation TestOperation {
    BOOL _isFinished;
}

- (void)setFinished:(BOOL)isFinished
{
    [self willChangeValueForKey:@"isFinished"];
    // Instance variable has the underscore prefix rather than the local
    _isFinished = isFinished;
    [self didChangeValueForKey:@"isFinished"];
}

- (BOOL)isFinished
{
    return ([self isCancelled] ? YES : _isFinished);
}

- (void)main
{
    NSLog(@"%@ is in main.",self);
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        sleep(1);
        [self setFinished:YES];
    });
}

@end

我不熟悉您的要求，所以也许您有迫切的需求，但您的操作似乎更适合使用start而不是main. 我已经实现了一个似乎工作正常的小例子。

@implementation TestOperation {
    BOOL _isFinished;
    BOOL _isExecuting;
}

- (void)setFinished:(BOOL)isFinished
{
    if (isFinished != _isFinished) {
        [self willChangeValueForKey:@"isFinished"];
        // Instance variable has the underscore prefix rather than the local
        _isFinished = isFinished;
        [self didChangeValueForKey:@"isFinished"];
    }
}

- (BOOL)isFinished
{
    return _isFinished || [self isCancelled];
}

- (void)cancel
{
    [super cancel];
    if ([self isExecuting]) {
        [self setExecuting:NO];
        [self setFinished:YES];
    }
}

- (void)setExecuting:(BOOL)isExecuting {
    if (isExecuting != _isExecuting) {
        [self willChangeValueForKey:@"isExecuting"];
        _isExecuting = isExecuting;
        [self didChangeValueForKey:@"isExecuting"];
    }
}

- (BOOL)isExecuting
{
    return _isExecuting;
}

- (void)start
{
    NSLog(@"%@ is in start. isCancelled = %@", self, [self isCancelled] ? @"YES" : @"NO");
    if (![self isCancelled]) {
        [self setFinished:NO];
        [self setExecuting:YES];
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
            sleep(1);
            [self setExecuting:NO];
            [self setFinished:YES];
        });
    }
}
@end
于 2013-03-26T06:30:12.800 回答
1

我在实现NSOperation.

引用关键路径的 Swift 方法是使用#keyPath指令，所以我这样做（_executing并且_finished是我的内部变量）：

self.willChangeValue(forKey: #keyPath(Operation.isExecuting))
self._executing = false
self.didChangeValue(forKey: #keyPath(Operation.isExecuting))

self.willChangeValue(forKey: #keyPath(Operation.isFinished))
self._finished = true
self.didChangeValue(forKey: #keyPath(Operation.isFinished))

不幸的是，#keyPath上面的表达式分别解析为"executing"和"finished"，我们需要为"isExecuting"和抛出 KVO 通知"isFinished"。这就是为什么completionBlock没有被调用的原因。

解决方案是将它们硬编码为：

self.willChangeValue(forKey: "isExecuting")
self._executing = false
self.didChangeValue(forKey: "isExecuting")

self.willChangeValue(forKey: "isFinished")
self._finished = true
self.didChangeValue(forKey: "isFinished")
于 2017-06-21T07:12:55.077 回答