ios - 在目标 C 中序列化异步任务

我希望能够“真正地”序列化异步方法，例如:

发出网络请求

显示 UIAlertView

这通常是一项棘手的业务，大多数串行队列示例在 NSBlockOperation 的块中显示“ sleep ”。这不起作用，因为只有在回调发生时操作才完成。

我已经通过继承 NSOperation 来实现这一点，这是实现中最有趣的部分:

+ (MYOperation *)operationWithBlock:(CompleteBlock)block
{
    MYOperation *operation = [[MYOperation alloc] init];
    operation.block = block;
    return operation;
}

- (void)start
{
    [self willChangeValueForKey:@"isExecuting"];
    self.executing = YES;
    [self didChangeValueForKey:@"isExecuting"];
    if (self.block) {
        self.block(self);
    }
}

- (void)finish
{
    [self willChangeValueForKey:@"isExecuting"];
    [self willChangeValueForKey:@"isFinished"];
    self.executing = NO;
    self.finished = YES;
    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
}

- (BOOL)isFinished
{
    return self.finished;
}

- (BOOL) isExecuting
{
    return self.executing;
}

这很好用，这是一个演示......

NSOperationQueue *q = [[NSOperationQueue alloc] init];
q.maxConcurrentOperationCount = 1;

dispatch_queue_t queue = dispatch_queue_create("1", NULL);
dispatch_queue_t queue2 = dispatch_queue_create("2", NULL);

MYOperation *op = [MYOperation operationWithBlock:^(MYOperation *o) {
    NSLog(@"1...");
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"1");
        [o finish]; // this signals we're done
    });
}];

MYOperation *op2 = [MYOperation operationWithBlock:^(MYOperation *o) {
    NSLog(@"2...");
    dispatch_async(queue2, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"2");
        [o finish]; // this signals we're done
    });
}];

[q addOperations:@[op, op2] waitUntilFinished:YES];

[NSThread sleepForTimeInterval:5];

请注意，我还使用了 sleep ，但确保它们在后台线程中执行以模拟网络调用。日志内容如下

1...
1
2...
2

这是所需要的。这种方法有什么问题？有什么我应该注意的警告吗？

最佳答案

乍一看这行得通，但有些部分缺少“适当的” NSOperation 子类。

您不应对“取消”状态，您应该在开始时检查 isCancelled，如果返回 YES ( "responding to the cancel command" )，则不要开始
isConcurrent 方法也需要被覆盖，但为了简洁起见，您可能省略了它。