ios - 每次请求完成后执行 NSURLConnection sendAsynchronousRequest "in order"的次数

Question

如何按顺序执行多个NSURLConnection sendAsynchronousRequest？

我必须执行各种异步请求并获得最终完成。

我想按特定顺序执行这些操作。 让我们说

sendAsynchronousRequest2 应该在 sendAsynchronousRequest1 完成后启动，依此类推...

ɲeuroburɳ这个问题的回答很有用。但是，它并没有解决我的问题

Waiting until two async blocks are executed before starting another block

帮助将不胜感激

Answer 1

我以前做过类似的事情。我使用了一个自定义对象，它包含一个 NSURLRequest 实例和一个 NSURLConnection 样式的 completionHandler。这些对象已创建并添加到队列中。
辅助方法使请求出列并发送。在 NSURLConnection 的原始 completionHandler 中我调用了自定义对象的 completionHandler，然后我再次调用了 helper 方法。这将使下一个请求出列。

在看起来像这样的代码中:

@interface URLRequest: NSObject
@property (strong, nonatomic) NSURLRequest *request;
@property (copy, nonatomic) void (^completionHandler)(NSURLResponse *response, NSData *data, NSError *connectionError);
@end

@implementation URLRequest
@end

// viewController Interface
@property (strong) NSMutableArray *requestsQueue;

// implementation
- (BOOL)sendURLRequest {
    if ([self.requestsQueue count] > 0) {
        URLRequest *request = self.requestsQueue[0];
        [NSURLConnection sendAsynchronousRequest:request.request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
            NSLog(@"Request to url %@ done", response.URL);

            if (request.completionHandler) {
                request.completionHandler(response, data, connectionError);
            }
            [self.requestsQueue removeObjectAtIndex:0];

            if (![self sendURLRequest]) {
                NSLog(@"Queue Completed");
            }
        }];
        return YES;
    }
    else {
        NSLog(@"All requests send");
        return NO;
    }
}

- (void)addRequestToQueue:(URLRequest *)request {
    if (!self.requestsQueue) {
        self.requestsQueue = [NSMutableArray array];
    }
    BOOL queueWasEmpty = [self.requestsQueue count] == 0;
    [self.requestsQueue addObject:request];

    if (queueWasEmpty) {
        NSLog(@"Start request queue");
        [self sendURLRequest];
    }
}

URLRequest *request = [[URLRequest alloc] init];
request.request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.google.com"]];
request.completionHandler = ^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    NSLog(@"Request to www.google.com completed with status %ld", (long)((NSHTTPURLResponse *)response).statusCode);
};
[self addRequestToQueue:request];

request = [[URLRequest alloc] init];
request.request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.stackoverflow.com"]];
request.completionHandler = ^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    NSLog(@"Request to www.stackoverflow.com completed with status %ld", (long)((NSHTTPURLResponse *)response).statusCode);
};
[self addRequestToQueue:request];

这是天真的版本。您必须考虑自己处理错误(和超时)。