iphone - dispatch_async 没有被调用

Question

我在将 JSON 数据存储到单个对象数组中时遇到问题。看起来问题出在处理 JSON 请求的 dispatch_asynch 的执行中。当我在方法之前创建一个断点而不是单步执行应用程序时，它似乎只是通过发送到 dispatch_async 的 block 。

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
    NSError *error = nil;
    NSURL *url = [NSURL URLWithString:@"http://sleepy-dusk-3603.herokuapp.com/companies.json"];
    NSString *json = [NSString stringWithContentsOfURL:url
                                              encoding:NSASCIIStringEncoding
                                                 error:&error];
    NSLog(@"\nJSON: %@ \n Error: %@", json, error);

    if(!error) {
        NSData *jsonData = [json dataUsingEncoding:NSASCIIStringEncoding];
        NSDictionary *jsonDict = [NSJSONSerialization JSONObjectWithData:jsonData
                                                                 options:kNilOptions
                                                                   error:&error];
        NSArray *tempArray = [NSArray arrayWithObjects:@"Call Support Desk", @"Call Genius Bar", nil];

        for (NSString *name in [jsonDict valueForKeyPath:@"name"]) {
            NSString *tempString = [[NSString alloc] initWithString:name];
            Company *company = [[Company alloc] initWithName:tempString available_actions:tempArray];
            [self addCompany:company];

非常感谢大家对这个问题的帮助和支持。

Answer 1

 if(!error) {
...
      }
else
{
    NSLog(@"%@",[error localizedDescription]);
}

记录错误并找出发生了什么

这段代码我试过并且运行良好

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
    NSError *error = nil;
    NSURL *url = [NSURL URLWithString:@"http://sleepy-dusk-3603.herokuapp.com/companies.json"];
    NSString *json = [NSString stringWithContentsOfURL:url
                                              encoding:NSASCIIStringEncoding
                                                 error:&error];
    NSLog(@"\nJSON: %@ \n Error: %@", json, error);

    if(!error) {
        NSData *jsonData = [json dataUsingEncoding:NSASCIIStringEncoding];
        NSDictionary *jsonDict = [NSJSONSerialization JSONObjectWithData:jsonData
                                                                 options:kNilOptions
                                                                   error:&error];
        NSArray *tempArray = [NSArray arrayWithObjects:@"Call Support Desk", @"Call Genius Bar", nil];

        for (NSString *name in [jsonDict valueForKeyPath:@"name"]) {
            NSString *tempString = [[NSString alloc] initWithString:name];
            NSLog(@"%@",tempString);
        }
    }
});

回应

2013-03-05 22:02:44.312 newTrial[4711:12303] 
JSON: [{"created_at":"2013-03-04T00:09:06Z","id":1,"name":"Apple","updated_at":"2013-03-04T00:09:06Z","actions":[{"created_at":"2013-03-04T00:09:07Z","id":1,"name":"Call Support Desk","updated_at":"2013-03-04T00:09:07Z"},{"created_at":"2013-03-04T00:09:07Z","id":2,"name":"Call Genius Bar","updated_at":"2013-03-04T00:09:07Z"}]},{"created_at":"2013-03-04T02:01:49Z","id":2,"name":"Comcast","updated_at":"2013-03-04T02:01:49Z","actions":[{"created_at":"2013-03-04T02:01:49Z","id":3,"name":"Account Services","updated_at":"2013-03-04T02:01:49Z"}]}] 
 Error: (null)
2013-03-05 22:02:51.766 newTrial[4711:12303] Apple

所以我假设问题出在你将值存储到数组的位置。检查它是否已正确初始化问题可能出在这里

Company *company = [[Company alloc] initWithName:tempString available_actions:tempArray];
[self addCompany:company];