ios - 获取 JSON 数据时显示事件指示器

Question

我是 IOS 编程的初学者。我的问题是我的应用程序从我的网络服务器中的 JSON 获取数据，当启动应用程序时，由于获取过程，它会稍微滞后和延迟，所以我想在连接到 JSON 数据时显示事件指示器。我该怎么做？

我的 JSON 编码:

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSURL *urlAddress = [NSURL URLWithString:@"http://emercallsys.webege.com/RedBoxApp/getEvents.php"]; 
    NSStringEncoding *encoding = NULL;
    NSError *error;

    NSString *jsonreturn = [[NSString alloc] initWithContentsOfURL:urlAddress usedEncoding:encoding error:&error];
    NSData *jsonData = [jsonreturn dataUsingEncoding:NSUTF32BigEndianStringEncoding];

    NSDictionary * dict = [[CJSONDeserializer deserializer] deserializeAsDictionary:jsonData error:&error];
    if (dict)
    {
        eventsDetail = [[dict objectForKey:@"eventsDetail"] retain];
    }

    [jsonreturn release];
}

Answer 1

使用下面的代码

//add a UIActivityIndicatorView to your nib file and add an outlet to it
[indicator startAnimating];
indicator.hidesWhenStopped = YES;

dispatch_queue_t queue = dispatch_get_global_queue(
                                                   DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
    //Load the json on another thread
    NSString *jsonreturn = [[NSString alloc] initWithContentsOfURL:urlAddress usedEncoding:encoding error:NULL];
    [jsonreturn release];        
    //When json is loaded stop the indicator
    [indicator performSelectorOnMainThread:@selector(stopAnimating) withObject:nil waitUntilDone:YES];
});