ios - 为什么加载数据指示器无法正常工作？

Question

在我的代码中，我在UIAlertView上使用UIActivityIndi​​catorView。它工作正常，但我的问题是未在正确的时间显示。我的意思是说，当设备从Web服务获取数据之后，此加载指示符最后出现，并且这不是礼貌的事情，因为我希望它在Web服务发送或接收数据时出现。

我是iOS应用开发的新手，需要帮助。如果还有其他简单的方法可以做到这一点，那么建议我。
我希望我的问题很清楚，我的问题是根据此代码，当我从Web服务获得答复后，正在显示加载指示符，但我想运行此指示符，因为用户将按“更新”按钮，然后应调用Web服务。告诉我我错了。

这是我正在使用的代码

-(IBAction)update:(id)sender
{

    av=[[UIAlertView alloc] initWithTitle:@"Updating Image..." message:@"" delegate:self cancelButtonTitle:nil otherButtonTitles:nil];
    ActInd=[[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
    [ActInd startAnimating];
    [ActInd setFrame:CGRectMake(125, 60, 37, 37)];
    [av addSubview:ActInd];
    [av show];

    {
        NSUserDefaults *defaults=[NSUserDefaults standardUserDefaults];
        int gid=[defaults integerForKey:@"gid"];
        NSString *gameid=[NSString stringWithFormat:@"%i", gid];
        NSLog(@"%@",gameid);
        img=mainImage.image;
        NSData *imgdata=UIImagePNGRepresentation(img);
        NSString *imgstring=[imgdata base64EncodedString];
        NSLog(@"%@",imgstring);
        NSString *escapedString = (NSString *)CFURLCreateStringByAddingPercentEscapes(
                                                                                      NULL,
                                                                                      (CFStringRef)imgstring,
                                                                                      NULL,
                                                                                      CFSTR("!*'();:@&=+$,/?%#[]"),
                                                                                      kCFStringEncodingUTF8);

        NSLog(@"escapedString: %@",escapedString);
        @try
        {
            NSString *post =[[NSString alloc] initWithFormat:@"gid=%@&image=%@",gameid,escapedString];
            NSLog(@"%@",post);

            NSURL *url=[NSURL URLWithString:@"http://mywebspace/updategameimage.php"];

            NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];

            NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];

            NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
            [request setURL:url];
            [request setHTTPMethod:@"POST"];
            [request setValue:postLength forHTTPHeaderField:@"Content-Length"];
            [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
            [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
            [request setHTTPBody:postData];




            NSError *error = [[NSError alloc] init];
            NSHTTPURLResponse *response = nil;
            NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

            NSLog(@"Response code: %d", [response statusCode]);
            if ([response statusCode] >=200 && [response statusCode] <300)                {
                NSString *responseData = [[NSString alloc]initWithData:urlData encoding:NSUTF8StringEncoding];
                NSLog(@"Response ==> %@", responseData);

                SBJsonParser *jsonParser = [SBJsonParser new];
                NSDictionary *jsonData = (NSDictionary *) [jsonParser objectWithString:responseData error:nil];
                NSLog(@"%@",jsonData);
                NSInteger type = [(NSNumber *)[jsonData objectForKey:@"type"] integerValue];
                NSLog(@"%d",type);

                if (type==1) {
                    [self alertStatus:@"You can Keep on Drawing" :@"Sketch Updated"];
                }


            }
        }
        @catch (NSException * e) {

            NSLog(@"Exception: %@", e);
            [self alertStatus:@"Unable to connect with game." :@"Connection Failed!"];
        }
    }
    [av dismissWithClickedButtonIndex:0 animated:YES];
    [av release]; av=nil;

}

Answer 1

您可以使用GCD，Raywenderlich Tutorial

-(IBAction)update:(id)sender
{
    /*
      Setup indicator and show it
    */
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
        /*
          Do network call
        */
        dispatch_async(dispatch_get_main_queue(), ^{
            /*
              Update UI
            */
        });
    });
}