Question

我将在我的应用程序中显示一种UIActivityIndicatorView，同时在for（）循环中解析几个JSON对象。我无法想象我必须放置[UIActivityIndicatorView startAnimating]和[UIActivityIndicatorView stopAnimating]以显示解析的真实END（在完成for（）循环的末尾）。这是简化的代码：

- (void)parseMethod {

// other stuff

        for (int i=0; i < [arrayJSON count]; i++) {

            NSURL *url = [NSURL URLWithString:
                          [NSString stringWithFormat:
                           @"http://WWW.REMOTESERVERWITHJSONSOURCE.NET/%@",[arrayJSON objectAtIndex:i]]];

            NSURLRequest *request = [NSURLRequest requestWithURL:url];
            AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {

                NSMutableDictionary *arrayMain = [JSON objectForKey:@"main"];
                NSMutableDictionary *arrayMain2 = [JSON objectForKey:@"main2"];
                [arrayA1 addObject:[arrayMain valueForKey:@"A1"]];
                [arrayA2 addObject:[arrayWind valueForKey:@"A2"]];

                // HERE FINISH PARSING AFJSONREQUESTOPERATION
                // IF I PUT HERE [UIActivityIndicatorView stopAnimating] IT SHOWS AT THE END OF FIRST for () LOOP

                [table reloadData];
                [table scrollRectToVisible:CGRectMake(0, 0, 1, 1) animated:YES]
            }
                                                                            failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
                                                                            NSLog(@"%@", [error userInfo]);
                                                                        }];
            [operation start];
            // HERE START PARSING AFJSONREQUESTOPERATION
            [UIActivityIndicatorView startAnimating] 
        }

    // HERE FINISH THE for () LOOP ??
    // IF I PUT HERE [UIActivityIndicatorView stopAnimating] IT SHOWS AGAIN AT THE END OF FIRST for () LOOP

} 

    // HERE FINISH THE parseMethod ??
    // IF I PUT HERE [UIActivityIndicatorView stopAnimating] IT SHOWS AGAIN AT THE END OF FIRST for () LOOP

    }

正如你所看到的，我无法找到放置[UIActivityIndicatorView stopAnimating]的真实位置，'cos它在FIRST解析结束时停止的任何地方（首先用于（）循环）：所以，有一种方法可以等待整个for（）循环在整个循环后调用[UIActivityIndicatorView stopAnimating]（或其他方法）？谢谢！

ALTERNATIVE 也许解析速度太快，我看不到UIActivityIndicatorView出现和加载？在这种情况下，在哪里我必须把一种计时器（或睡眠（unsigned int））等待几秒才消失？

Answer 1

你的问题是你在循环中发出的请求是异步的，所以你的循环不会让它们完成，它只是快速连续触发每个循环，你加载数组的代码块是收到数据后执行。

你可以在你的块中使用一个计数器，每当一个块完成时它会递增，然后一旦计数器与你知道何时停止动画的[arrayJSON count]匹配。请记住使用__block存储

http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/Blocks/Articles/bxVariables.html

Answer 2

解决方案是

简化代码，以便明白在那里做的事情（预先声明块）
计算正在运行的请求数，并仅在完成所有请求后执行全局操作。

typedef void (^AFJSONSuccessBlock) (NSURLRequest *request, NSHTTPURLResponse *response, id JSON);
typedef void (^AFJSONFailureBlock) (NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON);

[UIActivityIndicatorView startAnimating];

__block int numRequests = [arrayJSON count];

AFJSONSuccessBlock onSuccess = ^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {   
    [...]

    numRequests--;

    if (numRequests == 0) {
        [UIActivityIndicatorView stopAnimating];
    }
};

AFJSONFailureBlock onFailure = ^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
    [...]

    numRequests--;

    if (numRequests == 0) {
        [UIActivityIndicatorView stopAnimating];
    }
};

for (NSString* jsonPath in arrayJSON) {
    NSString* absolutePath = [NSString stringWithFormat:@"http://WWW.REMOTESERVERWITHJSONSOURCE.NET/%@", jsonPath];
    NSURL *url = [NSURL URLWithString:absolutePath];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    AFJSONRequestOperation *operation;
    operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request
                                                                success:onSuccess
                                                                failure:onFailure];
    [operation start];
}

Answer 3

我通常会说，如果您无法确定代码中循环的结束位置，则表明您的代码会被复杂化。你的for循环在我认为的else语句之前结束。要找出你可以简单地点击起始括号和XCode（如果那是你正在使用的）将突出显示代码块......

检测objective-c中for（）循环的实际结束

3 个答案: