ios - 如何使用事件指示器进行 Web 服务登录

Question

我刚刚创建了一个使用 Web 服务的 iOS 应用程序，我的问题是当我点击登录时， View Controller 处于空闲状态，不显示事件指示器，但是当从 Web 服务获取响应和数据时，下一个 View Controller 是加载;事件指示器很快出现。我希望在点击登录按钮时可以看到事件指示器

---

代码示例:

NSString *username = TextUsername.text; 
NSString *password = Textpassword.text; 
NSString *strLogInUrl=[NSString stringWithFormat:@""]; 
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES]; 
NSLog(@"Url %@",strLogInUrl); 
NSURL *URLGet = [NSURL URLWithString:strLogInUrl]; 
NSData *data = [NSData dataWithContentsOfURL:URLGet]; 
NSError* error; 
DicForAllData = [NSJSONSerialization JSONObjectWithData: data options:kNilOptions error:&error];

Answer 1

正如其他人所指出的，要让 UI 更新，您需要异步执行此操作。在我向您介绍一些细节之前，让我们考虑一下您问题中代码的高级抽象:

[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
NSData *data = [NSData dataWithContentsOfURL:URLGet]; 
// do something with data
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];

您确实想要发出异步请求，而不是同步请求，如下所示:

[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
NSMutableURLRequest *request = ...;
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    // handle the data or connectionError here, inside this block, and remember to turn off activity indicator
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
}];

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问题是，您的代码片段没有正确创建请求。你把这个过程过于简单化了。您的流程确实还应该考虑:

1. 如果您要提供凭据，那通常是 POST 请求，而不是 dataWithContentsOfURL 执行的简单 GET。

2. 您确实应该构造一个正确的 application/x-www-form-urlencoded 请求。

3. 您必须对传递给服务器的数据进行百分比转义(否则，如果密码恰好包含某些保留字符，例如 + 或 &，登录会失败)。

4. 您确实应该处理错误。

将所有这些放在一起，看起来更像是:

// tell the user we're going to do this request for them
// maybe show a `UIActivityIndicatorView`, too

[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

// construct the body of the request; replace the keys `username` and `password` with whatever your web service requires

NSString *username = textUsername.text;
NSString *password = textPassword.text;
NSString *parameterString = [NSString stringWithFormat:@"username=%@&password=%@", [self percentEscapeString:username], [self percentEscapeString:password]];
NSData *httpBody = [parameterString dataUsingEncoding:NSUTF8StringEncoding];

// now create the request itself

NSString *strLogInUrl = @"http://example.com";
NSURL *URLGet = [NSURL URLWithString:strLogInUrl];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URLGet];
[request setHTTPMethod:@"POST"];
[request setHTTPBody:httpBody];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setValue:@"application/json" forHTTPHeaderField:@"Accept"];

// now send the request

[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    if (!data) {
        NSLog(@"connectionError: %@", connectionError);
    } else {
        NSError* error;
        dicForAllData = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

        // do what you want with the data/error here, e.g. `[self.tableView reloadData]` or whatever
    }

    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
}];

并且假设您有一定比例的转义例程，例如:

- (NSString *)percentEscapeString:(NSString *)string
{
    NSString *result = CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
                                                                                 (CFStringRef)string,
                                                                                 (CFStringRef)@" ",
                                                                                 (CFStringRef)@":/?@!$&'()*+,;=",
                                                                                 kCFStringEncodingUTF8));
    return [result stringByReplacingOccurrencesOfString:@" " withString:@"+"];
}

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早些时候，UnicoRahul 询问您是否在使用 AFNetworking。这是值得考虑的，因为它极大地简化了您必须编写的代码:

NSDictionary *params = @{@"username": username, @"password": password};
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];

[manager POST:@"http://example.com" parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject) {
    dicForAllData = responseObject;

    // do what you want with the data here, e.g. `[self.tableView reloadData]` or whatever
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"%@", error);
}];