IOS Get请求（请求服务器）

@interface HMViewController () <NSURLConnectionDataDelegate>
@property (weak, nonatomic) IBOutlet UITextField *usernameField;
@property (weak, nonatomic) IBOutlet UITextField *pwdField;
- (IBAction)login;

/**
 *  用来存放服务器返回的所有数据
 */
@property (nonatomic, strong) NSMutableData *responseData;
@end

@implementation HMViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

}

/**
 *  登录逻辑
 */
- (IBAction)login
{
    // 1.表单验证(输入验证)
    NSString *username = self.usernameField.text;
    if (username.length == ) { // 没有输入用户名
        [MBProgressHUD showError:@"请输入用户名"];
        return;
    }

    NSString *pwd = self.pwdField.text;
    if (pwd.length == ) { // 没有输入密码
        [MBProgressHUD showError:@"请输入密码"];
        return;
    }

    // 弹框
    [MBProgressHUD showMessage:@"正在拼命登录中..."];

    // 2.发送请求给服务器(带上帐号和密码)
    // GET请求:请求行\请求头

    // 2.1.设置请求路径
    NSString *urlStr = [NSString stringWithFormat:@"http://192.168.1.200:8080/MJServer/login?username=%@&pwd=%@", username, pwd];

    // 转码
    urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

    // URL里面不能包含中文
    NSURL *url = [NSURL URLWithString:urlStr];

    // 2.2.创建请求对象
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; // 默认就是GET请求
    request.timeoutInterval = ; // 设置请求超时

    // 2.3.发送请求
    [self sendAsync:request];

    NSLog(@"---------已经发出请求");
}

#pragma mark - NSURLConnectionDataDelegate 代理方法
/**
 *  请求错误(失败)的时候调用(请求超时\断网\没有网, 一般指客户端错误)
 */
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"connection:didFailWithError:");
    [MBProgressHUD hideHUD];

    [MBProgressHUD showError:@"网络繁忙, 请稍后再试"];
}

/**
 *  当接受到服务器的响应(连通了服务器)就会调用
 */
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSLog(@"connection:didReceiveResponse:");

    // 初始化数据
    self.responseData = [NSMutableData data];
}

/**
 *  当接受到服务器的数据就会调用(可能会被调用多次, 每次调用只会传递部分数据)
 */
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSLog(@"connection:didReceiveData:");

    // 拼接(收集)数据
    [self.responseData appendData:data];
}

/**
 *  当服务器的数据接受完毕后就会调用
 */
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"connectionDidFinishLoading:");

    // 隐藏HUD
    [MBProgressHUD hideHUD];

    // 解析服务器返回的数据
    NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:self.responseData options:NSJSONReadingMutableLeaves error:nil];
    NSString *error =  dict[@"error"];
    if (error) { // 登录失败
        [MBProgressHUD showError:error];
    } else { // 登录成功
        NSString *success =  dict[@"success"];
        [MBProgressHUD showSuccess:success];
    }
}

/**
 *  发送异步请求的方式2: start方法, 代理
 */
- (void)sendAsync2:(NSURLRequest *)request
{
    NSURLConnection *conn = [NSURLConnection connectionWithRequest:request delegate:self];
    [conn start]; // 异步执行
}

/**
 *  发送异步请求的方式1: 类方法, block
 */
- (void)sendAsync:(NSURLRequest *)request
{
    NSOperationQueue *queue = [NSOperationQueue mainQueue];
    [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {  // 当请求结束的时候调用 (拿到了服务器的数据, 请求失败)

        // 隐藏HUD (刷新UI界面, 一定要放在主线程, 不能放在子线程)
        [MBProgressHUD hideHUD];

        /**
         解析data :
         {"error":"用户名不存在"}
         {"error":"密码不正确"}
         {"success":"登录成功"}
         */
        if (data) { // 请求成功
            NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];
            NSString *error = dict[@"error"];
            if (error) { // 登录失败
                [MBProgressHUD showError:error];
            } else { // 登录成功
                NSString *success =  dict[@"success"];
                [MBProgressHUD showSuccess:success];
            }
        } else { // 请求失败
            [MBProgressHUD showError:@"网络繁忙, 请稍后再试"];
        }
    }];
}

@end