ios - 在 'tag' 类型的对象上找不到属性 '_strong id'

Question

我正在根据本教程 (http://bit.ly/NI9kQe) 构建一个应用程序，它使用自定义 Web API 连接到 Web 服务器。其中一项要求是检测是否点击了登录或注册按钮。这是使用在界面生成器中为按钮设置的“标签”完成的(注册按钮的标签为 1)。

代码块位于 btnLoginRegisterTapped 方法中，如下所示(错误发生在 -> NSString* command = (sender.tag==1)?@"register":@"login"; 行):

- (IBAction)btnLoginRegisterTapped:(id)sender {

//form fields validation
if (fldUserName.text.length < 4 || fldPassword.text.length < 4) {
  //  [UIAlertView error:@"Enter username and password over 4 chars each."];

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Opps!!" message:@"Enter  username and password over 4 chars each." delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil];
    // optional - add more buttons:
    [alert addButtonWithTitle:@"Yes"];
    [alert show];
    return;

}

//salt the password
NSString* saltedPassword = [NSString stringWithFormat:@"%@%@", fldPassword.text, kSalt];

//prepare the hashed storage
NSString* hashedPassword = nil;
unsigned char hashedPasswordData[CC_SHA1_DIGEST_LENGTH];

//hash the pass
NSData *data = [saltedPassword dataUsingEncoding: NSUTF8StringEncoding];
if (CC_SHA1([data bytes], [data length], hashedPasswordData)) {
    hashedPassword = [[NSString alloc] initWithBytes:hashedPasswordData length:sizeof(hashedPasswordData) encoding:NSASCIIStringEncoding];
} else {

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Opps!!" message:@"Password cannot be reset!" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil];
    // optional - add more buttons:
    [alert addButtonWithTitle:@"Yes"];
    [alert show];
    return;
}

//************ THIS IS WHERE THE ERROR OCCURS *****************//
//check whether it's a login or register 
NSString* command = (sender.tag==1)?@"register":@"login";
NSMutableDictionary* params =[NSMutableDictionary dictionaryWithObjectsAndKeys:
                              command, @"command",
                              fldUserName.text, @"username",
                              hashedPassword, @"password",
                              nil];

//make the call to the web API
[[API sharedInstance] commandWithParams:params
                           onCompletion:^(NSDictionary *json) {
                               //handle the response
                               //result returned
                               NSDictionary* res = [[json objectForKey:@"result"] objectAtIndex:0];

                               if ([json objectForKey:@"error"]==nil && [[res objectForKey:@"IdUser"] intValue]>0) {
                                   //success
                                   [[API sharedInstance] setUser: res];
                                   [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];

                                   //show message to the user
                                   [[[UIAlertView alloc] initWithTitle:@"Logged in"
                                                               message:[NSString stringWithFormat:@"Welcome %@",[res objectForKey:@"username"] ]
                                                              delegate:nil
                                                     cancelButtonTitle:@"Close"
                                                     otherButtonTitles: nil] show];

                               } else {
                                   //error

                                   UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Opps!!" message:@"Server down? Try Again" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil];
                                   // optional - add more buttons:
                                   [alert addButtonWithTitle:@"Yes"];
                                   [alert show];
                                   return;

                               }

                           }];

当我尝试构建项目(实际上是工作区)时出现错误:

在“_strong id”类型的对象上找不到属性“标签”

我正在使用 xcode 5.0 为 iOS7 部署。

谢谢，

Answer 1

属性语法不能与通用 id 类型的变量一起使用。

因此，要么用方法调用 [sender tag] 替换 sender.tag，要么更好，在方法定义中使用 sender 参数的实际类型:

- (IBAction)btnLoginRegisterTapped:(UIButton *)sender { ... }

提示:在 Xcode 中使用“Control-Drag”创建 Action 时，使用“类型”字段中的弹出窗口选择发件人的实际类型。然后使用正确的参数类型创建操作方法。