代码块位于btnLoginRegisterTapped方法内部,如下所示(错误发生在行 – > NSString * command =(sender.tag == 1)？@“register”：@“login”;)：

- (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(实际工作空间)时,我收到错误：

在’_strong id’类型的对象上找不到属性’tag’

我正在使用xcode 5.0部署iOS7.

谢谢,