Property 'tag' not found on object of type '_strong id'

Question

I am building an App according to this tutorial (http://bit.ly/NI9kQe) which uses a custom web api to connect to the web server. One of the requirements is to detect whether or not the Login or Register button has been tapped. This is done using a "tag" which has been set for the button in interface builder (the register button has a tag of 1).

The chunk of code sits inside the btnLoginRegisterTapped method as follows (the error occurs on the line -> 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;

                               }

                           }];

}

when I try to build the project (workspace actually) I get the error:

Property 'tag' not found on object of type '_strong id'

I am using xcode 5.0 deploying for iOS7.

Thanks,

Answer 1

Property syntax cannot be used with variables of the generic id type.

So either replace sender.tag by the method call [sender tag] or better, use the actual type of the sender argument in the method definition:

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

Tip: When creating the action with "Control-Drag" in Xcode, use the pop-up in the "Type" field to select the actual type of the sender. Then the action method is created with the correct argument type.