login - how do i make an IF statement on xcode that makes a UIButton work? -

I want to create an IF / Else statement that will provide the user only when it has the right code input - for example , A log - If John Smith is put in the Username text box, he will press the login button, otherwise, this will not work.

I have the code

  if ([usernameText.text suffix = @zagerate]] {(code which gives the functionality in the "login button" ) And ([Insertion code that does not provide functionality "Login button"])   
 I also want to do this with a password which is made up of points   
 
 
 Try it out:  
  if ([usernameText.text equalitestring: @ "jejert" ]) {YourButton.enabled = YES; } And {yourButton.enabled = NO; }