ios - Disabling Custom Keyboards for Specific Text Fields -

i trying disable user using own keyboards in 1 of text fields. when doing research, found out needed following code disable custom keyboards:

func application(application: uiapplication, shouldallowextensionpointidentifier extensionpointidentifier: string) -> bool {     if extensionpointidentifier == uiapplicationkeyboardextensionpointidentifier {         return false     }     return true } 

however, not disable keyboards of text fields. how can apply text field only? thanks!