Enable and Disable Keyboard return key on demand in iOS

问题

I have a UITextField. While user is typing, I am using

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

to validate the string. And if the string is valid I want to enable the return key; if it is not valid I want to disable the return key. Is there a way to do this?

For example the return key would be disabled while the user types the characters in avai. Then the return would become enabled after the user finishes typing avail. Then the return would be disabled again as user types availabl; then become enabled again as user types available.

来源：https://stackoverflow.com/questions/25728778/enable-and-disable-keyboard-return-key-on-demand-in-ios