当UITextField成为FirstResponder时得到通知

Question

How I can get notified when UITextField becomeFirstResponder ?

I can check like isFirstResponder or set to to become first Responder by becomeFirstResponder

I want to get notified or handle an event when a user make this text field first responder.

Thanks.

Answer 1

您将需要成为文本字段的委托并实现此可选委托方法：

- (void)textFieldDidBeginEditing:(UITextField *)textField; 

Answer 2

Besides implementing the UITextFieldDelegate method textFieldDidBeginEditing: , you can register for the UITextFieldTextDidBeginEditingNotification notification.

The notification method could be:

- (void)someTextFieldDidBeginEditing:(NSNotification *)notification {
    UITextField *textField = (UITextField *)notification.object;
}

Answer 3

The delegate is definitely the way to go. Unfortunately, in my situation I couldn't use that, because the controller was the delegate of my UITextField subclass and I needed to modify it's placeholder text. Instead I override the methods - (BOOL)canBecomeFirstResponder; & - (BOOL)resignFirstResponder; . Be sure to call super.

Answer 4

For OSX you should be aware of buttons having side effects when relying on the NSControlTextDidBeginEditingNotification .

When you start editing, push some buttons, and resume editing the text field, you won't get a second NSControlTextDidBeginEditingNotification when you resume editing.

In case this behavior causes a problem, UITextFieldTextDidChangeNotification might be an alternative.