Why textFieldShouldBeginEditing method cannot be triggered?

I has declared in .h file

@interface TextFieldDemoViewController : UIViewController <UITextFieldDelegate>

and implements this protocol method

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField{
NSLog(@"OK");
return NO;
}

Build and click a textfield, but nothing happen. Did I miss something?

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OK, I has resolved 开发者_运维问答it: Connect textfield's Outlet 'delegate' to File's owner in IB

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Connect textfield's Outlet 'delegate' to File's owner in IB