textFieldDidBeginEditing：用于多个文本字段

-(void)textFieldDidBeginEditing:(UITextField *)textField {     
    if (textField.tag == 2) {
        //this is textfield 2, so call your method here
    }
}

-(void)textFieldDidBeginEditing:(UITextField *)textField {     
    NSLog(@\"The method was called\");
}

func textFieldDidBeginEditing(textField: UITextField) {
    if textField.tag == 2 {
        //this is textfield 2, so call your method here
    }
}

   -(void)textFieldDidBeginEditing: (UITextField *)textField
   {     
        if (textField == mySecondTextField)
        {
            //Do what you need
        }
        else
        {
            //Do nothing
        }
   }

#define kUsernameField 100
#define kPasswordField 101
#define kStartButton 300

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    switch (textField.tag) {
        case kUsernameField:
            // do user name stuff
            break;

        case kPasswordField:
            // do password stuff
            break;

        default:
            NSLog(@\"No case statement for %@\", [textField description]);
            break;
    }    
}

- (IBAction)buttonTouchUp:(id)sender {
    UIButton *button = (UIButton *)sender;

    // don\'t like
    if ([button.currentTitle isEqualToString:@\"Start\"] == NSOrderedSame) {
        // because if localize your for other language then you will have
        // include code for those other language
        //     French: Démarrer
        //     Spanish: Inicio
        // blah blah blah
    }

    // better
    if (button.tag == kStartButton) {
        // very simple, no code changes for localization
        // blah blah blah
    }

}

button.tag = kStartButton;
// or
[button setTag:kStartButton];

.h

UITextFieldDelegate

myInput.delegate = self;

-(void)textFieldDidBeginEditing:(UITextField *)sender
{
    if ([sender isEqual:myInput])
    {
        NSLog(@\"test\");

    }
}