如何向UITextField和UITextView添加方法？

// UIView+UITextInputTraits.h

@interface UIView (UITextInputTraits)
- (void)changeKeyboardType:(UIKeyboardType)keyboardType;    
@end


// UIView+Additions.m

#import \"UIView+UITextInputTraits.h\"

@implementation UIView (UITextInputTraits)

- (void)changeKeyboardType:(UIKeyboardType)keyboardType {
    if ([self conformsToProtocol:@protocol(UITextInputTraits)]) {
        id<UITextInputTraits> textInput = (id<UITextInputTraits>)self;
        if (textInput.keyboardType != keyboardType) {
            [self resignFirstResponder];
            textInput.keyboardType = keyboardType;
            [self becomeFirstResponder];
        }
    }
}

@end

@interface UITextField (ChangeKeyboard)
- (void)changeKeyboardType:(UIKeyboardType)keyboardType;
@end

@implementation UITextField (ChangeKeyboard)
- (void)changeKeyboardType:(UIKeyboardType)keyboardType {
    self.keyboardType = keyboardType;
    [self resignFirstResponder];
    [self becomeFirstResponder];
}
@end