How to add a method to UITextField & UITextView?

I want to put something like this in a method for开发者_运维技巧 UITextField & UITextView.

- (void)changeKeyboardType:(UIKeyboardType)keyboardType {
    paymentTextView.keyboardType = UIKeyboardTypeAlphabet;
    [paymentTextView resignFirstResponder];
    [paymentTextView becomeFirstResponder];
}

How do I do this? I know I can create categories for both UITextField & UITextView but is it possible to do it in one shot?

By one shot, I mean add it to both classes with one protocol instead of making two categories, one for UITextView & one for UITextField. I've heard a protocol is similar to a Ruby module, but in a Ruby module, I can implement the method. In a protocol, it only seems that I can declare the method but not implement it. Can I also implement the method in the protocol, and then include this protocol in UITextField & UITextView?

How to add a method to an existing protocol in Cocoa? is close but not quite.

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What about something like this?

// 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

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For each of these, you can create a category.

Interface file:

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

Implementation file:

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

That would be the way to add these, but I haven't tested the functionality.

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Like @Josh said, method swizzling isn't what you are looking for. However what I actually had in mind (My bad for not researching more into it before submitting an answer) is to add method at runtime on UITextView and UITextField. While this needs a bit more code to implement, it can give you the sort of one-shot you are looking for (You create a method and add it to both UITextView & UITextField at run-time)

Here's a blog post about it:

http://theocacao.com/document.page/327

http://www.mikeash.com/pyblog/friday-qa-2010-11-6-creating-classes-at-runtime-in-objective-c.html