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UITextViewで一文字ずつUndo/Redoする方法

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UITextViewには標準でUndo/Redoの機能があります。しかし、その単位が単語となっているため、必ずしも使いやすくありません。これを一文字単位でUndo/Redoする方法を発見しました。
以下のコードを書いて、どこかでsetupHook()を呼びます。するとその後、概ね一文字ずつ逐次Undo/Redoされるようになります。
(追記:日本語のように変換を介するものも逐次Undo/Redoできる方法も発見しました。)

ObjectiveC
#import <objc/runtime.h>

@implementation UITextView (hook)
- (void)myReplaceRange:(UITextRange *)range withText:(NSString *)text
{
    [self.undoManager beginUndoGrouping];
    [self myReplaceRange:range withText:text];
    [self.undoManager endUndoGrouping];
}

- (void)mySetMarkedText:(NSString *)text selectedRange:(NSRange)range
{
    if (0 < text.length) {
        [self.undoManager beginUndoGrouping];
        [self mySetMarkedText:text selectedRange:range];
        [self.undoManager endUndoGrouping];
    }
}

-(void)myInsertText:(NSString *)text
{
    [self.undoManager beginUndoGrouping];
    [self myInsertText:text];
    [self.undoManager endUndoGrouping];
}

-(void)myDeleteBackward
{
    [self.undoManager beginUndoGrouping];
    [self myDeleteBackward];
    [self.undoManager endUndoGrouping];
}
@end

void setupHook()
{
    static BOOL install = NO;
    if (!install) {
        install = YES;
        Class klass = [UITextView class];
        Method orgMethod = class_getInstanceMethod(klass, @selector(replaceRange:withText:));
        Method myMethod = class_getInstanceMethod(klass, @selector(myReplaceRange:withText:));
        method_exchangeImplementations(orgMethod, myMethod);
        orgMethod = class_getInstanceMethod(klass, @selector(setMarkedText:selectedRange:));
        myMethod = class_getInstanceMethod(klass, @selector(mySetMarkedText:selectedRange:));
        method_exchangeImplementations(orgMethod, myMethod);
        orgMethod = class_getInstanceMethod(klass, @selector(insertText:));
        myMethod = class_getInstanceMethod(klass, @selector(myInsertText:));
        method_exchangeImplementations(orgMethod, myMethod);
        orgMethod = class_getInstanceMethod(klass, @selector(deleteBackward));
        myMethod = class_getInstanceMethod(klass, @selector(myDeleteBackward));
        method_exchangeImplementations(orgMethod, myMethod);
}
T_Fuchi
iPhoneアプリ作ります。代表作はArrow Noteです。
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