iOS UITextField限制字数

    NSInteger length = 15;
    
    NSString *toBeString = textfield.text;
    NSString *lang = [[UIApplication sharedApplication]textInputMode].primaryLanguage; // 键盘输入模
    if ([lang isEqualToString:@"zh-Hans"]) { // 简体中文输入，包括简体拼音，健体五笔，简体手写
        UITextRange *selectedRange = [textfield markedTextRange];
        //获取高亮部分
        UITextPosition *position = [textfield positionFromPosition:selectedRange.start offset:0];
        // 没有高亮选择的字，则对已输入的文字进行字数统计和限制
        if (!position) {
            if (toBeString.length > length){
                NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:length];
                if (rangeIndex.length == 1){
                    textfield.text = [toBeString substringToIndex:length];
                }
                else{
                    NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, length)];
                    textfield.text = [toBeString substringWithRange:rangeRange];
                }
            }
        }
    } else{ // 中文输入法以外的直接对其统计限制即可，不考虑其他语种情况
        if (toBeString.length > length){
            NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:length];
            if (rangeIndex.length == 1){
                textfield.text = [toBeString substringToIndex:length];
            }else{
                NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0,length)];
                textfield.text = [toBeString substringWithRange:rangeRange];
            }
        }
    }