iOS UITextField限制输入长度，处理中文输入法下的缺

在很多情况下都会要求限制输入框的字数长度，在非中文情况下简单的处理下即可，但在系统自带的中文输入发现你会发现，即使输入拼音也会被限制。我们需要对中文输入法进行单独的设置：
1.给UITextField绑定一个方法：
[_summaryField addTarget:self action:@selector(editChange:) forControlEvents:UIControlEventEditingChanged];
2.实现方法
//最多输入6个字

#define kMaxLength 6

 - (void)editChange:(UITextField*)textfield {
       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 > kMaxLength)
                  {
                    NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:kMaxLength];
                    if (rangeIndex.length == 1)
                    {
                        textfield.text = [toBeString substringToIndex:kMaxLength];
                    }
                    else
                    {
                        NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, kMaxLength)];
                        textfield.text = [toBeString substringWithRange:rangeRange];
                    }
                }
            }
        }
// 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
        else{
               if (toBeString.length > kMaxLength)
                {
                    NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:kMaxLength];
                    if (rangeIndex.length == 1)
                    {
                        textfield.text = [toBeString substringToIndex:kMaxLength];
                    }
                    else
                    {
                        NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0,kMaxLength)];
                        textfield.text = [toBeString substringWithRange:rangeRange];
                    }
                }
}```