iOS Emoji表情输入长度判断，及被截取导致的显示异常的处理

- (void)textFieldEditChanged:(UITextField *)textField
{
    NSString *lang = [[UIApplication sharedApplication] textInputMode].primaryLanguage;// 键盘输入模式
    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) {
            [self handleTextFieldCharLength:textField];
        }
    }
    // 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{
        [self handleTextFieldCharLength:textField];
    }
}

1.保证emoji输入小于要求的长度

/**
 处理textField文本的长度
 */
- (void)handleTextFieldCharLength:(UITextField *)textField
{
    NSString *toBeString = textField.text;
    NSString *str =[toBeString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    if (str.length > WordsNumber) {
        __block NSRange subrange;
        [textField.text enumerateSubstringsInRange:NSMakeRange(0, toBeString.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString * _Nullable substring, NSRange substringRange, NSRange enclosingRange, BOOL * _Nonnull stop)
        {
            subrange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, str.length-substringRange.length)];
        }];
        NSString * result = [toBeString substringWithRange:subrange];
        textField.text = result;
    }
}

2.按照一个emoji长度为1，显示输入的文字字数。

/**
 处理textField文本的长度
 */
- (void)handleTextFieldCharLength:(UITextField *)textField
{
    NSString *str = textField.text;
    NSUInteger charTotal = [self countCharacterLength:str];
    if (charTotal > WordsNumber) {
        NSMutableArray *characters = [NSMutableArray array];
        [textField.text enumerateSubstringsInRange:NSMakeRange(0, str.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString * _Nullable substring, NSRange substringRange, NSRange enclosingRange, BOOL * _Nonnull stop) {
            if (characters.count < WordsNumber) {
                [characters addObject:substring];
            }
            else{
                *stop = true;
            }
        }];
        NSString *resultStr = [characters componentsJoinedByString:@""];
        NSUInteger subCharTotal = [self countCharacterLength:resultStr];
        textField.text = resultStr;
        _wordsNum.text=[NSString stringWithFormat:@"%lu",WordsNumber-subCharTotal];
    }
    else{
        _wordsNum.text=[NSString stringWithFormat:@"%lu",WordsNumber-charTotal];
    }
}
/**
 计算输入的字符长度
 */
- (NSUInteger)countCharacterLength:(NSString *)test
{
    __block NSUInteger total = 0;
    [test enumerateSubstringsInRange:NSMakeRange(0, test.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString * _Nullable substring, NSRange substringRange, NSRange enclosingRange, BOOL * _Nonnull stop) {
        total++;
    }];
    DDLogInfo(@"当前输入字符总数%lu",(unsigned long)total);
    return total;
}

Emoji参考资料：
1.iOS 对于表情符号 emoji被截断问题
https://blog.csdn.net/bug_delete/article/details/90694630
2.深入理解Emoji(一) —— 字符集，字符集编码
https://www.jianshu.com/p/ca191d9bdcc0
3.深入理解Emoji(二) —— 字节序和BOM
https://www.jianshu.com/p/ca191d9bdcc0
4.深入理解Emoji(三) —— Emoji详解
https://juejin.im/post/5c00b31a5188251d9e0c4a59