iOS字符截取（表情漢字）

TextField、TextView 輸入，超過設定長度自動截取符合規定長度。一個漢字至關於兩個字符。添加一個類別，實現以下：

//字符長度限制
- (BOOL)stringLengthValidateWithLimitLength:(NSInteger)maxLength{
    
    BOOL result = YES;
    if ([self countOfBytes] > maxLength)
        result = NO;
    return  result;
    
}

- (NSInteger)countOfBytes {
    
    return [self dataUsingEncoding:CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000)].length;
    
}

- (NSString *)substringWithLength:(NSInteger)maxLength{
    
    __block NSInteger leng = 0;
    __block NSString *result = nil;
    [self enumerateSubstringsInRange:NSMakeRange(0, self.length)
                             options:NSStringEnumerationByComposedCharacterSequences
                          usingBlock:^(NSString * _Nullable substring, NSRange substringRange, NSRange enclosingRange, BOOL * _Nonnull stop)
    {
        leng += [substring dataUsingEncoding:CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000)].length;
        if (leng >= maxLength) {
            result = [self substringWithRange:NSMakeRange(0, enclosingRange.location + enclosingRange.length)];
            *stop = YES;
        }
        
    }];
    return result;
    
}