字符串判断含有emoji

- (BOOL)ydx_isEmoji {
    NSString *string = self;
    if ([string length]<2)
    {
        return NO;
    }
    
    static NSCharacterSet *_variationSelectors;
    _variationSelectors = [NSCharacterSet characterSetWithRange:NSMakeRange(0xFE00, 16)];
    
    if ([string rangeOfCharacterFromSet: _variationSelectors].location != NSNotFound)
    {
        return YES;
    }
    const unichar high = [string characterAtIndex:0];
    // Surrogate pair (U+1D000-1F9FF)
    if (0xD800 <= high && high <= 0xDBFF)
    {
        const unichar low = [string characterAtIndex: 1];
        const int codepoint = ((high - 0xD800) * 0x400) + (low - 0xDC00) + 0x10000;
        return (0x1D000 <= codepoint && codepoint <= 0x1F9FF);
        // Not surrogate pair (U+2100-27BF)
    }
    else
    {
        return (0x2100 <= high && high <= 0x27BF);
    }
}