取字符串的十六进制编码（注意！一个emoje也是一个编码）

因为和硬件交互需要传递16进制的emoje并且显示
试过以下方式
unichar ch = [str characterAtIndex:0];
发现有规则限制（不能大于\ UFFFF的Unicode值）
后自己写以下方法单独处理

- (void)printTest{
    NSString * inputString = @"🌞:";
    NSString *uniStr = [NSString stringWithUTF8String:[inputString UTF8String]];
    NSData *uniData = [uniStr dataUsingEncoding:NSNonLossyASCIIStringEncoding];
    NSString *goodStr = [[NSString alloc] initWithData:uniData encoding:NSUTF8StringEncoding] ;    
    NSLog(@"%@",goodStr);   

    [self coverteStingToArray:inputString completed:^(NSArray *array) {
        for(int i = 0 ; i < array.count; i ++){
            NSString *byteString = [array objectAtIndex:i];
            //取UTF-32编码
            NSData *data = [byteString dataUsingEncoding:NSUTF32LittleEndianStringEncoding];
            uint32_t unicode;
            [data getBytes:&unicode length:sizeof(unicode)];
            NSLog(@"%x", unicode);
        }
    }];    
}
//逐个取出字符
- (void)coverteStingToArray:(NSString *)inputString completed:(void (^)(NSArray *array))completeBlock{
    NSMutableArray  *returnArray = [NSMutableArray new];
    NSRange fullRange = NSMakeRange(0, inputString.length);
    [inputString enumerateSubstringsInRange:fullRange
                          options:NSStringEnumerationByComposedCharacterSequences
                       usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop)
    {
        [returnArray addObject:substring];
        if(substringRange.location + substringRange.length ==  inputString.length){
            completeBlock(returnArray);
        }
    }];
}

参考链接
https://www.jianshu.com/p/d46d0fdbad93