附加3位以启动nsdata

Question

我无法在nsdata的左侧添加3位（在开始时）。这是我试图转换为iOS的java代码

public byte[] getMessageInFormat(final int MessageType, final int MessageNum, final int MessageNum2, byte[] rawMessage){
        byte[][] result = null;
        byte[] byteStream = new byte[rawMessage.length + 3]; 
        byteStream[0] = (byte) MessageType;
        byteStream[1] = (byte) MessageNum;
        byteStream[2] = (byte) MessageNum2;

        for (int i=0; i<rawMessage.length; i++)
        {
            byteStream[3+i] = rawMessage[i];
        }

    return byteStream;

}

这不起作用

NSData *rawMessage = [@"hello world" dataUsingEncoding:NSASCIIStringEncoding];
NSMutableData * byteStream = [[NSMutableData alloc] init];
        [byteStream appendBytes:&MessageType length:sizeof(MessageType)];
        [byteStream appendBytes:&MessageNum length:sizeof(MessageNum)];
        [byteStream appendBytes:&MessageNum2 length:sizeof(MessageNum2)];
        [byteStream appendData:rawMessage];

Answer 1

[byteStream appendBytes:&MessageType length:sizeof(MessageType)];

没有用，因为MessageType是一个int并将“size of”替换为1个

[byteStream appendBytes:&MessageType length:1];