在iOS中NSData转Byte，见到最多的NSData转Byte的就是

    NSString *string = @"111111";
    NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
    Byte *testByte = (Byte *)[data bytes];

但是这种方法常常是不可行的，这时候就要换个方法了，

    NSString *codeKey = @"111111111";
    NSData *codeKeyData =  [codeKey dataUsingEncoding:NSUTF8StringEncoding];
    Byte codeKeyByteAry[codeKeyData.length];
    for (int i = 0 ; i < codeKeyData.length; i++) {
        NSData *idata = [codeKeyData subdataWithRange:NSMakeRange(i, 1)];
        codeKeyByteAry[i] =((Byte*)[idata bytes])[0];
    }

OK !