C#和NetworkStream，发送可以，但接收不起作用

这是源代码，我不明白发生了什么。当我从服务器接收数据，然后写回NetworkStream时，它就工作了，但当我试图在从服务器读取之前先发送时，它不工作：

void BtnConnectClick(object sender, EventArgs e)
{
    TcpClient clientSocket = null;
    NetworkStream networkStream = null;
    try{
        clientSocket = new TcpClient();         
        clientSocket.SendTimeout = 5000;
        clientSocket.ReceiveTimeout = 5000;
        clientSocket.Connect("192.168.0.13",7777);
        networkStream = clientSocket.GetStream();   
        const string strToAndroid = "hi from client";
        char[] carray = strToAndroid.ToCharArray();
        for (int i=0;i<carray.GetLength(0);i++)
        {
            networkStream.WriteByte((byte)carray[i]);
        }
        log("sent to Android = " + strToAndroid);
        string strFromAndroid = "";
        int j=0;
        while (j!=-1)
        {
            try
            {
                j = networkStream.ReadByte();
                if (j!=-1)
                    strFromAndroid += (char)j;
            }
            catch(Exception ex){
                break;
            }
        }
        log("received from Android = " + strFromAndroid);
        networkStream.Close();
        clientSocket.Close();               
    }
    catch(Exception ex){
        log("002:" + ex.Message);
        if (networkStream != null)
            networkStream.Close();
        if (clientSocket != null)
            clientSocket.Close();
    }
}