Question

class Program
{
    static Socket m_sock;

    static void Main(string[] args)
    {
        Socket m_sock= new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        .
        .
        .
        m_sock.Connect(ipendLocalhost);
        SendRequest("command");
    }

    static void SendRequest(string sCommand)
    {
       .
       .
     **m_sock.Send(szCommand, iBytesToSend, SocketFlags.None);**
     }

说到Send方法，我得到NullReferenceException。在调试中（我添加了m_sock来监视）我看到当程序进入SendRequest方法时，m_sock变为null。我不明白为什么会这样，问题出在哪里。请帮忙。

Answer 1

m_sock是在Main和class级别内部定义的，您不必在Main中再次定义它，只需初始化它，如：

static void Main(string[] args)
    {
        m_sock= new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

请注意Socket已删除。

目前，您的Main方法正在初始化本地m_sock，这就是您的类级m_sock保持为空的原因，稍后当您在静态方法中访问它时，您将获得异常。

Answer 2

因为您在Main

中声明了另一个m_sock

Socket m_sock=new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

将其更改为

m_sock=new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

Answer 3

问题来自您在Main中的声明，Socket m_sock=隐藏了类级别的字段。

static Socket m_sock;
static void Main(string[] args)
{
    Socket m_sock = new Socket // Create a new Socket in m_sock from the Main method only
    SendRequest("command");
}

static void SendRequest(string sCommand)
{
  m_sock.Send() // Uses the socket at the Class level, which is not initialized
}

将初始化更改为

static void Main(string[] args)
{
    m_sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    m_sock.Connect(ipendLocalhost);

    SendRequest("command");
}

或删除类级别声明并将其作为变量传递

static void Main(string[] args)
{
    Socket m_sock= new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    m_sock.Connect(ipendLocalhost);

    SendRequest(m_sock, "command");
}

static void SendRequest(Socket m_sock, string sCommand)
{
   m_sock.Send(szCommand, iBytesToSend, SocketFlags.None);
}

控制台程序，静态方法，套接字变为空

3 个答案: