InvokeRequired returns false when expecting true?

Question

I have 2 classes form1 and handleClient class , There is one method in form1 which have code to displays data in textbox , when I called this method in same class it is working but if called in handleClient class this method doesnt works.
why this happens , please help me.
thanks .

here is my code,

in form1 class

public void AppendTxtdata(string myval)

{

    try

    {

          if (InvokeRequired)

         {

              this.Invoke(new Action<string>(AppendTxtdata), new object[] { myval });

              return;

        }

           txtdata.Text += myval;

     }

   catch { }

}

I call this method in handleClient in startCLient method in this way, 

 

public void startClient(TcpClient inClientSocket, string clineNo)

{

       this.clientSocket = inClientSocket;

       inClientSocket.NoDelay = true;

       this.clNo = clineNo;

       new Thread(GetData).Start();

}

public void GetData() // to run server //

{

       con.Open();

       this.f = new Form1();

try

{

      NetworkStream networkStream = clientSocket.GetStream();

      for (int p = 0; p >= 0; p++)

     {

         byte[] b = new byte[100];

         int k = networkStream.Read(b, 0, b.Length);

         f.AppendTxtdata("The Data from Client ( " + clNo + " ) Recieved..." +              Environment.NewLine);

      for (int i = 0; i < k; i++)

     {

        f.AppendTxtdata("" + Convert.ToChar(b[i]));

      }

      f.AppendTxtdata(Environment.NewLine);

       var j = b.Length - 1;

       while (b[j] == 0)

       {

           --j;

        }

      var temp = new byte[j + 1];

       Array.Copy(b, temp, j + 1);

        string res = System.Text.Encoding.ASCII.GetString(temp);