WCF service contract and textbox

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C#

I've create a tcp WCF service from windows form. The operationcontract that i implemented will update the text of a textbox. but When client call that operation, the textbox doesn't show that text. How to solve this?

This is my server:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.ServiceModel;
using MiniChat;
namespace MiniChatServer
{
    public partial class FrmMiniChatServer : Form, IServerContract
    {
        private ServiceHost host;
        public FrmMiniChatServer()
        {
            InitializeComponent();
        }
        private void MiniChatServer_Load(object sender, EventArgs e)
        {
            host = new ServiceHost(typeof(FrmMiniChatServer));
            host.Open();
        }
        #region IServerContract Members
        public void ClientToServer(string msg)
        {
            textBox1.Text = "Client: " + msg;
            MessageBox.Show(textBox1.Text);
        }
        #endregion
        private void MiniChatServer_Closed(object sender, FormClosedEventArgs e)
        {
        }
    }
}

And Client

ServerServices.IServerContract server = new ServerServices.ServerContractClient();
server.ClientToServer("message from client");

and contract interfaces

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;
namespace MiniChat
{
    public interface ICallback
    {
        [OperationContract(IsOneWay=true)]
        void ServerToClient(string msg);
    }
    [ServiceContract(CallbackContract=typeof(ICallback))]
    public interface IServerContract
    {
        [OperationContract(IsOneWay=true)]
        void ClientToServer(string msg);
    }

}

In the function:

public void ClientToServer(string msg)
{
    textBox1.Text = "Client: " + msg;
    MessageBox.Show(textBox1.Text);
}

MessageBox.Show(textBox1.Text); show message correctly, but textBox1 doesn't show anything.