C# How to fix run data show in RichTextBox by instant

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C#

C#4.0

RichTextBox

i have a problem about showing data in RichTextBox by selected tab, but I don't need to show in the selected tab, I need show by RichTextBox for run.

private void btn_Runserver_Click(object sender, EventArgs e)
{
   AddTab();
   StartCMD();

}

private void AddTab()
{
    TabPage newTab = new TabPage((string)cbConfig.SelectedItem);

    RichTextBox rtb = new RichTextBox();

    rtb.Dock = DockStyle.Fill;
    rtb.ScrollBars = System.Windows.Forms.RichTextBoxScrollBars.Vertical;
    rtb.BorderStyle = System.Windows.Forms.BorderStyle.None;
    rtb.BackColor = System.Drawing.Color.White;
    rtb.ReadOnly = true;

    newTab.Tag = rtb;
    newTab.Name = (string)cbConfig.SelectedItem;
    newTab.Controls.Add(rtb);

    tabControl.Controls.Add(newTab);
    tabControl.SelectTab(newTab);
}

private void build_ErrorDataReceived(object sender, DataReceivedEventArgs e)
{
    string strMessage = e.Data;
    if (tabControl.InvokeRequired)
    {
        tabControl.Invoke(new Action(() =>
        {
            RichTextBox rtb = (RichTextBox)tabControl.SelectedTab.Tag;
            rtb.AppendText(strMessage + Environment.NewLine);
            rtb.Select(rtb.Text.Length - 1, 0);
            rtb.ScrollToCaret();
        }));
    }
}

Code RunCMD Form

proc.OutputDataReceived += build_ErrorDataReceived;
proc.BeginOutputReadLine();

Now my problem is that if I run the program and data show in RichTextbox by selected tab, but I need to show data in RichTextbox On RichText Tab Safe

Someone said "change RichTextBox rtb = (RichTextBox)tabControl.SelectedTab.Tag;, don't use SelectedTab", but I not know how to change it accordingly.