void variablePreviewForm_FormClosed(object sender, FormClosedEventArgs e)
 {
     variablePreviewForm = null;
     showVariablePreviewCheckbox.Checked = false;
 }
 private void showVariablePreviewCheckbox_CheckedChanged(object sender, EventArgs e)
 {
     if (!this.isBackgroundRunform)
     {
         if (showVariablePreviewCheckbox.Checked)
         {
             variablePreviewForm = new Controls.VariablePreviewEditorForm(runningSequence.Variables);
             variablePreviewForm.FormClosed += new FormClosedEventHandler(variablePreviewForm_FormClosed);
             variablePreviewForm.Show();
         }
         else
         {
             if (variablePreviewForm != null)
                 variablePreviewForm.Close();
             variablePreviewForm = null;
         }
     }
 }