private void BTN_Import_Click(object sender, EventArgs e)
 {
     if (Window_ImportExport._this == null)
     {
         Window_ImportExport IE = new Window_ImportExport();
         IE._SelectedSkill = _SelectedSkill;
         IE.isExport = false;
         IE.isImport = true;
         IE.Closed += IE_AfterImport;
         IE.Show();
     }
 }
 private void Window_ImportExport_Closed(object sender, EventArgs e)
 {
     _this = null;
 }
 private void Window_ImportExport_Closed(object sender, EventArgs e)
 {
     _this = null;
 }