C#窗体列表框选定的索引已更改事件在加载窗体并单击按钮时触发

我正在编写一个程序，允许用户使用用户在TextBox中键入的客户名称搜索客户订单，搜索结果显示在ListBox控件中用户不必从列表框中选择名称，客户订单显示在DataGridView中问题是，一旦客户单击搜索按钮，SelectedIndex更改事件引发并导致程序崩溃。

private void btnSearch_Click(object sender, EventArgs e)
{
   string Query = "SELECT  CustomerID, CompanyName FROM Customers WHERE (CompanyName ”+                “LIKE'%"+ txtSearch.Text + "%')";
   clsDataTools.cmdComand = clsDataTools.con.CreateCommand();
   clsDataTools.cmdComand.CommandText = Query;
   clsDataTools.dtaDataAdapter = new SqlDataAdapter();
   clsDataTools.dtaDataAdapter.SelectCommand = clsDataTools.cmdComand;
   dsOrdersByCusName = new DataSet();
   clsDataTools.con.Close();
   clsDataTools.con.Open();
   clsDataTools.dtaDataAdapter.Fill(dsOrdersByCusName);
   clsDataTools.con.Close();
   dsOrdersByCusName.Tables[0].TableName = "OrderBCusName";
   lstResults.DataSource = dsOrdersByCusName.Tables[0];
   lstResults.DisplayMember = "CompanyName";
   lstResults.ValueMember = "CustomerID";
}
private void lstResults_SelectedIndexChanged(object sender, EventArgs d)
{
    string Query = "SELECT  * From Orders WHERE CustometID  = '" 
                   + lstResults.SelectedValue  
                   + "'";
    dataGridDataSet = new DataSet();
    clsDataTools.dtaDataAdapter = new SqlDataAdapter();
    clsDataTools.cmdComand = clsDataTools.con.CreateCommand();
    clsDataTools.cmdComand.CommandText = Query;
    clsDataTools.con.Close();
    clsDataTools.con.Open();
    clsDataTools.dtaDataAdapter.SelectCommand = clsDataTools.cmdComand;
    clsDataTools.dtaDataAdapter.Fill(dataGridDataSet);
    clsDataTools.con.Close();
    dataGridDataSet.Tables[0].TableName = "Orders";
    dgvCusOrders.DataSource = dataGridDataSet;
    dgvCusOrders.DataMember = dataGridDataSet.Tables["Orders"].ToString();
  }

我真的不明白为什么当我点击搜索按钮时SelctedIndexChanged事件会触发——也许我遗漏了什么？

private void btnSearch_Click(object sender, EventArgs e)
{
    //Remove the handler 
    this.lstResults.SelectedIndexChanged -= lstResults_SelectedIndexChanged;
    // 
    // Your code
    //
    this.lstResults.SelectedIndexChanged += lstResults_SelectedIndexChanged; // Add the handler 
}