Cascade ComboBox depends on first one

Question

Hello I got a problem. 

 

I am trying to make an easy app for intern use.

And I have no clue how to make one combobox depend on other.

 

I have read a lot of articles but no one was clear for me.

I guess I started totally wrong. 

 

Here is my code: 

 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Data;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Imaging;

using System.Windows.Navigation;

using System.Windows.Shapes;

using System.Data.SqlClient;

namespace CTSys

{

public partial class MainWindow : Window

{

public MainWindow()

{

InitializeComponent();

CmbGroup();

CmbTool();

}

string con = "Data Source=DESKTOP-HN7S1G3\\SQLEXPRESS;Initial Catalog=Sample;Integrated Security=true;";

// Fills tool groups

private void CmbGroup ()

{

SqlConnection sqlcon = new SqlConnection(con);

// Opens SQL Connection

try

{

sqlcon.Open();

string query = "SELECT * FROM tool_group";

SqlCommand cmd = new SqlCommand(query, sqlcon);

SqlDataReader dr = cmd.ExecuteReader();

while (dr.Read())

{

string name = dr.GetString(1);

cmbGroup.Items.Add(name);

}

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

}

//Fills Tools depends on Tool Group

private void CmbTool()

{

SqlConnection sqlcon = new SqlConnection(con);

// Opens SQL Connection

try

{

sqlcon.Open();

string query = "SELECT * FROM tools";

SqlCommand cmd = new SqlCommand(query, sqlcon);

SqlDataReader dr = cmd.ExecuteReader();

while (dr.Read())

{

string name = dr.GetString(2);

cmbTool.Items.Add(name);

}

sqlcon.Close();

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

}

}

}