Cascading ComboBox In Winforms Windows Forms C# VB.NET

This example explains How To Create Cascading ComboBox Dependent On One Another In WinForms Windows Forms Applications Using C# And VB.Net.


I have used Country, State, City tables from database to populate respective cascading combobox based on selection of country and state.


Drag 3 combobox controls from toolbar on the windows form, write following code to populate comboboxes.

Table schemas are shown below.

Write connection string in app.config file

---

<configuration>

<connectionStrings>

<add name="connectionString"

     connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Cascading.mdf;Integrated Security=True;User Instance=True"

     providerName="System.Data.SqlClient" />

</connectionStrings>

</configuration>

Bind Country ComboBox when Form loads

---

01using System;

02using System.Data;

03using System.Windows.Forms;

04using System.Configuration;

05using System.Data.SqlClient;

06 

07namespace CascadingComboBox

08{

09    public partial class Form1 : Form

10    {

11        string strConn = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;

12        public Form1()

13        {

14            InitializeComponent();

15        }

16 

17        private void Form1_Load(object sender, EventArgs e)

18        {

19            FillCountry();

20        }

21        private void FillCountry()

22        {

23            SqlConnection con = new SqlConnection(strConn);

24            SqlCommand cmd = new SqlCommand();

25            cmd.Connection = con;

26            cmd.CommandType = CommandType.Text;

27            cmd.CommandText = "SELECT CountryID, CountryName FROM Country";

28            DataSet objDs = new DataSet();

29            SqlDataAdapter dAdapter = new SqlDataAdapter();

30            dAdapter.SelectCommand = cmd;

31            con.Open();

32            dAdapter.Fill(objDs);

33            con.Close();

34            cmbCountry.ValueMember = "CountryID";

35            cmbCountry.DisplayMember = "CountryName";

36            cmbCountry.DataSource = objDs.Tables[0];

37        }

38    }

39}

Populate State and City combobox in SelectedIndexChanged event of country,State combobox based on selected IDs

---

01private void cmbCountry_SelectedIndexChanged(object sender, EventArgs e)

02        {

03            if (cmbCountry.SelectedValue.ToString() != "")

04            {

05                int CountryID = Convert.ToInt32(cmbCountry.SelectedValue.ToString());

06                FillStates(CountryID);

07                cmbCity.SelectedIndex = 0;

08            }

09        }

10 

11        private void FillStates(int countryID)

12        {

13            SqlConnection con = new SqlConnection(strConn);

14            SqlCommand cmd = new SqlCommand();

15            cmd.Connection = con;

16            cmd.CommandType = CommandType.Text;

17            cmd.CommandText = "SELECT StateID, StateName FROM State WHERE CountryID =@CountryID";

18            cmd.Parameters.AddWithValue("@CountryID", countryID);

19            DataSet objDs = new DataSet();

20            SqlDataAdapter dAdapter = new SqlDataAdapter();

21            dAdapter.SelectCommand = cmd;

22            con.Open();

23            dAdapter.Fill(objDs);

24            con.Close();

25            if (objDs.Tables[0].Rows.Count > 0)

26            {

27                cmbState.ValueMember = "StateID";

28                cmbState.DisplayMember = "StateName";

29                cmbState.DataSource = objDs.Tables[0];

30            }

31 

32        }

33 

34        private void cmbState_SelectedIndexChanged(object sender, EventArgs e)

35        {

36            int StateID = Convert.ToInt32(cmbState.SelectedValue.ToString());

37            FillCities(StateID);

38        }

39 

40        private void FillCities(int stateID)

41        {

42            SqlConnection con = new SqlConnection(strConn);

43            SqlCommand cmd = new SqlCommand();

44            cmd.Connection = con;

45            cmd.CommandType = CommandType.Text;

46            cmd.CommandText = "SELECT CityID, CityName FROM City WHERE StateID =@StateID";

47            cmd.Parameters.AddWithValue("@StateID", stateID);

48            DataSet objDs = new DataSet();

49            SqlDataAdapter dAdapter = new SqlDataAdapter();

50            dAdapter.SelectCommand = cmd;

51            con.Open();

52            dAdapter.Fill(objDs);

53            con.Close();

54            if (objDs.Tables[0].Rows.Count > 0)

55            {

56                cmbCity.DataSource = objDs.Tables[0];

57                cmbCity.DisplayMember = "CityName";

58                cmbCity.ValueMember = "CItyID";

59 

60            }

61 

62        }

VB.NET CODE

---

01Private Sub Form1_Load(sender As Object, e As EventArgs)

02 FillCountry()

03End Sub

04Private Sub FillCountry()

05 Dim con As New SqlConnection(strConn)

06 Dim cmd As New SqlCommand()

07 cmd.Connection = con

08 cmd.CommandType = CommandType.Text

09 cmd.CommandText = "SELECT CountryID, CountryName FROM Country"

10 Dim objDs As New DataSet()

11 Dim dAdapter As New SqlDataAdapter()

12 dAdapter.SelectCommand = cmd

13 con.Open()

14 dAdapter.Fill(objDs)

15 con.Close()

16 cmbCountry.ValueMember = "CountryID"

17 cmbCountry.DisplayMember = "CountryName"

18 cmbCountry.DataSource = objDs.Tables(0)

19End Sub

20 

21Private Sub cmbCountry_SelectedIndexChanged(sender As Object, e As EventArgs)

22 If cmbCountry.SelectedValue.ToString() <> "" Then

23  Dim CountryID As Integer = Convert.ToInt32(cmbCountry.SelectedValue.ToString())

24  FillStates(CountryID)

25  cmbCity.SelectedIndex = 0

26 End If

27End Sub

28 

29Private Sub FillStates(countryID As Integer)

30 Dim con As New SqlConnection(strConn)

31 Dim cmd As New SqlCommand()

32 cmd.Connection = con

33 cmd.CommandType = CommandType.Text

34 cmd.CommandText = "SELECT StateID, StateName FROM State WHERE CountryID =@CountryID"

35 cmd.Parameters.AddWithValue("@CountryID", countryID)

36 Dim objDs As New DataSet()

37 Dim dAdapter As New SqlDataAdapter()

38 dAdapter.SelectCommand = cmd

39 con.Open()

40 dAdapter.Fill(objDs)

41 con.Close()

42 If objDs.Tables(0).Rows.Count > 0 Then

43  cmbState.ValueMember = "StateID"

44  cmbState.DisplayMember = "StateName"

45  cmbState.DataSource = objDs.Tables(0)

46 End If

47 

48End Sub

49 

50Private Sub cmbState_SelectedIndexChanged(sender As Object, e As EventArgs)

51 Dim StateID As Integer = Convert.ToInt32(cmbState.SelectedValue.ToString())

52 FillCities(StateID)

53End Sub

54 

55Private Sub FillCities(stateID As Integer)

56 Dim con As New SqlConnection(strConn)

57 Dim cmd As New SqlCommand()

58 cmd.Connection = con

59 cmd.CommandType = CommandType.Text

60 cmd.CommandText = "SELECT CityID, CityName FROM City WHERE StateID =@StateID"

61 cmd.Parameters.AddWithValue("@StateID", stateID)

62 Dim objDs As New DataSet()

63 Dim dAdapter As New SqlDataAdapter()

64 dAdapter.SelectCommand = cmd

65 con.Open()

66 dAdapter.Fill(objDs)

67 con.Close()

68 If objDs.Tables(0).Rows.Count > 0 Then

69  cmbCity.DataSource = objDs.Tables(0)

70  cmbCity.DisplayMember = "CityName"

71 

72  cmbCity.ValueMember = "CItyID"

73 End If

74 

75End Sub

Build and run the application.