Remove Item from ComboBox if selected in another ComboBox in Windows Forms using C# and VB.Net

Hi Akram.19,

Check this example. Now please take its reference and correct your code.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Linq;

VB.Net

Imports System.Data
Imports System.Data.SqlClient
Imports System.Linq

Code

C#

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private DataTable dtSelected { get; set; }

    private void Form1_Load(object sender, EventArgs e)
    {

        comboBox1.DataSource = GetComboData();
        comboBox1.ValueMember = "CategoryID";
        comboBox1.DisplayMember = "CategoryName";

        comboBox2.DataSource = GetComboData();
        comboBox2.ValueMember = "CategoryID";
        comboBox2.DisplayMember = "CategoryName";

        comboBox3.DataSource = GetComboData();
        comboBox3.ValueMember = "CategoryID";
        comboBox3.DisplayMember = "CategoryName";
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (comboBox1.SelectedIndex > 0)
        {
            GetSelectedData();
            DataTable dt = GetRowsAfterDelete();
            comboBox2.DataSource = dt;
            comboBox2.ValueMember = "CategoryID";
            comboBox2.DisplayMember = "CategoryName";
        }
    }

    private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (comboBox2.SelectedIndex > 0)
        {
            GetSelectedData();
            DataTable dt = GetRowsAfterDelete();
            comboBox3.DataSource = dt;
            comboBox3.ValueMember = "CategoryID";
            comboBox3.DisplayMember = "CategoryName";
        }
    }

    public DataTable GetComboData()
    {
        string conString = "Server=.;Database=Northwind;UID=sa;PWD=pass@123;";
        string query = "SELECT CategoryID,CategoryName FROM Categories";
        using (SqlConnection con = new SqlConnection(conString))
        {
            SqlCommand cmd = new SqlCommand(query);
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    DataRow dr = dt.NewRow();
                    dr["CategoryID"] = 0;
                    dr["CategoryName"] = "Select";
                    dt.Rows.InsertAt(dr, 0);

                    return dt;
                }
            }
        }
    }

    private DataTable GetRowsAfterDelete()
    {
        DataTable dt = GetComboData();
        DataTable dtResult = dt.Copy();
        foreach (DataRow row in dtSelected.Rows)
        {
            DataRow dr = dt.Select("CategoryID=" + row["CategoryID"]).FirstOrDefault();
            if (dr != null)
            {
                dt.Rows.Remove(dr);
            }
        }

        return dt;
    }

    private void GetSelectedData()
    {
        dtSelected = new DataTable();
        dtSelected.Columns.Add("CategoryID");
        dtSelected.Columns.Add("CategoryName");
        dtSelected.Rows.Clear();
        if (comboBox1.SelectedIndex > 0)
        {
            DataRowView drv1 = (DataRowView)comboBox1.SelectedItem;
            dtSelected.Rows.Add((drv1.Row as DataRow).ItemArray);
        }
        if (comboBox2.SelectedIndex > 0)
        {
            DataRowView drv2 = (DataRowView)comboBox2.SelectedItem;
            dtSelected.Rows.Add((drv2.Row as DataRow).ItemArray);
        }
        if (comboBox3.SelectedIndex > 0)
        {
            DataRowView drv3 = (DataRowView)comboBox3.SelectedItem;
            dtSelected.Rows.Add((drv3.Row as DataRow).ItemArray);
        }
    }
}

VB.Net

Private Property dtSelected As DataTable

Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
    comboBox1.DataSource = GetComboData()
    comboBox1.ValueMember = "CategoryID"
    comboBox1.DisplayMember = "CategoryName"
    comboBox2.DataSource = GetComboData()
    comboBox2.ValueMember = "CategoryID"
    comboBox2.DisplayMember = "CategoryName"
    comboBox3.DataSource = GetComboData()
    comboBox3.ValueMember = "CategoryID"
    comboBox3.DisplayMember = "CategoryName"
End Sub

Private Sub comboBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    If comboBox1.SelectedIndex > 0 Then
        GetSelectedData()
        Dim dt As DataTable = GetRowsAfterDelete()
        comboBox2.DataSource = dt
        comboBox2.ValueMember = "CategoryID"
        comboBox2.DisplayMember = "CategoryName"
    End If
End Sub

Private Sub comboBox2_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    If comboBox2.SelectedIndex > 0 Then
        GetSelectedData()
        Dim dt As DataTable = GetRowsAfterDelete()
        comboBox3.DataSource = dt
        comboBox3.ValueMember = "CategoryID"
        comboBox3.DisplayMember = "CategoryName"
    End If
End Sub

Public Function GetComboData() As DataTable
    Dim conString As String = "Server=.;Database=Northwind;UID=sa;PWD=pass@123;"
    Dim query As String = "SELECT CategoryID,CategoryName FROM Categories"
    Using con As SqlConnection = New SqlConnection(conString)
        Dim cmd As SqlCommand = New SqlCommand(query)
        Using sda As SqlDataAdapter = New SqlDataAdapter()
            cmd.Connection = con
            sda.SelectCommand = cmd
            Using dt As DataTable = New DataTable()
                sda.Fill(dt)
                Dim dr As DataRow = dt.NewRow()
                dr("CategoryID") = 0
                dr("CategoryName") = "Select"
                dt.Rows.InsertAt(dr, 0)
                Return dt
            End Using
        End Using
    End Using
End Function

Private Function GetRowsAfterDelete() As DataTable
    Dim dt As DataTable = GetComboData()
    Dim dtResult As DataTable = dt.Copy()
    For Each row As DataRow In dtSelected.Rows
        Dim dr As DataRow = dt.Select("CategoryID=" & row("CategoryID")).FirstOrDefault()
        If dr IsNot Nothing Then
            dt.Rows.Remove(dr)
        End If
    Next

    Return dt
End Function

Private Sub GetSelectedData()
    dtSelected = New DataTable()
    dtSelected.Columns.Add("CategoryID")
    dtSelected.Columns.Add("CategoryName")
    dtSelected.Rows.Clear()
    If comboBox1.SelectedIndex > 0 Then
        Dim drv1 As DataRowView = CType(comboBox1.SelectedItem, DataRowView)
        dtSelected.Rows.Add((TryCast(drv1.Row, DataRow)).ItemArray)
    End If
    If comboBox2.SelectedIndex > 0 Then
        Dim drv2 As DataRowView = CType(comboBox2.SelectedItem, DataRowView)
        dtSelected.Rows.Add((TryCast(drv2.Row, DataRow)).ItemArray)
    End If
    If comboBox3.SelectedIndex > 0 Then
        Dim drv3 As DataRowView = CType(comboBox3.SelectedItem, DataRowView)
        dtSelected.Rows.Add((TryCast(drv3.Row, DataRow)).ItemArray)
    End If
End Sub

Screenshot