How to get the Data in the database to mu UI form using Connection string in Vb.Net

Question

I am using a Combobox and I need to fill the data from my sql server database using connection string.

What I have Tried:

Imports System
Imports System.Collections.Generic
Imports System.Web
Imports System.Xml
Imports System.Windows.Forms
Imports System.Data.SqlClient
Imports System.Configuration


Public Class Form1

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim VB = ConfigurationManager.ConnectionString["HMDB"].ConnectionString
        Using Con = New SqlConnection(VB)
            Dim SqlText = "Select DocEntry from dbo.Master1"
            Dim cmd = New SqlCommand(SqlText, Con)
            Con.Open()
            ComboBox1.DataSource = cmd.ExecuteReader()
            ComboBox1.DataBind()

        End Using
    End Sub
End Class

App.Config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configuration>
    <connectionStrings>
      <add name ="HMDB"
           connectionString ="Data Source=DESKTOP-68VGRJG;Database=master;integrated security =SSPI"/>
            </connectionStrings>
</configuration>
</configuration> 

I don't know where I have made a mistake. I need to call the data in sql server to the combo box and I have to make it visible.

Answer 1

You may want to populate your comboBox once your form is loaded, not on the change to comboBox event.

Write the same code in Form1() constructor.

public Form1()
        {
            InitializeComponent();
             Dim VB = ConfigurationManager.ConnectionString["HMDB"].ConnectionString
            Using Con = New SqlConnection(VB)
            Dim SqlText = "Select DocEntry from dbo.Master1"
            Dim cmd = New SqlCommand(SqlText, Con)
            Con.Open()
            ComboBox1.DataSource = cmd.ExecuteReader()
            ComboBox1.DataBind()
            End Using           
        }