Working with DropDownList SelectedIndex Changed Event

Let's make a scenario to use a SelectedIndexChanged event of a dropdownlist control by binding it with a database.

Create a Table

Here we are taking four attributes.

Add Content

Connection String

Setting Connection String in the web.config file.

Front-End

Here is how our aspx page looks like.

Code

Find the aspx.cs code below.
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Data;
  4. using System.Data.SqlClient;
  5. using System.Configuration;
  6. using System.Web;
  7. using System.Web.UI;
  8. using System.Web.UI.WebControls;
  10. namespace StateManagement
  11. {
  12. public partial class WebForm2 : System.Web.UI.Page
  13. {
  15. SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString);
  16. protected void Page_Load(object sender, EventArgs e)
  17. {
  19. if (!IsPostBack)
  20. {
  21. String strQuery = "SELECT distinct (City) FROM UserDetails";
  23. SqlCommand cmd = new SqlCommand();
  24. cmd.CommandType = CommandType.Text;
  25. cmd.CommandText = strQuery;
  26. cmd.Connection = con;
  27. try
  28. {
  29. con.Open();
  30. DropDownList1.DataSource = cmd.ExecuteReader();
  31. DropDownList1.DataTextField = "City";
  32. DropDownList1.DataValueField = "City";
  33. DropDownList1.DataBind();
  34. // DropDownList2.SelectedIndex = 1;
  35. }
  36. catch (Exception ex)
  37. {
  38. throw ex;
  39. }
  40. finally
  41. {
  42. con.Close();
  43. // con.Dispose();
  44. }
  45. }
  47. }
  49. protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
  50. {
  52. String strQuery = "SELECT distinct (Designation) FROM UserDetails";
  54. SqlCommand cmd = new SqlCommand();
  55. cmd.CommandType = CommandType.Text;
  56. cmd.CommandText = strQuery;
  57. cmd.Connection = con;
  58. try
  59. {
  60. con.Open();
  61. DropDownList2.DataSource = cmd.ExecuteReader();
  62. DropDownList2.DataTextField = "Designation";
  63. DropDownList2.DataValueField = "Designation";
  64. DropDownList2.DataBind();
  65. // DropDownList2.SelectedIndex = 1;
  66. }
  67. catch (Exception ex)
  68. {
  69. throw ex;
  70. }
  71. finally
  72. {
  73. con.Close();
  74. con.Dispose();
  75. }
  77. }
  79. protected void Button2_Click(object sender, EventArgs e) //Gridview binding
  80. {
  81. SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString);
  82. SqlCommand cmd = new SqlCommand("select * from UserDetails where City = '" + DropDownList1.SelectedValue + "' and Designation='"+DropDownList2.SelectedValue+"'" , con);
  83. SqlDataAdapter Adpt = new SqlDataAdapter(cmd);
  84. DataTable dt = new DataTable();
  85. Adpt.Fill(dt);
  86. GridView1.DataSource = dt;
  87. GridView1.DataBind();
  88. }
  90. protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
  91. {
  92. //code for DropDownList2_SelectedIndexChanged
  93. }
  95. }
  96. }

Output

Select the City DropDownList.

Select the Designation DropDownList.

Click the Search button to display details in the GridView.
Summary

Great! We have implemented binding with a DropDownlist, worked with the SelectedIndexChanged event of DropDownList and GridView binding.

Thanks.