Vb.net Filling Textbox On Combobox Selected Index Changed With Sql Database

after i programming this code for fill text-box when combo-box selected Index changed i got this error 'Object reference not set to an instance of an object.', whats can i do ??

Solution 1:

You need to assign the cmd.ExecuteReader() to your datareader. Thats where your NullReference is coming from.

datareader = cmd.ExecuteReader()

Solution 2:

PublicSub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) HandlesMyBase.Load
    Dim cn AsNew SqlClient.SqlConnection("Data Source=thee-pc;Initial Catalog=jobportal;Integrated Security=True")
    Dim cmd AsNew SqlClient.SqlCommand
    Dim tbl AsNew DataTable
    Dim da AsNew SqlClient.SqlDataAdapter
    Dim reader As SqlClient.SqlDataReader
    Try
        cn.Open()
        Dim sql AsString
        sql = "select * from Register"
        cmd = New SqlClient.SqlCommand(sql, cn)
        reader = cmd.ExecuteReader
        While reader.Read
            Dim id = reader.Item("cid")
            ComboBox1.Items.Add(id)
        EndWhile
        cn.Close()
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    EndTryEndSubPrivateSub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
    Dim cn AsNew SqlClient.SqlConnection("Data Source=thee-pc;Initial Catalog=jobportal;Integrated Security=True")
    Dim cmd AsNew SqlClient.SqlCommand
    Dim tbl AsNew DataTable
    Dim da AsNew SqlClient.SqlDataAdapter
    Dim reader As SqlClient.SqlDataReader
    Try
        cn.Open()
        Dim sql AsString
        sql = "select * from register where cid ='" + ComboBox1.Text + "'"
        cmd = New SqlClient.SqlCommand(sql, cn)
        reader = cmd.ExecuteReader
        While reader.Read
            TextBox1.Text = reader.Item("cname")
            TextBox2.Text = reader.Item("dob")

        EndWhile
        cn.Close()
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    EndTryEndSub

End Class