DDL_SelectedIndexChanged event

[wild_bill]

When I change the index of a dropdownlist programmatically, the list's SelectedIndexChanged event doesn't fire, when I do it manually it does. Is there a way to force the event programmatically?

[Magiaus]

yeah

ddl.ClearSelection();
ddl.SelectedIndex = 1; //be sure to clear selected first. it will throw an error
ddl_selChange(dll, EventArgs.Empty);

but, I believe the event should fire on it's own it seems to do it for me

[nemaroller]

Ideally, whatever code you have within the selectedIndexChanged event handler would call another procedure to do the work (work procedure). To do so programatically then means you just call the work procedure.

private void InitializeComponent()
		{    
			this.Button1.Click += new System.EventHandler(this.SubmitClickHandler);
			this.Load += new System.EventHandler(this.Page_Load);
			this.dropdownlist1.SelectedIndexChanged +=new EventHandler(DropDownList1SelectedIndexChanged);

		}
		#endregion

		private void SubmitClickHandler(object sender, System.EventArgs e)
		{
			int i = 3;

			//for this example, always true, and calls the worker function
			if (i==3)
				DoTheWork();
		}

		private void DropDownList1SelectedIndexChanged(object sender, EventArgs e)
		{
			//call the worker function
			DoTheWork();
		}

		private void DoTheWork()
		{
            //do the work here
		}

[wild_bill]

Well, I've pulled my hair out all day trying to convert this and that with some success. But, I still can not figure this out, and it's driving me bonkers.
Here's some code I used to test:

Private Sub btnEnter_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEnter.Click
        cboSubYesNo.ClearSelection()
        cboSubYesNo.SelectedIndex = 1
    End Sub
 
    Private Sub cboSubYesNo_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboSubYesNo.SelectedIndexChanged
        MessageBox("I'm Here")
        SubYesNo_PopulateData()
    End Sub

When I click the button, the value changes, but I get no message box. When I manually change the value, I get the message box. I'm totally stumped. All help appreciated.

[Magiaus]

I was wrong the event does not fire.

method 1

Public Class _Default
    Inherits System.Web.UI.Page
    Protected WithEvents ddl As System.Web.UI.WebControls.DropDownList
    Protected WithEvents Button1 As System.Web.UI.WebControls.Button

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

    End Sub

    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form Designer
        'Do not modify it using the code editor.
        InitializeComponent()
    End Sub

#End Region

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If Not IsPostBack Then
            Dim i As Integer = 0
            For i = 0 To 20
                ddl.Items.Add(i.ToString())
            Next
        End If
    End Sub

    Private Sub ddl_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ddl.SelectedIndexChanged
        Response.Write("sel changed")
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ddl.ClearSelection()
        ddl.Items(5).Selected = True
        ddl_SelectedIndexChanged(ddl, EventArgs.Empty)
    End Sub
End Class

Method 2

Public Class _Default
    Inherits System.Web.UI.Page
    Protected WithEvents ddl As System.Web.UI.WebControls.DropDownList
    Protected WithEvents Button1 As System.Web.UI.WebControls.Button

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

    End Sub

    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form Designer
        'Do not modify it using the code editor.
        InitializeComponent()
    End Sub

#End Region

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If Not IsPostBack Then
            Dim i As Integer = 0
            For i = 0 To 20
                ddl.Items.Add(i.ToString())
            Next
        End If
    End Sub

    Private Sub ddl_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ddl.SelectedIndexChanged
        ddlChange()
    End Sub
    Private Sub ddlChange()
        Response.Write("sel changed")
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ddl.ClearSelection()
        ddl.Items(5).Selected = True
        ddlChange()
    End Sub
End Class

Both ways acomplish the same thing.

Method 1 is better because there is no chance of not firing all the code that should fire.

Method 2 is the better because it is the correct way to implement code that needs to be excecuted in more than one location.

If I was working solo I would go with method 2, if I was working with a group of prgrammers I would go with method 1. I would go with Method 1 in a team dev because a lot of times some one will come in make a change and not fully examine all the code; thus you run the risk of having some behavior added directly to the event and not your event method. For a dll especialy it doesn't matter because the EventArgs are useless so it is fine to pass in empty.

Note also that in team dev you could use method 2 and simply place a comment to work with the ddlChange Method...... stylistic chocies suck.....