Help with user controls within PlaceHolders.

[CroCrew]

Hello all,

Thanks for looking at my post and thank to anyone that provides me with the help I am looking for.

I dynamically load user controls from a default page but when a postback fires within the user controls I can’t get the selected user control to reload. Hard to explain so I will try to show you what is going on.

Default1.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default1.aspx.vb" Inherits="Default1" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
    <head runat="server"> 
        <title></title> 
    </head> 
    <body> 
        <form id="form1" runat="server"> 
            <asp:PlaceHolder runat="server" ID="myPlaceHolder"> 
                Welcome please select a option. 
            </asp:PlaceHolder> 
            <p> 
                <asp:LinkButton id="LinkButton1" runat="server">Say Hello</asp:LinkButton><br /> 
                <asp:LinkButton id="LinkButton2" runat="server">Say Goodbye</asp:LinkButton><br /> 
            </p> 
        </form> 
    </body> 
</html>

Default1.aspx.v b

Partial Class Default1 
    Inherits System.Web.UI.Page 
  
    Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click 
        myPlaceHolder.Controls.Clear() 
        myPlaceHolder.Controls.Add(LoadControl("Hello.ascx")) 
    End Sub 
  
    Protected Sub LinkButton2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton2.Click 
        myPlaceHolder.Controls.Clear() 
        myPlaceHolder.Controls.Add(LoadControl("Goodbye.ascx")) 
    End Sub 
End Class

When I click on the link “Say Hello” the user control “Hello.asc x” does load in the placeholder just fine.

Hello.ascx

<%@ Control Language="VB" AutoEventWireup="false" CodeFile="Hello.ascx.vb" Inherits="Hello" %> 
What is your name? <asp:TextBox ID="TextBox1" runat="server"/> 
&nbsp;&nbsp; 
<asp:Button ID="Button1" runat="server" Text="Answer" /> 
<br /> 
<br /> 
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>

Hello.ascx.vb

Partial Class Hello 
    Inherits System.Web.UI.UserControl 
  
    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click 
        Label1.Text = "Hello " & TextBox1.Text 
    End Sub 
End Class

When I enter my name and click the “Answer” button the page reloads back to the original state with no user control loaded. Why is the “Hello.asc x” user control not loaded with “Lable1” populated with the information for the click event from the code behind event?

Can someone tell me why?

Thanks,
CroCrew~

[yarbrough40]

Hey cro. try regestering the control in the default page

<%@ Register TagPrefix="MyControl" TagName="MyControl" Src="~/Hello.ascx" %>

then when you load the control in the code behind, call it by its tag "MyControl"
-see if that works

[CroCrew]

Thanks for the reply yarbrough40.

I know how to use the <%@ Register %> to add includes. But, to dynamically loading specific user controls at run time within a placeholder using the <%@ Register %> I have not done.

I would think that after registering the control I could just use this syntax: myPlaceHolder.C ontrols.Add(Loa dControl(MyCont rol)) within the click event but that does not work.

Do I have the correct syntax?

Default1.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default1.aspx.vb" Inherits="Default1" %> 
<%@ Register TagPrefix="MyControl" TagName="MyControl" Src="~/Hello.ascx" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<html xmlns="http://www.w3.org/1999/xhtml">  
    <head runat="server">  
        <title></title>  
    </head>  
    <body>  
        <form id="form1" runat="server">  
            <asp:PlaceHolder runat="server" ID="myPlaceHolder">  
                Welcome please select a option.  
            </asp:PlaceHolder>  
            <p>  
                <asp:LinkButton id="LinkButton1" runat="server">Say Hello</asp:LinkButton>
            </p>  
        </form>  
    </body>  
</html>

Default1.aspx.v b

Partial Class Default1  
    Inherits System.Web.UI.Page  
  
    Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click  
        myPlaceHolder.Controls.Clear()  
        myPlaceHolder.Controls.Add(LoadControl(MyControl))  
    End Sub  
End Class

Thanks,
CroCrew~

[yarbrough40]

hmmm - I see. I also have not done what you are attempting. later on today I will see if I can get it to work if you are still failing. In your code behind try first instantiating the new control and then adding that.
If you were to put it in the page directly as opposed to loading it at runtime I believe it would need to look like this:

<MyControl:MyControl runat="server" />

so an instantiation of exactly this somehow might do the trick

[CroCrew]

Correct. That is how I add my headers and footers to my pages. But, as you can see I am trying to dynamically loading specific user controls at run time within a placeholder using a click event.

I will keep on trying things to see if I can figure it out.

I do thank you for your help. If you figure out anything please let me know.

Thanks again,
CroCrew~

[yarbrough40]

do you know for sure that the placeholder is the issue? if you try to load your control elsewhere in the form does it still fail to persist?

[CroCrew]

Using <MyControl:MyCo ntrol runat="server" /> to add a control on a page would work but, not how I want it to work.

The issue is I want to change out the text within the placeholder to a user control and within the user control there is a textbox that when you enter your name in it and click the submit button the code behind on the user control would process something. As it is now after you click the submit button in the user control the parent page reloads to its original state.

[CroCrew]

What I am trying to do is from the parent page have a few links that would do a postback and based on the link chosen a user control would then be loaded within a placeholder on the parent page. All that works fine.

The part that I just can’t seem to figure out is how to process the code behind for the user control if a click event is fired from the loaded user control. On any postback from a user control all I get is the parent page reloading to its original state.

I am about 65% in thinking it can’t be done.

[yarbrough40]

Ok so I did some playing around. It works if you store the control name in viewstate and then call it back on page load

Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click
        LoadHello()
    End Sub

    Private Sub LoadHello()
        Dim mc As Control = LoadControl("Hello.ascx")
        myPlaceHolder.Controls.Clear()
        myPlaceHolder.Controls.Add(mc)
        ViewState.Add("MyControl", "Hello.ascx")
        SaveViewState()
    End Sub

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If IsPostBack Then
            Dim ControlName As String = ViewState("MyControl")
            If Not ControlName Is Nothing Then
                Dim control As Control = LoadControl(ControlName)
                myPlaceHolder.Controls.Add(control)
            End If
        End If

    End Sub

ROCK!

[CroCrew]

WONDERFUL!! That is exactly what I was looking to do.

Yarbrough40 you ROCK!!

[CroCrew]

Oh and congratulations on your 200 post!

[yarbrough40]

lol! 200 posts with an answer. it's like providence : )

[CroCrew]

After a week of testing I have found a bug but can’t seem to understand why this bug is happening. Below is the code for the two pages and here are the steps to trigger the bug.

Steps:
1. Click on the “Say Hello” LinkButton.
2. Enter your name and click the “Answer” button.
3. You should see a message saying “Hello {your name}”. This works fine.
4. Click on the “Say Hello” LinkButton again.
5. Enter your friends name and click the “Answer” button.
6. You should see a message saying “Hello {your friend’s name}” but it does not unless you type your friends name again.

The bug is after the second time you click on the “Say Hello” LinkButton.

Any advice on fixing this bug?

Thanks,
CroCrew~

Default.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<html xmlns="http://www.w3.org/1999/xhtml">  
    <head id="Head1" runat="server">  
        <title></title>  
    </head>  
    <body>  
        <form id="form1" runat="server">  
            <asp:PlaceHolder runat="server" ID="myPlaceHolder">  
                Welcome please select a option.  
            </asp:PlaceHolder>  
            <p>  
                <asp:LinkButton id="LinkButton1" runat="server">Say Hello</asp:LinkButton><br />  
            </p>  
        </form>  
    </body>  
</html>

Default.aspx.vb

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If IsPostBack Then
            Dim ControlName As String = ViewState("MyControl")
            If Not ControlName Is Nothing Then
                Dim control As Control = LoadControl(ControlName)
                myPlaceHolder.Controls.Clear()
                myPlaceHolder.Controls.Add(control)
            End If
        End If
    End Sub

    Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click
        Dim mc As Control = LoadControl("Hello.ascx")
        myPlaceHolder.Controls.Clear()
        myPlaceHolder.Controls.Add(mc)
        ViewState.Add("MyControl", "Hello.ascx")
        SaveViewState()
    End Sub
End Class

Hello.ascx

<%@ Control Language="VB" AutoEventWireup="false" CodeFile="Hello.ascx.vb" Inherits="Hello" %>
What is your name? <asp:TextBox ID="TextBox1" runat="server"/>  
&nbsp;&nbsp;  
<asp:Button ID="Button1" runat="server" Text="Answer" />  
<br />  
<br />  
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>

Hello.ascx.vb

Partial Class Hello
    Inherits System.Web.UI.UserControl

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Label1.Text = "Hello " & TextBox1.Text
    End Sub
End Class

[yarbrough40]

it looks as though the problem is occurring from re-adding the control after the control has been added. What then occurs is that you end up Clearing the controls and adding it back (in the page load) THEN Clearing and adding again (in the Link Button Event). Unsure why, but when this happens, your button click event in the ascx control does not fire.
Try these two adjustments and see if it suites your needs:

Default.aspx.vb

 Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click

        Dim ControlName As String = ViewState("MyControl")

        If ControlName Is Nothing Then
            Dim mc As Control = LoadControl("Hello.ascx")
            myPlaceHolder.Controls.Clear()
            myPlaceHolder.Controls.Add(mc)
            ViewState.Add("MyControl", "Hello.ascx")
            SaveViewState()
            mc.EnableViewState = True
        End If

    End Sub

Hello.ascx.vb

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Label1.Text = "Hello " & TextBox1.Text
        TextBox1.Text = ""
    End Sub

[CroCrew]

Thanks Yarbrought40,

That works when reloading the “same” control. But, when I add the ability for more controls it will only load the first control.

See below code (Goodbye.ascx is the same as Hello.ascx but is just says goodbye instead):

Default.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<html xmlns="http://www.w3.org/1999/xhtml">  
    <head id="Head1" runat="server">  
        <title></title>  
    </head>  
    <body>  
        <form id="form1" runat="server">  
            <asp:PlaceHolder runat="server" ID="myPlaceHolder">  
                Welcome please select a option.  
            </asp:PlaceHolder>  
            <p>  
                <asp:LinkButton id="LinkButton1" runat="server">Say Hello</asp:LinkButton><br />  
                <asp:LinkButton id="LinkButton2" runat="server">Say Goodbye</asp:LinkButton><br />  
            </p>  
        </form>  
    </body>  
</html>

Default.aspx.vb

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If IsPostBack Then
            Dim ControlName As String = ViewState("MyControl")
            If Not ControlName Is Nothing Then
                Dim control As Control = LoadControl(ControlName)
                myPlaceHolder.Controls.Clear()
                myPlaceHolder.Controls.Add(control)
            End If
        End If
    End Sub

    Sub SetControl(ByVal ControlPage As String)
        Dim ControlName As String = ViewState("MyControl")

        If ControlName Is Nothing Then
            Dim mc As Control = LoadControl(ControlPage)
            myPlaceHolder.Controls.Clear()
            myPlaceHolder.Controls.Add(mc)
            ViewState.Add("MyControl", ControlPage)
            SaveViewState()
            mc.EnableViewState = True
        End If
    End Sub

    Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click
        SetControl("Hello.ascx")
    End Sub

    Protected Sub LinkButton2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton2.Click
        SetControl("Goodbye.ascx")
    End Sub
End Class