Initiating Requests from one ContentPlaceHolder and Loading/Updating Controls in another

RadAjaxManager could handle all the MasterPage and WebUserControls scenarios no matter the complexity of the application. To prove this, we show you how it can handle a scenario, where loading of WebUserControls is done in contents of MasterPage by RadAjaxManager.

An important point to notice in the following implementation, is the event bubbling approach. We use it because we load dynamically a user control from an action in another loaded user control. So the button click event is bubbled from the user control to the content page, where the first user control is loaded on each page load. Then we determine whether to perform loading of the second user control depending on the command from the button's bubbled event.

Here is the full working code containing a MasterPage, content page and two simple WebUserControls:

<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server" />
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server" />
<asp:Panel ID="Panel1" runat="server">
    <asp:ContentPlaceHolder ID="ContentPlaceHolder2" runat="server" />
</asp:Panel>

This MasterPage has nothing in its code-behind.

Standard content page ASPX:

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server" />
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder2" runat="Server" />

The key content page code-behind:

private Control Content(string id)
{
    return Page.Master.FindControl(id);
}
protected void Page_Load(object sender, System.EventArgs e)
{
    //Load
    Content("ContentPlaceHolder1").Controls.Add(LoadControl("~/Page1.ascx"));
    Content("ContentPlaceHolder1").Controls[1].ID = "UserControl1";
    //Get loaded user control's buttons
    Button AjaxButtonLoad = (Button)Content("ContentPlaceHolder1").FindControl("UserControl1").FindControl("btnLoad");
    Button AjaxButtonClear = (Button)Content("ContentPlaceHolder1").FindControl("UserControl1").FindControl("btnClear");
    //Get the manager and the panel from the MasterPage
    RadAjaxManager AjaxManager = RadAjaxManager.GetCurrent(Page);
    Panel MyPanel = (Panel)Content("Panel1");
    //Add the necessary AJAX settings - buttons update the panel in order to load the second user control there
    AjaxManager.AjaxSettings.AddAjaxSetting(AjaxButtonLoad, MyPanel, null);
    AjaxManager.AjaxSettings.AddAjaxSetting(AjaxButtonClear, MyPanel, null);
}
protected override bool OnBubbleEvent(object source, System.EventArgs args)
{
    CommandEventArgs commandArgs = args as CommandEventArgs;
    //determine whether to load the user control depending on bubbled button command
    if (commandArgs != null)
    {
        if (commandArgs.CommandName == "Load")
        {
            Content("ContentPlaceHolder2").Controls.Add(LoadControl("~/Page2.ascx"));
            Content("ContentPlaceHolder2").Controls[1].ID = "UserControl2";
        }
        else if (commandArgs.CommandName == "Clear")
        {
            //do nothing. the control won't be loaded anyway
        }
    }
    return base.OnBubbleEvent(source, args);
}

Private Function Content(ByVal id As String) As Control
    Return Page.Master.FindControl(id)
End Function

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    'Load
    Content("ContentPlaceHolder1").Controls.Add(LoadControl("~/Page1.ascx"))
    Content("ContentPlaceHolder1").Controls(1).ID = "UserControl1"

    'Get loaded user control's buttons
    Dim AjaxButtonLoad As Button = CType(Content("ContentPlaceHolder1").FindControl("UserControl1").FindControl("btnLoad"), Button)
    Dim AjaxButtonClear As Button = CType(Content("ContentPlaceHolder1").FindControl("UserControl1").FindControl("btnClear"), Button)

    'Get the manager and the panel from the MasterPage
    Dim AjaxManager As RadAjaxManager = RadAjaxManager.GetCurrent(Page)
    Dim MyPanel As Panel = CType(Content("Panel1"), Panel)

    'Add the necessary AJAX settings - buttons update the panel in order to load the second user control there
    AjaxManager.AjaxSettings.AddAjaxSetting(AjaxButtonLoad, MyPanel, Nothing)
    AjaxManager.AjaxSettings.AddAjaxSetting(AjaxButtonClear, MyPanel, Nothing)
End Sub

Protected Overrides Function OnBubbleEvent(ByVal source As Object, ByVal args As System.EventArgs) As Boolean
    Dim commandArgs As CommandEventArgs = TryCast(args, CommandEventArgs)

    'determine whether to load the user control depending on bubbled button command
    If commandArgs IsNot Nothing Then
        If commandArgs.CommandName = "Load" Then
            Content("ContentPlaceHolder2").Controls.Add(LoadControl("~/Page2.ascx"))
            Content("ContentPlaceHolder2").Controls(1).ID = "UserControl2"
        ElseIf commandArgs.CommandName = "Clear" Then
            'do nothing. the control won't be loaded anyway
        End If
    End If

    Return MyBase.OnBubbleEvent(source, args)
End Function

First WebUserControl's code, which is loaded on each page load:

<asp:Button ID="btnLoad" runat="server" Text="Load" CommandName="Load" />
<asp:Button ID="btnClear" runat="server" Text="Clear" CommandName="Clear" />

Code-behind:

public event EventHandler BtnClick;
protected void Button1_Click(object sender, System.EventArgs e)
{
    if (BtnClick != null)
    {
        BtnClick(sender, e);
    }
}

Public Event BtnClick As EventHandler

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnLoad.Click
    RaiseEvent BtnClick(sender, e)
End Sub

And the second WebUserControl, which is loaded when the button "Load" in the first WebUserControl is clicked:

It just shows some text in the ASPX and has nothing in its code-behind.

UserControl2