Dynamic Loading of ASP.NET User Controls


Partial Class _Default
    Inherits System.Web.UI.Page

    ' Declare 2 variable to handle user control after postback
    Dim controlID As String = "MyUserControl"
    Dim Shared createAgain As Boolean = False


    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        ' Create instance of the UserControl SimpleControl
        Dim ucSimpleControl As usercontrol_SimpleControl = LoadControl("~/usercontrol/SimpleControl.ascx")

        ' Set the Public Properties
        ucSimpleControl.FirstName.Text = "Milind"
        ucSimpleControl.LastName.Text = "Chavan"

        ' Create Event Handler for btnPost Click 
        AddHandler ucSimpleControl.btnPostClk, AddressOf ucSimpleControl_onPostClk

        ' Add the SimpleControl to Placeholder
        Placeholder1.Controls.Add(ucSimpleControl)

        ' Add the instance of the SimpleControl to Session Variable
        Session.Add((Session.Count + 1).ToString(), ucSimpleControl)

        ' Set createAgain = true
        createAgain = True
    End Sub

    Protected Sub ucSimpleControl_onPostClk(ByVal sender As Object, ByVal e As System.EventArgs)

        Dim ucSimpleControl As usercontrol_SimpleControl = DirectCast(DirectCast(sender, System.Web.UI.WebControls.Button).Parent, usercontrol_SimpleControl)
        lblUser.Text = ("Welcome " + ucSimpleControl.FirstName.Text & " ") + ucSimpleControl.LastName.Text

    End Sub

    Protected Sub Page_PreInit(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreInit
        Dim ctrl As Control = GetPostBackControl(Me.Page)

        ' Check if the postback is caused by the button 
        ' Titled "Click to Create a Dynamic Control"
        ' OR
        ' createAgain field is true 
        ' which means a call is made to the server while the 
        ' user control is active  

        If (ctrl IsNot Nothing AndAlso ctrl.ClientID = Button1.ClientID) OrElse createAgain Then
            'should be set before the CreateUserControl method
            createAgain = True

            CreateUserControl(controlID)
        End If

        ' Check if the postback is caused by the button 
        ' Titled "Click to Create a Dynamic Control"
        ' OR
        ' createAgain field is true 
        ' which means a call is made to the server while the 
        ' user control is active  

        If (ctrl IsNot Nothing AndAlso ctrl.ClientID = Button1.ClientID) OrElse createAgain Then
            'should be set before the CreateUserControl method
            createAgain = True

            CreateUserControl(controlID)
        End If


    End Sub

    Protected Function GetPostBackControl(ByVal pg As Page) As Control
        Dim ctl1 As Control = Nothing

        Try
            Dim ctrlName As String = pg.Request.Params.Get("__EVENTTARGET")

            If ctrlName IsNot Nothing AndAlso ctrlName <> [String].Empty Then
                ctl1 = Page.FindControl(ctrlName)
            Else
                Dim cph As ContentPlaceHolder = DirectCast(Page.FindControl("Main"), ContentPlaceHolder)
                Dim i As Integer = 0, len As Integer = Page.Request.Form.Count
                While i < len
                    Dim ctl As String() = Page.Request.Form.AllKeys(i).Split("$"c)
                    If ctl.Length > 2 Then
                        ctl1 = TryCast(cph.FindControl(ctl(2)), System.Web.UI.WebControls.Button)
                    End If

                    If ctl1 IsNot Nothing Then
                        Exit While
                    End If
                    i += 1
                End While
            End If

        Catch ex As Exception
            Throw ex
        End Try

        Return ctl1
    End Function


    Protected Sub CreateUserControl(ByVal controlID As String)
        ' createAgain field is set to true in the OnPreInit method
        ' when the 'Create User Control' button is clicked 

        ' the createAgain field is used to check if the
        ' user control is on the page before the call 
        ' if so create the control again and add it to the
        ' Control Hierarchy again
        Try
            If createAgain AndAlso Placeholder1 IsNot Nothing Then
                If Session.Count > 0 Then
                    Placeholder1.Controls.Clear()
                    For i As Integer = 0 To Session.Count - 1
                        Select Case Session(i).ToString()
                            Case "ASP.usercontrol_simplecontrol_ascx"
                                If True Then
                                    ' Create instance of the UserControl SimpleControl
                                    Dim ucSimpleControl As usercontrol_SimpleControl = TryCast(LoadControl("~/usercontrol/SimpleControl.ascx"), usercontrol_SimpleControl)

                                    ' Set the Public Properties
                                    ucSimpleControl.FirstName.Text = DirectCast(Session(i), usercontrol_SimpleControl).FirstName.Text
                                    ucSimpleControl.LastName.Text = DirectCast(Session(i), usercontrol_SimpleControl).LastName.Text

                                    'Create Event Handler for btnPost Click 
                                    AddHandler ucSimpleControl.btnPostClk, AddressOf ucSimpleControl_onPostClk

                                    'Add the SimpleControl to Placeholder
                                    Placeholder1.Controls.Add(ucSimpleControl)
                                    Exit Select
                                End If
                        End Select
                    Next
                End If
            End If
        Catch ex As Exception
            Throw ex
        End Try
    End Sub

End Class