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Saturday, October 25, 2008

Dynamically loading UserControl in ASP.Net

I gathered information from the following sources to come up with the following:

4 Guys from Rolla
ASP.Net
CodeProject

First the UserControl:

This is how it looks like in VS Designer:


The code is as follows:

<%@ Control Language="vb" AutoEventWireup="false" Codebehind="ucAckFrm.ascx.vb" Inherits="testWeb.ucAckFrm" TargetSchema="http://schemas.microsoft.com/intellisense/ie5" %>
<asp:panel id="PaneCtrl" runat="server">
 <asp:Label id="lblCtrlName" runat="server"></asp:Label>
 <BR>
 <asp:Panel id="paneDisp" runat="server">
<asp:Label id="lblMsg" runat="server"></asp:Label><BR><BR>
<asp:Button id="btnAck" runat="server" Text="Acknowledge"></asp:Button>
<asp:Button id="btnReject" runat="server" Text="Reject"></asp:Button>  
<asp:TextBox id="txtReason" runat="server"></asp:TextBox><BR>
<asp:Label id="lblErrMsg" runat="server" ForeColor="Red"></asp:Label>
<HR>
</asp:Panel>
</asp:panel>

The code behind is as follows:

Public Class ucAckFrm
    Inherits System.Web.UI.UserControl

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
     Private Sub InitializeComponent()

    End Sub
    Protected WithEvents lblMsg As System.Web.UI.WebControls.Label
    Protected WithEvents btnAck As System.Web.UI.WebControls.Button
    Protected WithEvents btnReject As System.Web.UI.WebControls.Button
    Protected WithEvents txtReason As System.Web.UI.WebControls.TextBox
    Protected WithEvents lblCtrlName As System.Web.UI.WebControls.Label
    Protected WithEvents lblErrMsg As System.Web.UI.WebControls.Label
    Protected WithEvents PaneCtrl As System.Web.UI.WebControls.Panel
    Protected WithEvents paneDisp As System.Web.UI.WebControls.Panel

    'NOTE: The following placeholder declaration is required by the Web Form Designer.
    'Do not delete or move it.
    Private designerPlaceholderDeclaration As System.Object

    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

    Public Event AckClick As EventHandler
    Public Event RjctClick As EventHandler

    Public Property RjctReason() As String
        Get
            Return txtReason.Text
        End Get
        Set(ByVal Value As String)
            txtReason.Text = Value
        End Set
    End Property

    Public Sub setMainPane(ByVal pVisible As Boolean)
        PaneCtrl.Visible = pVisible
    End Sub

    Public Sub setDispPane(ByVal pVisible As Boolean)
        paneDisp.Visible = pVisible
    End Sub

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        lblCtrlName.Text = Me.ID
    End Sub

    Private Sub btnAck_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAck.Click
        RaiseEvent AckClick(Me, e)
    End Sub


    Private Sub btnReject_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReject.Click
        Dim tmpStr As String

        tmpStr = Trim(txtReason.Text)

        If tmpStr.Length > 0 Then
            RaiseEvent RjctClick(Me, e)
        Else
            lblErrMsg.Text = "Reject Reason cannot be blank"
        End If
    End Sub
End Class

The main aspx page:


The code:

<%@ Register TagPrefix="uc1" TagName="ucAckFrm" Src="ucAckFrm.ascx" %>
<%@ Page Language="vb" AutoEventWireup="false" Codebehind="TestPage.aspx.vb" Inherits="testWeb.WebForm1"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
 <HEAD>
  <title>WebForm1</title>
  <meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
  <meta content="Visual Basic .NET 7.1" name="CODE_LANGUAGE">
  <meta content="JavaScript" name="vs_defaultClientScript">
  <meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
 </HEAD>
 <body>
  <form id="Form1" method="post" runat="server">
   <asp:label id="lblMsg" runat="server"></asp:label><br>
   <asp:textbox id="txtMsg" runat="server"></asp:textbox><br>
   <br>
   <asp:button id="btnSubmit" runat="server" Text="Submit"></asp:button><br>
   <asp:Label id="lblErrMsg" runat="server" ForeColor="Red"></asp:Label><br>
   <hr>
   <br>
   <uc1:ucAckFrm id="DefAck" runat="server"></uc1:ucAckFrm><br>
   <asp:PlaceHolder id="pHolder" runat="server"></asp:PlaceHolder></form>
 </body>
</HTML>

The code behind:

Public Class WebForm1
    Inherits System.Web.UI.Page

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
     Private Sub InitializeComponent()

    End Sub
    Protected WithEvents lblMsg As System.Web.UI.WebControls.Label
    Protected WithEvents txtMsg As System.Web.UI.WebControls.TextBox
    Protected WithEvents btnSubmit As System.Web.UI.WebControls.Button
    Protected WithEvents defAck As ucAckFrm
    Protected WithEvents pHolder As System.Web.UI.WebControls.PlaceHolder
    Protected WithEvents lblErrMsg As System.Web.UI.WebControls.Label

    'NOTE: The following placeholder declaration is required by the Web Form Designer.
    'Do not delete or move it.
    Private designerPlaceholderDeclaration As System.Object

    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

    Dim vStr As String
    Dim ackArray As New ArrayList

    Private Sub PageInit2(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        Dim ctrlCnt, tmpStr As String
        Dim loopCnt, ackCnt As Integer
        Dim vAckCtrl As ucAckFrm
        Dim ctrl As Control

        ctrlCnt = Request.Item("opt")
        vStr = ctrlCnt

        If IsNumeric(vStr) Then
            ackCnt = CInt(vStr)
            If ackCnt > 0 Then
                For loopCnt = 0 To (ackCnt - 1)
                    ctrl = LoadControl("ucAckFrm.ascx")
                    tmpStr = "Ack_" & loopCnt
                    ctrl.ID = tmpStr
                    vAckCtrl = CType(ctrl, ucAckFrm)
                    AddHandler vAckCtrl.AckClick, AddressOf AckHandlerAck
                    AddHandler vAckCtrl.RjctClick, AddressOf AckHandlerRjct

                    ackArray.Add(vAckCtrl)
                    pHolder.Controls.Add(ctrl)
                Next
            End If
        End If

        AddHandler defAck.AckClick, AddressOf AckHandlerAck
        AddHandler defAck.RjctClick, AddressOf AckHandlerRjct

    End Sub


    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If IsPostBack = False Then
            Try
                lblMsg.Text += "ctrlCnt value is " & vStr
            Catch ex As Exception
                lblErrMsg.Text += "<br>" & ex.Message
            End Try

        End If

    End Sub


    Private Sub AckHandlerAck(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Dim idName As String

        idName = UCase(CType(sender, Control).ID)

        lblMsg.Text += "<br>Acknowledge by " & idName
    End Sub

    Private Sub AckHandlerRjct(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Dim idName, reason As String
        Dim handledCtrl As ucAckFrm

        idName = UCase(CType(sender, Control).ID)
        handledCtrl = CType(sender, ucAckFrm)
        reason = handledCtrl.RjctReason

        lblMsg.Text += "<br>Rejected by " & idName & " due to " & reason
    End Sub
End Class

In this example, to simplify testing, I use the url parameter opt to determine how many times I want to load the usercontrol. In the following example, I loaded it twice - i.e. ?opt=2


Key points I learn from the articles are:
  • Init will be called each time the page is refreshed.
  • View State is loaded after the init phase before the page load phase.
  • To load the control, we actually use the .ascx file using Page.LoadControl
  • After loading the control, we need to use CType to change back to the class defined in the codebehind for the usercontrol so we can access the properties, events etc for the user control.
Other Notes on this example:
  • In the example above, I assigned the ID for each of the controls that are dynamically loaded, this is actually for a project I am working on where the requestor will specify how many persons will be informed of a request made. Each person receiving the request will then have an option to either acknowledge the request or reject it. In that situation, I will then name each of the controls with the role for each receipient.
  • I added the mainPane and dispPane to provide an option if to either hide the whole control or to display on the header (but not used in the example above).
  • I use a try catch and throw to practice Error handling I wrote in my previous article.
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