asp.net/vb.net System.Web.UI.WebControls.RepeaterItemEventArgs question

Question

I'm really new to asp.net so please forgive me if this seems like a really basic question. I have an asp.net page that contains a repeater. Here's the code:

<div class="formRow">
    <asp:Repeater ID="uxStudentFormActive" runat="server">
        <ItemTemplate>
            <span style="font-weight:bold;" ><asp:Literal ID="uxFormName" runat="server" Text="#" /></span><br />
            <asp:TreeView ID="uxFormHistoryList" runat="server" Target="_blank" />              
        </ItemTemplate> 
    </asp:Repeater>
</div>

Here's the sub in my vb.net page that handles uxStudentFormActive.ItemDataBound:

Protected Sub uxStudentFormActive_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles uxStudentFormActive.ItemDataBound

    Dim dr As DataRowView = CType(e.Item.DataItem(), DataRowView)

    If Convert.ToInt32(dr("FormId")) = 29 Then
        ...
    End If

End Sub

I'm not exactly sure how the aspx page interacts with the vb.net page. My question is how do I find out how where the values for e that are being passed to the sub uxStudentFormActive_ItemDataBound in my vb.net page are coming from? Thanks in advance.

Answer 1

From this MSDN article on handling events in ASP.Net:

Events [in ASP.Net] are based on the delegate model...A delegate is a type that holds a reference to a method... An event is a message sent by an object to signal the occurrence of an action. The action could be caused by user interaction, such as a button click, or it could be raised by some other program logic, such as changing a property’s value. The object that raises the event is called the event sender... Data that is associated with an event can be provided through an event data class.

In your case, the event data class is RepeaterItemEventArgs.

To respond to an event, you define an event handler method in the event receiver. This method must match the signature of the delegate for the event you are handling. In the event handler, you perform the actions that are required when the event is raised, such as collecting user input after the user clicks a button. To receive notifications when the event occurs, your event handler method must subscribe to the event.

Reading that, you might say "Well that's well and good, but what does it mean?" In your project, you probably have a property set at the top of your .aspx page named AutoEventWireup. It's probably set to true. This property does what it seems: it automatically wires up your events so that you don't have to. This is how your .aspx page knows how to interact with the code-behind file.

On your .aspx page, you have your repeater control. On your code-behind file, you have your event handler method. Because you have AutoEventWireup set to true, those two things are automatically linked together as long as your event handler method signature matches the signature of the delegate for that event. In this case, that event is ItemDataBound.

To your original question, where do the values of e come from? From the sender!

Protected Sub uxStudentFormActive_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles uxStudentFormActive.ItemDataBound

In this method signature, you have two parameters: sender, and e. As described in the quote above, the sender is the object that raises the event. In your case, this is the RepeaterItem. Since the repeater likely contains many of these objects, the event can be raised multiple times. The event argument, e, is generated from the sender, or the RepeaterItem that was databound and caused the event to fire.

You can read more about the RepeaterItemEventArgs and the data available within on the MSDN.

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As a side note, you can set AutoEventWireup to false and manually wireup the events as described in depth in the link to the MSDN article on the AutoEventWireup property.

Answer 2

Thanks to @Jack for giving me more insight into this. I'm sorry if my OP wasn't more clear, I did understand that the values were coming from the .aspx page, what I was actually asking is where the values that are being passed as e into my sub are being set, how e is being populated with data. The answer came from looking at the repeater id for the repeater I'm asking about, uxStudentFormActive. When I searched for this repeater id my vb.net code behind I found that the data source for the it was defined and bound in the Page_Load sub. Tracking this down lead me to a stored procedure in my database that is being passed session data and e is being set to the results of the stored procedure.