LinkButton CommandName and CommandArgument

Question

I'm having trouble understanding CommandName and CommandArgument associated with an ASP.NET LinkButton. I have read this article - http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.button.commandname.aspx and other questions on this site.

I guess my questions are - what exactly is a "Command"? Can a CommandName basically be any text? I see "Sort" and "Submit" as examples. And as for CommandArgument, this is just used to further specify the type of "Command". Correct? Thanks very much for your help.

Answer 1

A Command can be anything you want it to be.

The basic idea is that if you say have a repeater, and in that repeater you have multiple options, you can give each option a different CommandName. The CommandArgument would then be based on the unique identifier of the line.

Then on the post-back you can check which CommandName was fired and based on that use the value in the CommandArgument

For Example, the mark-up could look something like...

<asp:Repeater runat="server" id="myRepeater">
  <ItemTemplate>
    <div>
      <asp:LinkButton runat="server" id="lnkEdit" CommandName="edit" 
        CommandArgument="<%#Container.DataItem.Id%>" Text="Edit" 
        OnClick="OnClickHandler" />
      <asp:LinkButton runat="server" id="lnkDelete" CommandName="delete" 
        CommandArgument="<%#Container.DataItem.Id%>" Text="Delete"
        OnClick="OnClickHandler" />
    </div>
  </ItemTemplate>
</asp:Repeater>

Then your post-pack handler could check to see which one was clicked...

Protected Sub OnClickHandler(ByVal sender As Object, ByVal e As EventArgs)
  Dim lnk as LinkButton = CType(sender,LinkButton)
  Select Case lnk.CommandName
    Case "edit"
      EditItem(lnk.CommandArgument)
    Case "delete"
      DeleteItem(lnk.CommandArgument)
  End Select
End Sub

Answer 2

CommandName can be any string yes. But beware! ASP.NET will treat certain strings in a special way. For example if you have a Button control in a GridView column with a CommandName of "delete" it will raise the OnDeleting event and the CommandArgument will have been set to the row index of the GridViewRow that the button is in. Otherwise as others have posted you can use the CommandName and CommandArgument however best suits your circumstances.

typically you will set the CommandArgument to be the row index of the control's parent container during binding, and the CommandName to be something meaningful to your application domain, such as "UpdateFoo." You then use this in the OnRowCommand event handler to determine which button has been clicked and therefore what business logic to execute.