LinkBut​​ton CommandName和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.

Answer 3

CommandName is what you actually do when the event is triggered and the CommandArgument and of course is the argument related to process. It makes more sense if you use link buttons in repeater or similar list items. In that case your CommandName can be "Delete", "Edit", "Publish" and for this processes you need to know which record you are dealing with and 'CommandArgument' is your man in this case you can assign it the ID or comma separated data to process.

Of course you can also use this to merge similar events "Sort" is a great example for this as you can give 'CommandArgument' as "Price asc", "Date asc", "Date desc" all your link buttons triggers the event.

Answer 4

As freefaller says, both the CommandName and CommandArgument are just string values.

The reason why is many fold however a click event will just fire the click of a button and you handle that button(s) specifically.

A good example of the use of CommandButtons is imagine you have rows of data, each row has a ability to View, Edit or Delete.

Rather than code for each one seperately, you can use the Command parts and have each row have the CommandArgument of the record ID, and the CommandArgument to be the action you wish to perform; ViewRec, EditRec and DelRec` for example:

protect void cmd_Command(object sender, CommandEventArgs e)
{
    // Example, Redirect to page with action
    response.redirect(string.format("~/record.aspx?id={0}&action={1}", e.commandArgument, e.CommandName);
}

Using this example as a concept, shows that you then only have one section of code to handle multiple options and therefore only one place to maintain etc...