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I have a custom DataFormWebPart that renders some content based on an XSLT. Inside the XSLT I have a button that does a postback like so:

<input type="button" value="..." name="..." 
       onclick="javascript: {ddwrt:GenFireServerEvent('__name')}" />

I don't really know how to treat this event at the server side and the docs I could find are not very useful.

How do I treat this on the server side - in the WebPart or (preferably) in the Page that contains my WebPart?

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It's interesting question. If you examine the code of RaisePostBackEvent method of DataFormWebPart class you will see the processing of such actionas as _connect, _update, _insert, _commit, _cancel, _refresh, _delete, _redirect and some others. For example on __redirect command DataFormWebPart executes the following code:

else if (this.DoesPostbackEqualEvent(str2, "__redirect", true, out modifiedCommandStr))
            this.PerformRedirect(modifiedCommandStr);

And the PerformRedirect function is defined as:

private void PerformRedirect(string commandSubString)
    {
      if (this.DesignMode)
        return;
      SPUtility.Redirect(new Uri(HttpContext.Current.Request.Url, this.UnEscapeDelims(commandSubString)).AbsoluteUri, SPRedirectFlags.Trusted | SPRedirectFlags.DoNotEncodeUrl, this.Context);
    }

It looks like you cannot define and process such "events" - it's only to instruct the DataFormWebPart what to do on postback. And finally it looks like you can parametrize used command.

As for workarounds on porocessing such events - I suppose these events can be handled on server side in traditional way for postbacks:

private void HandlePostback() {
  if (this.Page.Request["__EVENTTARGET"] == "__myCommand") {
    // do your processing
  }
}

You can place such handler in custom webpart without UI and place it on the same page, for example.

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I've eventually added my code in the DataFormWebPart.PreprocessPostBackEvent method using custom action names that I then replace on method exit with __refresh.

It works for the particular case I'm having; might not work for everybody (in which case Alex Boev's answer might be useful).

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