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I want to implement a finite state machine (FSM) inside a typical ASP.NET web form. I would like the FSM "engine" to be automatically invoked each time a Page_Load() event happens - which is easy enough - but I also want the engine to receive information about which event caused the Page_Load() to occur. The difficulty is that in an ASP.NET web form, a user-controlled event, such as a button click, can cause the page to reload, but the event handler for the button click itself does not get invoked until after the Page_Load() event fires. As far as I can tell, the Page_Load() handler itself does not contain any information about what user event caused the page to reload. I would prefer not to have to explicitly invoke the FSM engine from within each event-handler method. Is there any way to accomplish this? -- to have Page_Load(), or some other stage in the page life-cycle, "know" what particular user action caused the page to reload?

Robert Rotstein
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  • It looks like the solution is here: "http://stackoverflow.com/questions/20838022/eventtarget-is-empty-on-postback-of-button-click" – Robert Rotstein Dec 31 '16 at 23:20

1 Answers1

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ASP.NET Web forms will store it in a parameter in the Request object. You can get it like this:

// Find the control name
string nameOfControlWhichCausedPostback = page.Request.Params.Get("__EVENTTARGET");

Then find the control with that name:

if (!String.IsNullOrWhitespace(nameOfControlWhichCausedPostback ))
{
    var ctrl = page.FindControl(nameOfControlWhichCausedPostback );
}
CodingYoshi
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  • I'm surprised to see that __EVENTTARGET is not in the list of Page.Request.Params. The button click is definitely invoking the Page_Load(), but that item is not there. – Robert Rotstein Dec 31 '16 at 23:02
  • http://stackoverflow.com/questions/20838022/eventtarget-is-empty-on-postback-of-button-click – Robert Rotstein Dec 31 '16 at 23:18