Loading one user control after another has loaded - ASP.NET WebForms

Question

I have a UserControl A that has to be loaded first and after that completes loading, I need to load a UserControl B.

I prefer to add both these user controls on the page at compile time (would like to avoid dynamic loading if possible).

If I add user controls on the page at compile time and set visible to false for User Control B, does it still execute the B's code behind? I can then set the visibility to true after loading User Control A
Should I be using events/delegates for notifying the completion of loading User Control A?

Why does Control A need to be loaded before Control B? UserControls shouldn't be designed to interact with other UserControls unless they are nested controls or composite controls. Can you explain your design further? — Adam Spicer

Phill Phill · Accepted Answer · 2010-12-10T02:03:45

Don't load everything in the page event in control b, just put a method on control b to be called. Then add an event to control a which the page consumes, when the event is raised, call the load method on control b.

Edit: SampleCode

Ok so for example, create

a ASPX page
2x user controls

Put both user controls into the aspx page.

    <cc:control1 runat="server" id="control_one" />
    <cc:control2 runat="server" id="control_two" />

Then in control 1, create a delegate and event.

    public delegate void MyCustomEvent (EventArgs args);
    public event MyCustomEvent MyEvent;

    protected void Page_Load(object sender, EventArgs e)
    {
        MyEvent(e);
    }

So I have the event raised on page load. So you would have your logic in there thats required, when your done, calls MyEvent event.

In the page you want to add a handler for that event so when it's called you can do something with it.

    protected override void OnInit(EventArgs e)
    {
        control_one.MyEvent += new WebUserControl1.MyCustomEvent(control_one_MyEvent);
        base.OnInit(e);
    }

    void control_one_MyEvent(EventArgs args)
    {
        control_two.MyCustomLoad();
    }

So when the page is initialized I add the event handler. In the event handler I call a custom method on the second control to load stuff.

Then in the second control I have:

    public void MyCustomLoad()
    {
        //Stuff only loaded when event is raised and calls this method.
    }

So this allows control 1 to load something, say it's done, when the page knows it's done, it can tell control 2 to do something.

Edit: After discussing this with a friend I'll explain what I mean by controlling the order.

You cannot control the order of page-life-cycle events. i.e: You can't have Control A, run through all it's page-life-cycle events, then once it's done, have Control B run through all it's page-life-cycle events.

If you do-away with the page life cycle, you can do a degree, as my example above shows, create a way of controlling the order in which the controls are rendered. By raising an event(s) at certain points when Control A is finished, you can tell Control B to do something.

The intermediate between the two controls is the page which handles the events raised by Control A which calls a method on Control B. You (well you can hack around to do it) can't specifically make Control A tell Control B to do something because that creates a direct dependency between the two controls which is bad.

Loading one user control after another has loaded - ASP.NET WebForms

4 Answers