Question

I see some people are using Page_Load and Page_PreRender in same aspx page. Can I exactly know why do we need to invoke both the methods in same asp.net page?

Please see the code below,

    protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            dprPager.ButtonClickPager += new EventHandler(dprPager_ButtonClickPager);

            if (!Page.IsPostBack)
            {
              InitPager();

            }
        }
        catch (Exception ex)
        {

        }

    }

    protected void Page_PreRender(object sender, EventArgs e)
    {
        erMsg.Visible = !string.IsNullOrEmpty(lblError.Text);
    }

Answer 1

It depends on your requirements.

Page Load : Perform actions common to all requests, such as setting up a database query. At this point, server controls in the tree are created and initialized, the state is restored, and form controls reflect client-side data. See Handling Inherited Events.

Prerender :Perform any updates before the output is rendered. Any changes made to the state of the control in the prerender phase can be saved, while changes made in the rendering phase are lost. See Handling Inherited Events.

Reference: Control Execution Lifecycle MSDN

Try to read about

ASP.NET Page Life Cycle Overview ASP.NET

Control Execution Lifecycle

Regards