Question

I have problem passing a variable from a main page containing a user control to the user control itself. Although the passed variable is available generally in the code-behind of the user control the page_load event can’t seem to read it.

My code –

In the main page code-behind:

protected void FindCCFsButton_Click(object sender, EventArgs e)
    {
        if (CustomerDropDown.SelectedIndex != 0)
        { SearchUcCCFList.SetCustID(CustomerDropDown.SelectedValue); }
    }

(SearchUcCCFList is the instance of the user control in the main aspx page).
In the user control code behind:

public partial class ucCCFList : System.Web.UI.UserControl
{
    public string srchCust { get; set; }

    public void SetCustID(string custID)
    {
        srchCust = custID;
        testCustLabel.Text = GetCustID(); //this works
    }

    public string GetCustID()
    {
        return srchCust;
    }

protected void Page_Load(object sender, EventArgs e)
    {
        CCFGridView.DataSource = DAL.SearchCCFs(custID : GetCustID());  //doesn't work
        CCFGridView.DataBind();
        test2CustLabel.Text = GetCustID();  //doesn't work
    }

In the Page_Load event GetCustId() doesn’t return anything (so the records aren’t filtered and all get returned) although it can be read in the methods outside the Page_Load.

I’m probably making a beginners error but any help would be appreciated.

Edit – following Alan’s suggestion in the comments I stepped through the page loading sequence & it appears that the user control’s Page_Load event is running BEFORE the code in the main page’s button click so the variable is not yet available. The sequence after clicking the button is:

1. User control Page_Load runs
2. Code in button event on main page
3. Other code (outside Page_Load) in user control runs hence variable is available here.

This seems a bit weird, is there another way to pass the variable into the user controls Page_Load?

Answer 1

In this case, your click handling even on the main page is called after the user control page load call. Your variable is being set, but not until after your data binding in the user control.

Either switch the user control to declarative binding which will handle calling methods in the correct order for you. Or the easier fix in this case is to change the user control data binding from Page_Load to Page_PreRender, which is called later in the life cycle, after the main page click handling call.

protected void Page_PreRender(object sender, EventArgs e)
{
    CCFGridView.DataSource = DAL.SearchCCFs(custID : GetCustID());  // will work now
    CCFGridView.DataBind();
    test2CustLabel.Text = GetCustID();  // will work now
}

For a more thorough answer, read up on the ASP.NET page life cycle including the interaction with user controls’ life cycle.