Why all dropdownlist_SelectedIndexChanged events trigger only after button click?

Question

I have a simple ASP.NET Application. And On one of my pages all dropdownlist_SelectedIndexChanged events trigger only after I click save button.

This is part of my code behidn:

protected void ddlTimekeeperOffice_SelectedIndexChanged(object sender, EventArgs e)
        {
            CheckUniqueCombination();
        }

        protected void ddlTkprDepartment_SelectedIndexChanged(object sender, EventArgs e)
        {
            CheckUniqueCombination();
        }

        protected void ddlTkprSummaryTitle_SelectedIndexChanged(object sender, EventArgs e)
        {
            CheckUniqueCombination();
        }

this is 3 dropdowns

protected void btnSave_Click(object sender, EventArgs e)
        {
            trTimekeeperRow.Visible = true;
        }

and a save button.

When I select anything in dropdowns > Nothing happens Then I click save button and before save_click it goes through every ddl_selectedindexchanged.

Why?

Answer 1

Make sure AutoPostBack property of the dropdown controls is true.