Question

foreach(Label l in Controls)    // setting all labels' s visbility  on page to true
     l.Visible =true;

But on running ,i am getting following error

Unable to cast object of type 'ASP.admin_master' to type 'System.Web.UI.WebControls.Label'.

Answer 1

If you want the set all labels on the page to visible you need a recursive function.

private void SetVisibility<T>(Control parent, bool isVisible)
{
    foreach (Control ctrl in parent.Controls)
    {
        if(ctrl is T)
            ctrl.Visible = isVisible;
        SetVisibility<T>(ctrl, isVisible);
    }
}

Usage:

SetVisibility<Label>(Page, true);