ApplicationBar.cs

using System.Windows.Controls;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;

namespace AppBar
{
    public partial class PivotPage1 : PhoneApplicationPage
    {
        public PivotPage1()
        {
            InitializeComponent();
            Testpivot.SelectionChanged += Testpivot_SelectionChanged;
        }

        void Testpivot_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            switch ((sender as Pivot).SelectedIndex)
            {
                case 0:
                    ApplicationBar = ((ApplicationBar)this.Resources["Appbar1"]);
                    break;
                case 1:
                    ApplicationBar = ((ApplicationBar)this.Resources["Appbar2"]);
                    break;
            }
        }
    }
}