delete image in gridview on windows phone

I made a gridview that contains the images. Images are stored in a thumb folder in windows phone 8.1. I want to delete a selected image from gridview and thumb folder on my windows phone

The xaml:

<GridView
                            x:Name="itemGridView"
                            AutomationProperties.AutomationId="ItemsGridView"
                            AutomationProperties.Name="Items"
                            TabIndex="1"                               
                            IsSwipeEnabled="false"
                            Padding="50,30,0,0"
                            HorizontalAlignment="Left"
                            Foreground="{x:Null}" RightTapped="itemGridView_RightTapped" SelectedItem="None">
                            <GridView.ItemTemplate>
                                <DataTemplate>
                                    <Grid Height="400" Width="285" Margin="20,20,0,0">
                                        <Grid.ColumnDefinitions>
                                            <ColumnDefinition Width="Auto"/>
                                            <ColumnDefinition Width="*"/>
                                        </Grid.ColumnDefinitions>
                                        <Image Source="{Binding Image}" AutomationProperties.Name="{Binding Name}" x:Name="myImage" Stretch="Uniform"/>

                                    </Grid>
                                </DataTemplate>
                            </GridView.ItemTemplate>
                        </GridView>

The code:

private async void itemGridView_RightTapped(object sender, RightTappedRoutedEventArgs e)
        {
            StorageFolder thumbfolder = await installedLocation.CreateFolderAsync("thumb", CreationCollisionOption.OpenIfExists);

            Book hapusbuku = this.itemGridView.SelectedItem as Book;
            MessageDialog messageDialog;
            String deskripsi = String.Format("Yakin menghapus buku {0}?", hapusbuku.Name);
            messageDialog = new MessageDialog(deskripsi, "Hapus Buku");
            // Add commands and set their callbacks
            messageDialog.Commands.Add(new UICommand("Batal", (command) =>
            {
                //rootPage.NotifyUser("The 'Don't install' command has been selected.", NotifyType.StatusMessage);
            }));

            messageDialog.Commands.Add(new UICommand("Hapus", async (command) =>
            {
                try
                {
                    thumbfolder.GetFileAsync(hapusbuku.Name + ".png");
                    await thumb.DeleteAsync();
                    this.itemGridView.SelectedItem = itemGridView.Items[0];

                }
                catch
                {
                    this.itemGridView.SelectedItem = itemGridView.Items[0];
                }
            }));
            // Show the message dialog
            await messageDialog.ShowAsync();
        }

but after I press the "hapus" button, the picture is not deleted and still in the gridview. Please help me