获取选定的项目列表框WP8.1 C＃

Question

I try to get the item to export to pdf
When I am holding the item, it shows me a menuFlyout Export to PDF
so I try to get the index to be able to export it.
Xaml

<Page
x:Class="WritePad_CSharpSample.ReadWritePadNoteList"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:WritePad_CSharpSample"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

<Grid>
    <StackPanel Grid.Row="0" Margin="12,17,0,28">
        <TextBlock Text="Read All Notes with listbox" Margin="9,-7,0,0" FontSize="28"/>
    </StackPanel>

    <ListBox Background="Transparent" Margin="6" Height="auto" BorderThickness="2" MaxHeight="580" Grid.Row="1" x:Name="listBoxobj" SelectionChanged="listBoxobj_SelectionChanged">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid Width="350" >
                    <Border Margin="5" BorderBrush="White" BorderThickness="1">
                        <Grid Holding="Grid_Holding" VerticalAlignment="Stretch">
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                            </Grid.RowDefinitions>

                            <FlyoutBase.AttachedFlyout>
                                <MenuFlyout>
                                    <MenuFlyoutItem x:Name="EditButton"
                                            Text="Export To PDF"
                                            Click="EditButton_Click"
                                                    />
                                </MenuFlyout>
                            </FlyoutBase.AttachedFlyout>
                            <TextBlock Margin="5,0,0,0" Grid.Row="0" x:Name="NameTxt" TextWrapping="Wrap" Text="{Binding Name}" FontSize="28" Foreground="White"/>
                            <TextBlock HorizontalAlignment="Right" Margin="0,0,35,0" Grid.Row="3" x:Name="CreateddateTxt" Foreground="White" FontSize="18" TextWrapping="Wrap" Text="{Binding CreationDate}" />
                        </Grid>
                    </Border>
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

</Grid>

<Page.BottomAppBar>
    <CommandBar>
        <CommandBar.PrimaryCommands>
            <AppBarButton Label="New" Click="AddNewNoteClick" />
            <AppBarButton x:Name="deleteAppBarButton" Label="Delete All" Click="DeleteAllNoteClick" />
        </CommandBar.PrimaryCommands>
    </CommandBar>
</Page.BottomAppBar>

C#

    using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Text;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Storage;
using Windows.System;
using Windows.UI.Popups;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using WritePad_CSharpSample.Helpers;
using WritePad_CSharpSample.Model;

namespace WritePad_CSharpSample
{

    public sealed partial class ReadWritePadNoteList : Page
    {
        ObservableCollection<WritePadFileContent> DB_ContactList = new ObservableCollection<WritePadFileContent>();

        int Selected_ContactId = 0;
        DatabaseHelperClass Db_Helper = new DatabaseHelperClass();
        WritePadFileContent currentcontact = new WritePadFileContent();
        string name = "";
        string desc = "";
        public ReadWritePadNoteList()
        {
            this.InitializeComponent();
            this.Loaded += ReadWritePadFileContentList_Loaded;
        }

        private void ReadWritePadFileContentList_Loaded(object sender, RoutedEventArgs e)
        {
            ReadAllWritePadFileContent dbnote = new ReadAllWritePadFileContent();
            DB_ContactList = dbnote.GetAllContacts();//Get all DB contacts 
            if (DB_ContactList.Count > 0)
                deleteAppBarButton.IsEnabled = true;
            else
                deleteAppBarButton.IsEnabled = false;
            listBoxobj.ItemsSource = DB_ContactList.OrderByDescending(i => i.Id).ToList();//Binding DB data to LISTBOX and Latest contact ID can Display first. 

        }




    protected override void OnNavigatedTo(NavigationEventArgs e)
            { }
private void AddNewNoteClick(object sender, RoutedEventArgs e)
        {


    Frame.Navigate(typeof(MainPage));
    }

private void listBoxobj_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    int SelectedContactID = 0;
    if (listBoxobj.SelectedIndex != -1)
    {
        WritePadFileContent listitem = listBoxobj.SelectedItem as WritePadFileContent;//Get slected listbox item contact ID 
        Frame.Navigate(typeof(DeleteUpdateNote), SelectedContactID = listitem.Id);

    }
}

private async void DeleteAllNoteClick(object sender, RoutedEventArgs e)
{
        var dialog = new MessageDialog("Are you sure you want to remove all your data ?");
        dialog.Commands.Add(new UICommand("No", new UICommandInvokedHandler(Command)));
        dialog.Commands.Add(new UICommand("Yes", new UICommandInvokedHandler(Command)));
        await dialog.ShowAsync();
    }

    private void Command(IUICommand command)
    {
        if (command.Label.Equals("Yes"))
        {
            DatabaseHelperClass Db_Helper = new DatabaseHelperClass();
            Db_Helper.DeleteAllWritePadFileContent();//delete all DB contacts 
            DB_ContactList.Clear();//Clear collections 
            //Btn_Delete.IsEnabled = false;
            deleteAppBarButton.IsEnabled = false;
            listBoxobj.ItemsSource = DB_ContactList;
        }
    }





    private void Grid_Holding(object sender, HoldingRoutedEventArgs e)
        {
            FrameworkElement senderElement = sender as FrameworkElement;
            FlyoutBase flyoutBase = FlyoutBase.GetAttachedFlyout(senderElement);

            flyoutBase.ShowAt(senderElement);
        }

        private async void EditButton_Click(object sender, RoutedEventArgs e)
        {

            WritePadFileContent listitem = (sender as ListBox).DataContext as WritePadFileContent;
            MessageDialog messageDialog = new MessageDialog(listitem.Name.ToString());
            await messageDialog.ShowAsync();
            //pdf code work
        }
    }
}

The Exception here, it return null, so any help to get the item when I am holding from the listbox?

Answer 1

When you tap and hold, the ListViewItem doesn't get selected, so SelectedItem will always be null. Instead, you should get the value of the DataContext from the MenuFlyoutItem, like this:

private async void EditButton_Click(object sender, RoutedEventArgs e)
    {
        WritePadFileContent listitem = (e.OriginalSource as MenuFlyoutItem).DataContext as WritePadFileContent;
        MessageDialog messageDialog = new MessageDialog(listitem.Name.ToString());
        await messageDialog.ShowAsync();



        //code for export to pdf, it works
    }