SelectedItems in Listview inserted twice

Question

Hi all,

I've a ListView in my App which has an ItemsSource of an List. No I try to insert items of the ListView in the SelectedItems object. What happens is quite weird to me.

When I first navigate to the page, bind the data to the ListView and set the SelectedItems, the number of items in SelectedItems are correct. When I hit a button to load something else, the number of items in SelectedItems is doubled. Every item is in SelectedItems twice. When I bind the data to the ListView again, insert the SelectedItems and hit the button again, everything is fine. i have no idea what's wrong.

This is my ListView:

               <ListView
                    Foreground="{StaticResource MPGETextColor}"
                    SelectionMode="Multiple"
                    x:Name="LVStatChoices"                     
                    Margin="-5,10,0,0"
                    ItemsSource="{Binding}"
                    >
                    <ListView.ItemTemplate>
                        <DataTemplate>
                            <StackPanel>
                                <TextBlock Text="{Binding lblName}"></TextBlock>
                                <TextBlock Text="{Binding lblKey}" Visibility="Collapsed"></TextBlock>
                            </StackPanel>
                        </DataTemplate>
                    </ListView.ItemTemplate>
                </ListView>

OnNavigatedTo I bind the data to the ListView:

LVStatChoices.ItemsSource = names;

and then I insert the selected items like this:

LVStatChoices.SelectedItems.Clear();
                
foreach (lblName ln in LVStatChoices.Items)
{
   if (ln.selectDefault == true && !LVStatChoices.SelectedItems.Contains(ln))
   {
       LVStatChoices.SelectedItems.Add(ln);
   }
}

Currently 8 Items are selected in the UI because 8 items has selectedDefault == true. If I stop debugging after the foreach loop there are 8 items in SelectedItems which is fine. As mentioned above, when I click on a button and stop at

if (LVStatChoices.SelectedItems.Count == 0)

there are 16 Items in SelectedItems.

Again this behaviour occured after migrating my app from Windows 8 to 8.1.

Does anybody has an idea what I'm doing wrong?

Answer 1

Hi,

There is not enough information to detect why your problem occurs. Please upload your project all share a simple project  into skyDrive so that we can test it.

Best wishes！

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Answer 2

Thanks for your reply.

Please download a sample project here.

If you stop at line 47 in MainPage.xaml.cs, you'll see that LVStatChoices.SelectedItems contains 3 objects. If you click on the button an stop at line 52, LVStatChoices.SelectedItems will contain 6 items. It contains every statLabelName item, which has selectDefault = true, twice.

Thanks for your help,

jev

Answer 3

Hi,

I test your project. Your codes seems correct. That's may be a bug in windows store app and I suggest you can edit your code like below:

In XAML:

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <StackPanel Orientation="Vertical" HorizontalAlignment="Left" VerticalAlignment="Top">
            <local:MyListView
                SelectionMode="Multiple"
                x:Name="LVStatChoices"                     
                Width="200"
                Height="400"
                Margin="10"
              
                >
                <local:MyListView.ItemContainerStyle >
                    <Style TargetType="ListViewItem">

                        <Setter Property="IsSelected" Value="{Binding selectDefault, Mode=TwoWay}"/>
                    </Style>
                </local:MyListView.ItemContainerStyle>
                <local:MyListView.ItemTemplate>
                    <DataTemplate>
                        
                            <StackPanel>
                                <TextBlock Text="{Binding lblName}"></TextBlock>
                                <TextBlock Text="{Binding lblKey}" Visibility="Visible"></TextBlock>
                            </StackPanel>
                       
                        
                    </DataTemplate>
                </local:MyListView.ItemTemplate>
            </local:MyListView>
            <Button x:Name="BTNTest" Content="Test" Margin="10" HorizontalAlignment="Left" Tapped="BTNTest_Tapped"></Button>
        </StackPanel>
    </Grid>

code-behind:

 public sealed partial class MainPage : Page
    {
        public List<statLabelName> stlList { get; set; }
        public MainPage()
        {
            this.InitializeComponent();
          
           
        }

        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            stlList = new List<statLabelName>();
            stlList.Add(new statLabelName { lblKey = "Key1", lblName = "Label 1", selectDefault = false });
            stlList.Add(new statLabelName { lblKey = "Key2", lblName = "Label 2", selectDefault = true });
            stlList.Add(new statLabelName { lblKey = "Key3", lblName = "Label 3", selectDefault = false });
            stlList.Add(new statLabelName { lblKey = "Key4", lblName = "Label 4", selectDefault = true });
            stlList.Add(new statLabelName { lblKey = "Key5", lblName = "Label 5", selectDefault = true });

            LVStatChoices.ItemsSource = stlList;

        }

        private void BTNTest_Tapped(object sender, TappedRoutedEventArgs e)
        {
           
            int selItems = LVStatChoices.SelectedItems.Count;
            
        }
    }

    public struct statLabelName
    {
        public string lblName { get; set; }
        public string lblKey { get; set; }
        public bool selectDefault { get; set; }
    }
    public class MyListView : ListView
    {
        protected override void PrepareContainerForItemOverride(Windows.UI.Xaml.DependencyObject element, object item)
        {
            base.PrepareContainerForItemOverride(element, item);
            // ...
            ListViewItem listItem = element as ListViewItem;
            Binding binding = new Binding();
            binding.Mode = BindingMode.TwoWay;
            binding.Source = item;
            binding.Path = new PropertyPath("selectDefault");
            listItem.SetBinding(ListViewItem.IsSelectedProperty, binding);
        }
    }

I define a MyListView which inherit from ListView class and set the ListviewItem IsSelected property to selectDefault.

Best Wishes!

---

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Click HERE to participate the survey. Thanks<br/> MSDN Community Support<br/> <br/> Please remember to &quot;Mark as Answer&quot; the responses that resolved your issue. It is a common way to recognize those who have helped you, and makes it easier for other visitors to find the resolution later.

Answer 4

Thanks Anne, it works like a charm!

After days of trying I've a solution.