ListView在启动时无法突出显示所选项目

Question

I'm currently struggling with very weird issue and cannot find the cause of it. I have a ListView :

 <ListView ItemsSource="{Binding AvailableTestCaseDatas}" Grid.Row="2" Name="GListView" SelectedItem="{Binding SelectedTestCaseData, Mode=TwoWay}">
         <ListView.Resources>
            <Style TargetType="ListViewItem">
                <Style.Resources>
                    <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="{x:Static SystemColors.HighlightColor}"/>
                </Style.Resources>
            </Style>
        </ListView.Resources>
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding TestCaseName}"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

But when it loads, I do not see the item selected, even though I'm pretty sure both bindings are correct. Furthermore, the item appears to be selected internally, but is not highlighted by ListView, because when I click on the selected item, ListView does not highlight it. When I click on the other item in the list - the clicked item is highlighted, and then I can select the item that was selected on the start.

The issue can be reproduced, even if I remove SelectedItem from XAML, and try to do listView.SelectedIndex = 0 on load event. It still does not highlight the selected item, even though it is selected and I'm pretty sure that:

1. list.Items.Contains(list.SelectedItem);
2. list.Items.Count > 0

Also when I do this:

ctor {

        listView.Loaded += ListViewLoaded;
}

    void ListViewLoaded(object sender, System.Windows.RoutedEventArgs e)
    {
        var item = listView.SelectedItem;
        listView.SelectedIndex = -1;
        listView.SelectedItem = item;
    }

Which looks extremely weird, it starts to work!

My binding:

    public TestCaseData SelectedTestCaseData
    {
        get { return _selectedTestCaseData; }
        set
        {
            _selectedTestCaseData = value;
            OnPropertyChanged("SelectedTestCaseData");
        }
    }

I tried:

1. Removing bindings, and checking the issue with the code. Still reproduced.
2. Ensured that no other references are put in the code to this list
3. Making the list enabled (it is disabled from the start)
4. Ensured that list.Items.Contains(list.SelectedItem) && list.Items.Count > 0
5. Removing style and datatemplate.

It works if I put this Loaded event, but it is a hack, and I would like at least a reason for why it behaves like that. Any tips?

Answer 1

I tried your Xaml code with some data and works fine, so the problem is in the way you are setting the property the first. The most probably issue is that the SelectedItem is been selected and unselected in the first time, something odd is happening there. I suggest you to show the code when you set the selected item (your SelectedTestCaseData ) and also the code when set the data context and when you are loading the collection data. Here I will show my code that works, maybe it helps:

Same abouve XAML but with my variables:

        <ListView ItemsSource="{Binding Persons}" Grid.Row="2" Name="GListView" SelectedItem="{Binding SelectedPerson, Mode=TwoWay}">
            <ListView.Resources>
                <Style TargetType="ListViewItem">
                    <Style.Resources>
                        <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="{x:Static SystemColors.HighlightColor}"/>
                    </Style.Resources>
                </Style>
            </ListView.Resources>
            <ListView.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Name}"/>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>

The model:

public class PersonViewModel : ViewModelBase
{
    #region Name

    private string _Name;
    private const string NameName = "Name";

    public string Name
    {
        get { return _Name; }
        set
        {
            Set(NameName, ref _Name, value);
        }
    }

    #endregion
}

The properties in the MainViewModel datacontext:

    #region Persons

    private ObservableCollection<PersonViewModel> _Persons;

    public ObservableCollection<PersonViewModel> Persons
    {
        get { return _Persons ?? (_Persons = GetAllPersons()); }
    }

    private ObservableCollection<PersonViewModel> GetAllPersons()
    {
        var toRet = new ObservableCollection<PersonViewModel>();

        foreach (var i in Enumerable.Range(1,10))
        {
            toRet.Add(new PersonViewModel {Name = string.Format("Person Name {0}", i)});
        }

        //!!!!!!!!!!!!!!!!!!!!!HERE I SET THE SELECTED ITEM
        SelectedPerson = toRet.First();

        return toRet;
    }


    #endregion

    #region SelectedPerson

    private PersonViewModel _SelectedPerson;
    private const string SelectedPersonName = "SelectedPerson";

    public PersonViewModel SelectedPerson
    {
        get { return _SelectedPerson; }
        set
        {
            Set(SelectedPersonName, ref _SelectedPerson, value);
        }
    }

    #endregion

The way the data context is set

<Window x:Class="..."
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    ...
    DataContext="{Binding Main, Source={StaticResource Locator}}">

In this case I'm user the Mvvm ligth's Locator for setting the window's data context. Hope this helps to solve this issue...