c# - 如何在重用之前清理 ListViewItem 的状态？

Question

问题是列表视图使用虚拟化，并且当项目改变它们的外观时，它们在列表刷新后仍然存在。这是微软工程师的回答

这是由 ListView 的默认面板 (ItemsStackPanel) 的虚拟化特性引起的。它本质上重用了相同的 ListViewItem（容器），当它重用它们时，它可能处于不正确的状态。当您使用堆栈面板时，没有虚拟化，并且每个项目都有一个容器（没有重用），您可以想象，如果列表中有很多项目，这会变得非常耗时。您可以尝试使用 PrepareContainerForItemOverride、ClearContainerForItemOverride 在重用之前清理 ListViewItem 的状态。更好的是使用 ContainerContentChanging 事件并在那里执行，这样您就不需要派生类型。

不幸的是，我找不到使用PrepareContainerForItemOverride、ClearContainerForItemOverride和ContainerContentChanging方法的示例。

如何在 ContainerContentChanging 中清除 ListViewItem 的状态？

更新：

用户控制：

<Grid>
        <SwipeControl x:Name="ListViewSwipeContainer">
            <Grid VerticalAlignment="Center">
                <Grid.RowDefinitions>
                    <RowDefinition Height="auto"/>
                    <RowDefinition Height="auto"/>
                </Grid.RowDefinitions>
                <TextBlock
                    Margin="10,5,200,5"
                    HorizontalAlignment="Left"
                    VerticalAlignment="Center"
                    FontSize="18"
                    Text="{Binding ElementName=subsceneView, Path=Title}"
                    TextWrapping="Wrap"/>
                <AppBarButton
                    Name="OpenFolderButton"
                    Grid.RowSpan="2"
                    MinWidth="75"
                    Margin="10,0,10,0"
                    HorizontalAlignment="Right"
                    VerticalAlignment="Center"
                    Click="OpenFolderButton_Click"
                    Icon="OpenLocal"
                    IsTabStop="False"
                    Label="Open Folder"
                    Visibility="Collapsed"/>

                <AppBarButton
                    Name="DownloadHoverButton"
                    Grid.RowSpan="2"
                    Margin="10,0,10,0"
                    HorizontalAlignment="Right"
                    VerticalAlignment="Center"
                    Click="DownloadHoverButton_Click"
                    Icon="Download"
                    IsTabStop="False"
                    Label="Download"
                    Visibility="Collapsed"/>

            </Grid>
        </SwipeControl>
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup x:Name="HoveringStates">
                <VisualState x:Name="HoverButtonsHidden"/>
                <VisualState x:Name="HoverButtonsShown">
                    <VisualState.Setters>
                        <Setter Target="DownloadHoverButton.Visibility" Value="Visible"/>
                    </VisualState.Setters>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>
    </Grid>

后面的代码：

public sealed partial class SubsceneUserControl : UserControl
    {
        #region DependencyProperty
       

        public static readonly DependencyProperty TitleProperty =
        DependencyProperty.Register("Title", typeof(string), typeof(SubsceneUserControl),
            new PropertyMetadata(string.Empty));

        public string Title
        {
            get { return (string)GetValue(TitleProperty); }
            set { SetValue(TitleProperty, value); }
        }

        
        #endregion
        public SubsceneUserControl()
        {
            this.InitializeComponent();
        }
        private void UserControl_PointerEntered(object sender, PointerRoutedEventArgs e)
        {
            if (e.Pointer.PointerDeviceType == Windows.Devices.Input.PointerDeviceType.Mouse ||
                e.Pointer.PointerDeviceType == Windows.Devices.Input.PointerDeviceType.Pen)
            {
                VisualStateManager.GoToState(sender as Control, "HoverButtonsShown", true);
            }
        }

        private void UserControl_PointerExited(object sender, PointerRoutedEventArgs e)
        {
            VisualStateManager.GoToState(sender as Control, "HoverButtonsHidden", true);
        }

        private void OpenFolderButton_Click(object sender, RoutedEventArgs e)
        {

        }

        private void DownloadHoverButton_Click(object sender, RoutedEventArgs e)
        {
            OpenFolderButton.Visibility = Visibility.Visible;
            DownloadHoverButton.Visibility = Visibility.Collapsed;
        }
    }

这是我的列表视图

<ListView
            x:Name="listv"
            ItemsSource="{x:Bind Subtitles, Mode=OneWay}">
            <ListView.ItemTemplate>
                <DataTemplate x:DataType="local:SubsceneDownloadModel">
                    <local:SubsceneUserControl Title="{x:Bind Title}"/>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>

private void AddItems()
        {
            Subtitles?.Clear();
            for (int i = 0; i < 10; i++)
            {
                Subtitles.Add(new SubsceneDownloadModel { Title = "Test " + i });

            }
        }

标签： c#xamllistviewuwp

Answer 1

ListViewItem 在被重用之前的状态

对于这种情况，更好的方法是使用 mvvm 绑定和实现INotifyPropertyChanged模型类。有关更多详细信息，请参阅深入的数据绑定。

例如

模型类

public class Model : INotifyPropertyChanged
{
    public Model(string name)
    {
        this.Name = name;
    }
   private string _name;

    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            _name = value;
            NotifyPropertyChanged();
        }
    }

    private bool _visible;
    public bool Visible
    {

        get => _visible;
        set
        {
            _visible = value;
            NotifyPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            // PropertyChanged is always null.
            PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

Xaml

<ListView x:Name="MyList">
    <ListView.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Name}" />
                <SymbolIcon
            x:Name="MySbl"
            HorizontalAlignment="Right"
            Symbol="Accept"
            Visibility="{Binding Visible}" />
            </StackPanel>

        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

用法

MyList.ItemsSource = new ObservableCollection<Model> {
        new Model("hello"),
          new Model("hello1"),
            new Model("hello2"),
              new Model("hello3"),
                new Model("hello4"),
                  new Model("hello5"),
                    new Model("hello6"),
        };