c# - 带有 ICollectionView SortDescription 的数据网格丢失了 - 错误？

Question

这就是我想要的:如果我将 ICollectionview 绑定(bind)到 DataGrid，我不想在我的 Viewmodel 中丢失 SortDescription。

我创建了一个小示例项目来了解我的意思。在我的项目中，我只是使用 Usercontrol 在 DataGrid 中显示我的数据。如果我这样做，当用户控件卸载时，SortDescritpion 消失，因为 ItemsSource 设置为 null。如果我使用 TemplateSelector 来显示我的 UserControl，SortDescription 不会消失 并且 ItemsSource 在卸载时不会设置为 null。问题是，为什么会有这些不同的行为？这 2 种行为中的一种是错误吗？

顺便说一句。我使用 .Net 4.5.1 但安装了 4.6.1 和 system.Windows.Interactivity 4.0.0.0

主窗口.xaml

<Window x:Class="DataGridICollectionView.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:DataGridICollectionView"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525">
<Window.Resources>
    <DataTemplate DataType="{x:Type local:ViewmodelListe}">
        <local:MyViewUc/>
    </DataTemplate>
</Window.Resources>
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>

    <ToolBar Grid.Row="0">
        <Button Content="SetWorkspace MyView" Click="Button_Click"/>
        <Button Content="SetWorkspace Other" Click="Button_Click_1"/>
    </ToolBar>

    <ContentPresenter Grid.Row="1" Content="{Binding Workspace}"/>
</Grid>
</Window>

主窗口.xaml.cs

namespace DataGridICollectionView
{
/// <summary>
/// Interaktionslogik für MainWindow.xaml
/// </summary>
public partial class MainWindow : Window, INotifyPropertyChanged
{
    private object _workspace;

    public MainWindow()
    {
        InitializeComponent();
        MyViewVm = new ViewmodelListe();

        DataContext = this;
    }

    public ViewmodelListe MyViewVm { get; set; }

    public object Workspace
    {
        get { return _workspace; }
        set
        {
            _workspace = value;
            OnPropertyChanged();
        }
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Workspace = MyViewVm;
    }

    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        Workspace = "Other";
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class ViewmodelListe : INotifyPropertyChanged
{
    public ViewmodelListe()
    {
        Persons = new ObservableCollection<Person>();
        MyView = CollectionViewSource.GetDefaultView(Persons);

        Persons.Add(new Person() {FirstName = "P1", LastName = "L1"});
        Persons.Add(new Person() {FirstName = "P2", LastName = "L2"});
        Persons.Add(new Person() {FirstName = "P3", LastName = "L3"});
    }

    public ObservableCollection<Person> Persons { get; private set; }

    public ICollectionView MyView { get; private set; } 

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Person : INotifyPropertyChanged
{
    private string _firstName;
    private string _lastName;

    public string FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value; 
            OnPropertyChanged();
        }
    }

    public string LastName
    {
        get { return _lastName; }
        set
        {
            _lastName = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class TestBehavior : Behavior<DataGrid>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.Unloaded += AssociatedObjectUnloaded;
    }

    private void AssociatedObjectUnloaded(object sender, RoutedEventArgs e)
    {
        //look at this in Debug Mode, its NULL if you dont use the TemplateSelector
        var itemssource = AssociatedObject.ItemsSource;


    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.Unloaded -= AssociatedObjectUnloaded;
    }
}
}

MyGridControl.xaml

<UserControl x:Class="DataGridICollectionView.MyGridControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:local="clr-namespace:DataGridICollectionView"
         xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <DataGrid ItemsSource="{Binding MyView}" AutoGenerateColumns="True">
        <i:Interaction.Behaviors>
            <local:TestBehavior/>
        </i:Interaction.Behaviors>
    </DataGrid>
</Grid>
</UserControl>

MyViewUc.xaml

<UserControl x:Class="DataGridICollectionView.MyViewUc"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:local="clr-namespace:DataGridICollectionView"
         xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
<UserControl.Resources>
    <DataTemplate x:Key="MyViewCrap">
        <local:MyGridControl/>
    </DataTemplate>

    <local:MyTemplateSelector x:Key="Selector" GridView="{StaticResource MyViewCrap}" />
</UserControl.Resources>
<Grid>
    <!--When using Contentcontrol with TemplateSelector- ItemsSource is NOT set to null -->
    <ContentControl Content="{Binding .}" ContentTemplateSelector="{StaticResource Selector}"/>
    <!--When using MyGridControl withOUT TemplateSelector- ItemsSource is set to NULL -->
    <!--<local:MyGridControl/>-->
</Grid>
</UserControl>

MyViewUc.xaml.cs

namespace DataGridICollectionView
{
/// <summary>
/// Interaktionslogik für MyViewUc.xaml
/// </summary>
public partial class MyViewUc : UserControl
{
    public MyViewUc()
    {
        InitializeComponent();
    }
}

public class MyTemplateSelector : DataTemplateSelector
{
    public DataTemplate GridView { get; set; }


    public override DataTemplate SelectTemplate(object item, System.Windows.DependencyObject container)
    {
        var chooser = item as ViewmodelListe;
        if (chooser == null)
        {
            return base.SelectTemplate(item, container);
        }

        return GridView;
    }
}
}

编辑:我最终使用了这个

public class MyDataGrid : DataGrid
{

    static MyDataGrid ()
    {
        ItemsSourceProperty.OverrideMetadata(typeof(MyDataGrid ),new FrameworkPropertyMetadata(null, OnPropertyChangedCallBack, OnCoerceItemsSourceProperty));
    }

    private ICollectionView _defaultView;
    protected override void OnItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue)
    {
        if(_defaultView != null)
            _defaultView.CollectionChanged -= LiveSortingPropertiesOnCollectionChanged;

        base.OnItemsSourceChanged(oldValue, newValue);

        _defaultView = newValue as ICollectionView;
        if(_defaultView != null)
            _defaultView.CollectionChanged += LiveSortingPropertiesOnCollectionChanged;
    }

    private void LiveSortingPropertiesOnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Reset)
        {
            foreach (var dataGridColumn in this.Columns)
            {
                var isSortDirectionSetFromCollectionView = false;
                foreach (var sortDescription in _defaultView.SortDescriptions)
                {
                    if (dataGridColumn.SortMemberPath == sortDescription.PropertyName)
                    {
                        dataGridColumn.SortDirection = sortDescription.Direction;
                        isSortDirectionSetFromCollectionView = true;
                        break;
                    }
                }

                if (!isSortDirectionSetFromCollectionView)
                {
                    dataGridColumn.SortDirection = null;
                }
            }
        }
    }

    private static void OnPropertyChangedCallBack(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var grd = d as MyDataGrid ;
        var view = e.NewValue as ICollectionView;

        if (grd == null || view == null)
            return;

        foreach (var dataGridColumn in grd.Columns)
        {
            var isSortDirectionSetFromCollectionView = false;
            foreach (var sortDescription in view.SortDescriptions)
            {
                if (dataGridColumn.SortMemberPath == sortDescription.PropertyName)
                {
                    dataGridColumn.SortDirection = sortDescription.Direction;
                    isSortDirectionSetFromCollectionView = true;
                    break;
                }
            }
            //wenn die View nicht sortiert war, auch die column nicht Sortieren
            if (!isSortDirectionSetFromCollectionView)
            {
                dataGridColumn.SortDirection = null;
            }
        }
    }


    private static object OnCoerceItemsSourceProperty(DependencyObject d, object baseValue)
    {
        // do nothing here - we just want to override parent behaviour.
        // The _only_ thing DataGrid does here is clearing sort descriptors
        return baseValue;
    }


}

Answer 1

当您直接在 MyViewUc 中托管 MyGridControl 时(案例 1)- 当您切换工作区并且卸载 MyViewUC 时，它的数据上下文设置为空。因为 MyGridControl 是直接子级 - 它的 datacontext 也设置为 null，而 DataGrid 的 DataContext 又设置为 null。这也将 ItemsSource 设置为 null，因为它绑定(bind)到 DataContext。您可以通过查看行为中 DataGrid 的 DataContext 来验证这一点。这种行为在我看来是完全合理的。

当您使用模板选择器时:MyViewUC 被卸载，它的数据上下文被设置为空。然后 ContentControl Content 也设置为 null。现在的问题是:当您使用 ContentTemplateSelector 时，旧的(未加载的)MyGridControl 的 DataContext 未设置为 null。您可以在您的行为中验证这一点，这就是保留 ItemsSource 和排序描述符的原因。

现在，我认为第二个行为是不正确的，对于这个由 ContentTemplateSelector 创建的未加载控件，应该将 datacontext 设置为 null。这背后的逻辑不是很简单 - 您可以自己查看 ContentPresenter.OnContentChanged 方法的源代码，您将在其中看到内容更改时 DataContext 何时未更新。

更新:我看到您主要关心的是丢失排序描述符，但这是丢失 DataContext 并将 ItemsSource 设置为 null 的直接后果。对我来说，这种行为看起来很合理，但我确实看到很多人并非如此，因此甚至有关于此问题的错误报告:https://connect.microsoft.com/VisualStudio/feedback/details/592897/collectionviewsource-sorting-only-the-first-time-it-is-bound-to-a-source

您可以在 DataGrid 源代码中看到自己:

protected override void OnItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue)
{
  base.OnItemsSourceChanged(oldValue, newValue);
  if (newValue == null)
    this.ClearSortDescriptionsOnItemsSourceChange();
  // more code here....
}

因此，当您将 ItemsSource 设置为 null 时 - 所有排序描述符都会被明确清除。在上面的链接中，您可以找到一些您可能会觉得有用的解决方法。

更新 2:您可以考虑尝试通过继承 DataGrid 来修复该行为。我并不是说这是完美的解决方案，但使用 ContentTemplateSelector 也不是。当 ItemsSource 设置为 null 时，有两个地方会清除排序描述符 - 在 OnItemsSourceChanged 和 OnCoerceItemsSourceProperty 中。因此，您可以执行以下操作:

public class MyDataGrid : DataGrid {
    static MyDataGrid() {
        ItemsSourceProperty.OverrideMetadata(typeof(MyDataGrid), new FrameworkPropertyMetadata(null, OnCoerceItemsSourceProperty));
    }

    private static object OnCoerceItemsSourceProperty(DependencyObject d, object baseValue) {
        // do nothing here - we just want to override parent behaviour.
        // The _only_ thing DataGrid does here is clearing sort descriptors
        return baseValue;
    }

    protected override void OnItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue) {
        SortDescription[] sorts = null;
        if (newValue == null) {
            // preserve sort descriptors when setting ItemsSource to null
            sorts = Items.SortDescriptions.ToArray();
        }
        // they will now be cleared here
        base.OnItemsSourceChanged(oldValue, newValue);            
        if (sorts != null) {
            // restore them back
            foreach (var sort in sorts) {
                Items.SortDescriptions.Add(sort);
            }
        }
    }
}

通过上面的代码，您将看到在切换数据上下文之间，排序描述符保留在您的 MyView 中。