c# - CollectionViewSource，如何过​​滤数据？

Question

我正在将 ComboBox 绑定(bind)到实体，但我想过滤数据。

到目前为止我尝试了两种方式:

• “简单”一:直接将过滤器应用到 ObjectSet throughtLINQ 到实体
• 按照上文所述设置过滤事件处理程序 msdn

我对第一种方法很满意，最重要的是因为对数据库生成的查询包含一个 WHERE 子句，所以不必从远程数据库检索所有数据....

但是，#2 方法要灵活得多，如果在运行时我想更改应用的过滤...我已经按照 msdn 上的示例进行操作，但我得到了一个异常，为什么？

所以，我的问题是:
1. 哪种方式更好
2. 为什么我得到异常？

这是我的代码:

 private void UserControl_Loaded(object sender, RoutedEventArgs e)
    {
        //Do not load your data at design time.
        if (!System.ComponentModel.DesignerProperties.GetIsInDesignMode(this))
        {
            //Load your data here and assign the result to the CollectionViewSource.
            System.Windows.Data.CollectionViewSource myCollectionViewSource =
                (System.Windows.Data.CollectionViewSource)
                this.Resources["tSCHEDEViewSource"];

            // If I use this I get the data filtered on startup, but is it the right mode?
            //myCollectionViewSource.Source = _context.TSCHEDE.Where(s => s.KLINEA == kLinea && s.FCANC == "T").OrderBy(s => s.DSCHEDA).OrderByDescending(s => s.DSTORICO);

            // Instead If I apply my custom filtering logic
            myCollectionViewSource.Filter += new FilterEventHandler(filterSource);

            myCollectionViewSource.Source = _context.TSCHEDE; // ... Here i get an exception: 
            // 'System.Windows.Data.BindingListCollectionView' view does not support filtering. ???
        }
    }


    private void filterSource(object sender, FilterEventArgs e)
    {
        TSCHEDE scheda = e.Item as TSCHEDE;
        if (scheda != null)
        {
            if (scheda.KLINEA == 990)
            {
                e.Accepted = true;
            }
            else
            {
                e.Accepted = false;
            }
        }
    }

编辑:我尝试在 View 上实现 Filter 属性，而不是设置 EventHandler:

myCollectionView = (BindingListCollectionView)myCollectionViewSource.View;
myCollectionView.Filter = new Predicate<object>(Contains);

public bool Contains(object de)
    {
        TSCHEDE scheda = de as TSCHEDE;
        return (scheda.KLINEA == 990);
    }

现在我得到了不太有用异常:

System.NotSupportedException: Specified method is not supported. at System.Windows.Data.CollectionView.set_Filter(Predicate`1 value)

编辑

XAML 代码:

<UserControl.Resources>
    <CollectionViewSource x:Key="tSCHEDEViewSource" d:DesignSource="{d:DesignInstance my:TSCHEDE, CreateList=True}"  >
    </CollectionViewSource>
    <DataTemplate x:Key="SchedaTemplate">
        <StackPanel Orientation="Horizontal" >
            <TextBlock Text="{Binding Path=KSCHEDA}" Width="60"></TextBlock>
            <TextBlock Text="{Binding Path=DArticolo}" Width="200"></TextBlock>
            <TextBlock Text=" - " Width="40"></TextBlock>
            <TextBlock Text="{Binding Path=DSTORICO}" Width="150"></TextBlock>
        </StackPanel>
    </DataTemplate>
</UserControl.Resources>
<Grid Background="PapayaWhip" DataContext="{StaticResource tSCHEDEViewSource}" DataContextChanged="StartHere" Name="rootGrid">
    <ComboBox ItemTemplate="{StaticResource SchedaTemplate}" Grid.Column="1" Grid.Row="1" Height="23" HorizontalAlignment="Left" ItemsSource="{Binding}" Margin="23,129,0,0" Name="tSCHEDEComboBox1" SelectedValuePath="KSCHEDA" VerticalAlignment="Top" Width="393">
        <ComboBox.ItemsPanel>
            <ItemsPanelTemplate>
                <VirtualizingStackPanel />
            </ItemsPanelTemplate>
        </ComboBox.ItemsPanel>
    </ComboBox>
</Grid>

现在我认为问题出在 XAML 绑定(bind)中，而不是代码隐藏...

Answer 1

检查这个

1) CollectionView Filtering

过滤需要一个委托(delegate)(谓词)，过滤将基于该委托(delegate)(谓词)发生。 Predicate 根据它返回的值 true 或 false 接受项目，它选择或取消选择一个元素。

this.Source.Filter = item => {
    ViewItem vitem = item as ViewItem;
    return vItem != null && vitem.Name.Contains("A");
};

2) FIltering the data Dynamically