CollectionViewSource，如何过​​滤数据? [英] CollectionViewSource, how to filter data?

问题描述

我正在将 ComboBox 绑定到实体，但我想要过滤数据.

I am binding a ComboBox to Entities but I want the data filtered.

到目前为止，我尝试了两种方法:

Up to now I have tried two ways:

• 简单"一:通过过滤器直接应用到ObjectSetLINQ 到实体
• 如上所述设置过滤事件处理程序msdn

我对第一种方法感到满意，最重要的是因为生成到数据库的查询包含一个 WHERE 子句，因此不必从远程数据库中检索所有数据....

I am satisfied by the first approach, above all because the query generated to the database contains a WHERE clause, so not all the whole data have to be retrieved from the remote db....

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，但出现异常，为什么?

However, the #2 approach is by far more flexible, if at runtime i'd like to change the filtering applied... I have followed the example on msdn, but I get an exception, why?

所以，我的问题是:
1. 哪种方法更好
2. 为什么会出现异常?

So, my questions are:
1. Which approach is better
2. Why I get the exception?

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:我尝试在视图上实现过滤器属性而不是设置事件处理程序:

EDIT: I have tried implementing the Filter property on the View rather than setting the 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的异常:

System.NotSupportedException:不支持指定的方法.在 System.Windows.Data.CollectionView.set_Filter(Predicate`1 值)

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 绑定中，而不是在代码背后......

推荐答案

最后我找到了一个解决方案，同样发布了 在这个问题中显式声明集合的类型:

Al last I have found a solution, as posted also in this question to explicitly declare the type of the Collection:

CollectionViewType="ListCollectionView"

所以在 XAML 中添加了 Collection 类型:

So in XAML added the Collection type:

<CollectionViewSource x:Key="tSCHEDEViewSource" d:DesignSource="{d:DesignInstance my:TSCHEDE,  CreateList=True}" CollectionViewType="ListCollectionView">
    </CollectionViewSource>

现在在代码中事件处理程序起作用了:

And in code now the Event Handler works:

myCollectionViewSource.Filter += new FilterEventHandler(filterSource);

唯一的遗憾是我不明白为什么，对于看起来如此简单的事情，我必须在 XAML 中手动"强制它???对我来说，这似乎是一种黑客行为，而且很容易出错......

The only regret is that I did not understand why, for something apparently so simple, I have to force it "by hand" in XAML ??? To me this seems like an hack, and also very error prone...

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