我将ComboBox绑定到实体,但我想要过滤数据。
到目前为止,我尝试了两种方法:
我对第一种方法感到满意,首先是因为生成到数据库的查询包含WHERE子句,所以不是所有的数据都必须从远程数据库中检索....
然而,#2方法更灵活,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,但我得到一个例外,为什么?
所以,我的问题是:
1.哪种方法更好
2.为什么我得到例外?
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);
}
现在我得到了不那么有用的例外:
System.NotSupportedException:不支持指定的方法。 在System.Windows.Data.CollectionView.set_Filter(Predicate`1 value)
修改
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 Binding中,而不是代码背后......
答案 0 :(得分:8)
检查
过滤需要基于过滤器发生的委托(谓词)。谓词根据它返回的值true或false接收项目,它选择或取消选择元素。
this.Source.Filter = item => {
ViewItem vitem = item as ViewItem;
return vItem != null && vitem.Name.Contains("A");
};
答案 1 :(得分:7)
最后我找到了一个解决方案,也发布了in this question 明确声明Collection的类型:
<强> CollectionViewType = “的ListCollectionView”强>
所以在XAML中添加了Collection类型:
<CollectionViewSource x:Key="tSCHEDEViewSource" d:DesignSource="{d:DesignInstance my:TSCHEDE, CreateList=True}" CollectionViewType="ListCollectionView">
</CollectionViewSource>
现在代码中的事件处理程序可以运行:
myCollectionViewSource.Filter += new FilterEventHandler(filterSource);
唯一的遗憾是我不明白为什么,因为显然这么简单,我必须在XAML中“手动”强制它??? 对我而言,这似乎是一种黑客攻击,也非常容易出错......
答案 2 :(得分:0)
<TextBox x:Name="FilterTextBox">
<b:Interaction.Triggers>
<b:EventTrigger EventName="TextChanged">
<b:CallMethodAction
MethodName="Refresh"
TargetObject="{Binding View, BindsDirectlyToSource=True, Source={StaticResource tSCHEDEViewSource}}" />
</b:EventTrigger>
</b:Interaction.Triggers>
</TextBox>