wpf 使用 LinQ 过滤 ObservableCollection
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Using LinQ to filter ObservableCollection
提问by Dracke
I have a MVVM application and I am trying to make filtering through LinQ work on my ObservableCollection that is gotten from database based on Entity Framework.
我有一个 MVVM 应用程序，我试图通过 LinQ 对我的 ObservableCollection 进行过滤，该集合是从基于实体框架的数据库中获取的。
In View Model I have this:
在视图模型中，我有这个：
public class MenuListViewModel : BaseViewModelCollection<Menu>
{
private string filterString;
public string FilterString
{
get { return filterString; }
set
{
if (Equals(value, filterString)) return;
filterString = value;
RaisePropertyChanged();
}
}
//TODO problems with notification, filter doesn't work
public ObservableCollection<Menu> FilteredItems
{
get
{
if (filterString == null) return Items; //Items is Observable Collection that contains every Item
var query = Items.Where(x => x.Time.ToString().StartsWith(filterString));
return new ObservableCollection<Menu>(query);
}
}
public MenuListViewModel(MenuService menuService)
{
base.Service = menuService; //Using IoC to get service
}
}
In Xaml I have the following Binding:
在 Xaml 中，我有以下绑定：
<TextBox x:Name="RecipeFilterBox" Margin="5,5,0,0" TextWrapping="Wrap" Text="{Binding FilterString, NotifyOnTargetUpdated=True}" Grid.Column="1" Height="47.07" VerticalAlignment="Top"/>
The thing is that when I write anything in the TextBox, nothing changes. I know that there is something wrong with the propertyChanged event, but I really can't figure out how to fix this. If you need any more information about this app, just ask me.
问题是当我在 TextBox 中写任何东西时，没有任何变化。我知道 propertyChanged 事件有问题，但我真的不知道如何解决这个问题。如果您需要有关此应用程序的更多信息，请询问我。
EDIT: The xaml for FilteredItems looks like this:
编辑： FilteredItems 的 xaml 如下所示：
<ListBox x:Name="MenuItemsListView" ItemsSource="{Binding FilteredItems}" SelectedItem="{Binding DeletedItem, Mode=OneWayToSource}" Foreground="#FFFFEDD3" FontFamily="Segoe Print" FontWeight="Bold" FontSize="18.667" Grid.ColumnSpan="3" Grid.Row="1" ItemContainerStyle="{DynamicResource ListBoxItemStyle1}" Style="{DynamicResource ListBoxStyle1}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Recipe.Name}" Width="255"/>
<TextBlock Width="175" Text="{Binding Time, Converter={StaticResource EnumTimeToItsDescriptionValueConverter}, Mode=OneWay}" />
<TextBlock Text="{Binding Date, StringFormat=dd.MM.yyyy}"/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
回答by Omri Btian
you can achieve this using ICollectionView.
您可以使用ICollectionView.
use FilteredItemsas the underlying source of the ICollectionViewand expose ICollectionViewto your view instead of ObservableCollection<Menu>
使用FilteredItems如的底层源ICollectionView和揭露ICollectionView你的看法，而不是ObservableCollection<Menu>
Use the filter delegate to provide the filter logic
使用过滤器委托提供过滤器逻辑
FilteredItems.Filter = item =>
{
Menu m = item as Menu;
return m.Time.ToString().StartsWith(FilterString);
}
and when FilterStringchanges invoke FilterItems.Refresh();
当FilterString更改调用时FilterItems.Refresh();
Here is an example:
下面是一个例子：
public class MenuListViewModel : BaseViewModelCollection<Menu>
{
public MenuListViewModel()
{
var data = new List<Menu> { some data ... }; // your real list of menus
// initialize the collection view
FilteredItems = CollectionViewSource.GetDefaultView(data);
// apply filtering delegate
FilteredItems.Filter = i =>
{
// This will be invoked for every item in the underlying collection
// every time Refresh is invoked
if (string.IsNullOrEmpty(FilterString)) return true;
Menu m = i as Menu;
return m.Time.ToString().StartsWith(FilterString);
};
}
private string filterString;
public string FilterString
{
get { return filterString; }
set
{
if (Equals(value, filterString)) return;
filterString = value;
FilteredItems.Refresh(); // tirggers filtering logic
RaisePropertyChanged("FilterString");
}
}
public ICollectionView FilteredItems { get; set; }
}
You would also have to change the UpdateSourceTriggeron your filter TextBoxto make it update the FilterStringevery time the user changes the text.
您还必须更改UpdateSourceTrigger过滤器上的 ，TextBox以使其在FilterString每次用户更改文本时更新。
Text="{Binding FilterString, UpdateSourceTrigger=PropertyChanged, ...}
回答by fex
Add RaisePropertyChanged("FilteredItems")inside FilterStringsetter. FilteredItemsproperty changed is never raised so bindings doesn't work the way you expect.
添加RaisePropertyChanged("FilteredItems")内部FilterString二传手。FilteredItems从未引发更改的属性，因此绑定不会按您期望的方式工作。
