WPF M-V-VM:从 ListCollectionView 中获取选定项目? [英] WPF M-V-VM: Get selected items from a ListCollectionView?
问题描述
我有一个使用模型-视图-视图模型模式的 WPF 应用程序.
在我的 ViewModel 中，我有一个 ListCollectionView 来保存项目列表.
此 ListCollectionView 绑定到我的视图中的 ListBox.
I've got a WPF app using the Model-View-ViewModel pattern.
In my ViewModel I've got a ListCollectionView to keep a list of items.
This ListCollectionView is bound to a ListBox in my View.
<ListBox Grid.Row="1" ItemsSource="{Binding Useragents}" SelectionMode="Multiple"/>
ListBox 的 SelectionMode=Multiple，因此您可以一次选择多个项目.现在 ViewModel 需要知道哪些项目已被选中.
The ListBox has SelectionMode=Multiple, so you can select more items at one time. Now the ViewModel needs to know which items has been selected.
问题是:在 View-Model-ViewModel 模式中，ViewModel 无法访问 View，所以我不能只询问 ListBox 哪些项目已被选中.我只有 ListCollectionView，但我找不到找到其中选择了哪些项目的方法.
The problem is: in the View-Model-ViewModel pattern the ViewModel has no access to the View, so I can't just ask the ListBox which items has been selected. All I have is the ListCollectionView, but I can't find a way to find which items has been selected in there.
那么我如何找到 ListBox 中哪些项目被选中了呢?或者实现这一点的技巧(可能将某些东西绑定到我的项目中的布尔IsSelected"?但是什么?如何?)
So how do I find which items has been selected in the ListBox? Or a trick to achieve this (maybe bind something to a Boolean 'IsSelected' in my items? But what? How?)
也许正在使用这种模式的人也可以在这里帮助我?
Maybe someone who is using this pattern, too, can help me here?
推荐答案
PRISM MVVM 参考实现 有一个称为 SynchronizeSelectedItems 的行为，在 Prism4MVVM RIMVVM.ClientViewsMultipleSelectionView.xaml 中使用，它将选中的项目与名为 Selections 的 ViewModel 属性同步:
PRISM MVVM Reference Implementation has a behaviour called SynchronizeSelectedItems, used in Prism4MVVM RIMVVM.ClientViewsMultipleSelectionView.xaml, which synchronizes checked items with the ViewModel property named Selections:
<ListBox Grid.Column="0" Grid.Row="1" IsTabStop="False" SelectionMode="Multiple"
ItemsSource="{Binding Question.Range}" Margin="5">
<ListBox.ItemContainerStyle>
<!-- Custom style to show the multi-selection list box as a collection of check boxes -->
<Style TargetType="ListBoxItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ListBoxItem">
<Grid Background="Transparent">
<CheckBox IsChecked="{Binding IsSelected, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"
IsHitTestVisible="False" IsTabStop="True"
AutomationProperties.AutomationId="CheckBoxAutomationId">
<ContentPresenter/>
</CheckBox>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ListBox.ItemContainerStyle>
<i:Interaction.Behaviors>
<!-- Custom behavior that synchronizes the selected items with the view models collection -->
<Behaviors:SynchronizeSelectedItems Selections="{Binding Selections}"/>
</i:Interaction.Behaviors>
</ListBox>
转到 http://compositewpf.codeplex.com/ 并全部获取或使用此:
Go to http://compositewpf.codeplex.com/ and grab it all or use this:
//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation. All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious. No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Collections;
using System.Collections.Specialized;
using System.Diagnostics.CodeAnalysis;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;
namespace MVVM.Client.Infrastructure.Behaviors
{
/// <summary>
/// Custom behavior that synchronizes the list in <see cref="ListBox.SelectedItems"/> with a collection.
/// </summary>
/// <remarks>
/// This behavior uses a weak event handler to listen for changes on the synchronized collection.
/// </remarks>
public class SynchronizeSelectedItems : Behavior<ListBox>
{
public static readonly DependencyProperty SelectionsProperty =
DependencyProperty.Register(
"Selections",
typeof(IList),
typeof(SynchronizeSelectedItems),
new PropertyMetadata(null, OnSelectionsPropertyChanged));
private bool updating;
private WeakEventHandler<SynchronizeSelectedItems, object, NotifyCollectionChangedEventArgs> currentWeakHandler;
[SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly",
Justification = "Dependency property")]
public IList Selections
{
get { return (IList)this.GetValue(SelectionsProperty); }
set { this.SetValue(SelectionsProperty, value); }
}
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.SelectionChanged += this.OnSelectedItemsChanged;
this.UpdateSelectedItems();
}
protected override void OnDetaching()
{
this.AssociatedObject.SelectionChanged += this.OnSelectedItemsChanged;
base.OnDetaching();
}
private static void OnSelectionsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var behavior = d as SynchronizeSelectedItems;
if (behavior != null)
{
if (behavior.currentWeakHandler != null)
{
behavior.currentWeakHandler.Detach();
behavior.currentWeakHandler = null;
}
if (e.NewValue != null)
{
var notifyCollectionChanged = e.NewValue as INotifyCollectionChanged;
if (notifyCollectionChanged != null)
{
behavior.currentWeakHandler =
new WeakEventHandler<SynchronizeSelectedItems, object, NotifyCollectionChangedEventArgs>(
behavior,
(instance, sender, args) => instance.OnSelectionsCollectionChanged(sender, args),
(listener) => notifyCollectionChanged.CollectionChanged -= listener.OnEvent);
notifyCollectionChanged.CollectionChanged += behavior.currentWeakHandler.OnEvent;
}
behavior.UpdateSelectedItems();
}
}
}
private void OnSelectedItemsChanged(object sender, SelectionChangedEventArgs e)
{
this.UpdateSelections(e);
}
private void UpdateSelections(SelectionChangedEventArgs e)
{
this.ExecuteIfNotUpdating(
() =>
{
if (this.Selections != null)
{
foreach (var item in e.AddedItems)
{
this.Selections.Add(item);
}
foreach (var item in e.RemovedItems)
{
this.Selections.Remove(item);
}
}
});
}
private void OnSelectionsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
this.UpdateSelectedItems();
}
private void UpdateSelectedItems()
{
this.ExecuteIfNotUpdating(
() =>
{
if (this.AssociatedObject != null)
{
this.AssociatedObject.SelectedItems.Clear();
foreach (var item in this.Selections ?? new object[0])
{
this.AssociatedObject.SelectedItems.Add(item);
}
}
});
}
private void ExecuteIfNotUpdating(Action execute)
{
if (!this.updating)
{
try
{
this.updating = true;
execute();
}
finally
{
this.updating = false;
}
}
}
}
}
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