我有一个使用Model-View-ViewModel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View中的ListBox。
<ListBox Grid.Row="1" ItemsSource="{Binding Useragents}" SelectionMode="Multiple"/>
ListBox的SelectionMode = Multiple，因此您可以一次选择更多项目。现在，ViewModel需要知道选择了哪些项目。
问题是：在View-Model-ViewModel模式中，ViewModel无法访问View，因此我不能只询问ListBox选择了哪些项目。我只有ListCollectionView，但我找不到一种方法来找到那里选择的项目。
那么如何在ListBox中找到已选择的项目？或者实现这一目标的技巧（可能在我的项目中绑定某个布尔'IsSelected'但是什么？怎么样？）
也许有人使用这种模式也可以帮助我吗？
答案 0 :(得分：12)
您需要在其上创建一个具有IsSelected概念的ViewModel，并绑定到使用标准WPF绑定体系结构在View中表示它的实际ListBoxItem的IsSelected属性。
然后在您的代码中，它知道您的ViewModel，而不是它由任何特定View表示的事实，可以使用该属性来找出模型中的哪些项目实际被选中，而不管设计者如何选择它在视图中表示。
答案 1 :(得分：8)
PRISM MVVM Reference Implementation有一个名为SynchronizeSelectedItems的行为，在Prism4 \ MVVM RI \ MVVM.Client \ Views \ MultipleSelectionView.xaml中使用，它将已检查项与名为Selections的ViewModel属性同步：
<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/并全部抓取或使用：
//===================================================================================
// 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;
}
}
}
}
}
答案 2 :(得分：1)
答案 3 :(得分：1)
Drew Marsh的解决方案非常有效，我推荐它。我有另一个解决方案！
模型视图ViewModel是Passive View，您还可以使用Presentation Model访问演示文稿的某些数据，而无需与WPF结合使用 （此模式用于Stocktrader的PRISM示例。
答案 4 :(得分：1)
答案 5 :(得分：1)
对我来说，最好的答案是打破MVVM的原则。
关于背后的代码 1. Instanciate你的viewModel 2.添加事件处理程序SelectionChanged 3.遍历所选项目并将每个项目添加到viewModel
列表中ViewModel viewModel = new ViewModel();
viewModel.SelectedModules = new ObservableCollection<string>();
foreach (var selectedModule in listBox1.SelectedItems)
{
viewModel.SelectedModules.Add(selectedModule.ToString());
}
答案 6 :(得分：0)
以下是View-Model-ViewModel Pattern的另一种变体，其中ViewModel可以通过IView接口访问视图。
我遇到了很多不能使用WPF绑定的场景，然后你需要一种代码来同步View和ViewModel之间的状态。
如何做到这一点如下所示：
答案 7 :(得分：0)
答案 8 :(得分：0)
David Rogers的解决方案很棒，详情请参阅以下相关问题：
Sync SelectedItems in a muliselect listbox with a collection in ViewModel