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我刚刚开始在重新开发应用程序时探索 MV-VM 设计模式，并且我正在运行一个一致的主题，其中我有我需要我的 ViewModel 向 View 公开的集合，其中包含要选择的项目用户。请注意，当我说“已选择”时，我的意思是它们以某种永久方式被选择，例如在网格控件中使用复选框，而不像在常规列表框控件中那样突出显示。到目前为止，我对如何实现这一点有两种不同的想法，我想知道是否有关于哪种方式最好的想法。

  1. 公开两个单独的集合，一个表示可用项目的只读副本，另一个表示包含在第一个集合中的项目的子集，并表示当前选择的可用项目的那些。
  2. 通过我的 ViewModel 公开一个集合，但使该集合成为一个专门的集合，以某种方式跟踪选择了集合的哪些项目。可以在Josh Twist的这篇文章中找到这种方法的一个示例。

我确实意识到选项 2 实际上只是选项 1 的修改，除了两个集合作为一个单元进行管理。我更感兴趣的是了解哪些方法在 WPF 中的可管理性、性能和有效数据绑定方面已被证明是成功的。

我还看到一篇关于如何在 WPF 中将数据绑定到 SelectedItems 属性的文章，以及另一篇详细介绍如何将多选列表框与 ViewModel 同步的文章。在阅读了那里的不同方法之后，我意识到这可能不是 MV-VM 从业者达成的共识，但是我希望我可以在不尝试每个方法并进行比较的情况下稍微限制该领域。

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2 回答 2

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编辑

以前有 Josh Smith 的一篇文章的链接，但目前已损坏。

但是，现在我使用了NanoMVVM库中的SelectionViewModel和其他一些辅助类。

该库尚未用于生产用途，但可能有一些有用的东西，包括具有不同选择模式的 MVVM 选择的运行示例。

于 2009-08-05T21:20:27.653 回答
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PRISM MVVM 参考实现有一个称为 SynchronizeSelectedItems 的行为，在 Prism4\MVVM RI\MVVM.Client\Views\MultipleSelectionView.xaml 中使用，它将选中的项目与名为的 ViewModel 属性同步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/并全部获取或使用它：

//===================================================================================
// 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;
                }
            }
        }
    }
}
于 2011-12-03T17:36:30.873 回答