使用基础数据中不存在的结构中的项目填充 WPF TreeView

Question

我有一个不同类型的对象列表，我想在 WPF TreeView 中显示这些对象。有些对象应该是其他对象的子对象，但我不希望父对象必须维护自己的子对象列表。我试图通过为该组中的子项实现属性和 returns IEnumerator 并将其绑定为 ItemsSource 来实现此目的，但它似乎不起作用。我创建了以下内容来演示问题。

CS:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private Items MyItems;
        private int NextGroupId = 0;
        public MainWindow()
        {
            InitializeComponent();
            MyItems = new Items();
            tvMain.ItemsSource = MyItems.ItemList;
        }
        private void btnNewGroup_Click(object sender, RoutedEventArgs e)
        {
            MyItems.Add(new ItemGroup(MyItems)
            {
                Name = Guid.NewGuid().ToString(),
                GroupId = NextGroupId
            });
            NextGroupId++;
        }
        private void btnNewSubItem_Click(object sender, RoutedEventArgs e)
        {
            MyItems.Add(new SubItem(MyItems)
            {
                Name = Guid.NewGuid().ToString(),
                GroupId = (tvMain.SelectedItem as ItemGroup).GroupId
            });
        }

        private void tvMain_SelectedItemChanged(object sender,
            RoutedPropertyChangedEventArgs<object> e)
        {
            btnNewSubItem.IsEnabled = tvMain.SelectedItem is ItemGroup;
        }
    }
    public class Items
    {
        private ObservableCollection<BaseItem> _ItemList;
        public ObservableCollection<BaseItem> ItemList { get { return _ItemList; } }
        public Items()
        {
            _ItemList = new ObservableCollection<BaseItem>();
        }
        public void Add(BaseItem I)
        {
            _ItemList.Add(I);
        }
    }
    public class BaseItem
    {
        protected Items _List;
        public BaseItem(Items List)
        {
            _List = List;
        }
        public string Name { get; set; }
        public int GroupId { get; set; }
    }
    public class ItemGroup : BaseItem
    {
        public ItemGroup(Items _List)
            : base(_List) { }
        public IEnumerator Children
        {
            get
            {
                return _List.ItemList
                    .OfType<SubItem>()
                    .Where(SI => SI.GroupId == this.GroupId)
                    .GetEnumerator();
            }
        }
    }
    public class SubItem : BaseItem
    {
        public SubItem(Items _List)
            : base(_List) { }
    }
}

XAML:

<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:self="clr-namespace:WpfApplication3"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TreeView x:Name="tvMain" HorizontalAlignment="Left" Height="273" Margin="50,25,0,0" 
                  VerticalAlignment="Top" Width="265" 
                  SelectedItemChanged="tvMain_SelectedItemChanged">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type self:ItemGroup}" 
                                          ItemsSource="{Binding Children}">
                    <TextBlock Text="{Binding Name}"/>
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type self:SubItem}">
                    <TextBlock Text="{Binding Name}"/>
                </DataTemplate>
            </TreeView.Resources>
        </TreeView>
        <Button x:Name="btnNewGroup" Content="New Group" HorizontalAlignment="Left" 
                VerticalAlignment="Top" Width="100" Margin="336,142,0,0" 
                Click="btnNewGroup_Click"/>
        <Button x:Name="btnNewSubItem" Content="New SubItem" HorizontalAlignment="Left" 
                Margin="336,185,0,0" VerticalAlignment="Top" Width="100" 
                Click="btnNewSubItem_Click" IsEnabled="False"/>
    </Grid>
</Window>

明确地说，我希望 SubItems 显示为具有相同 GroupId 的 ItemGroup 的子项。请问最好的方法是什么？

Answer 1

您必须对代码进行一些重大更改：

首先，Items.ItemList 应该只包含 ItemGroup 类型的元素。现在它还包含 SubItem 类型的元素，并且它们作为父项显示在树视图中。这不是我们想要达到的。
但是，为了跟踪所有项目，我们需要另一个集合 Items.AllItems。
ItemGroup.Children 属性应修改为使用 Items.AllItems 集合而不是 Items.ItemList.
最后，我们需要在创建新子项时通知树视图。我们将使用 INotifyPropertyChanged 来这样做。

这是一个工作代码。但是，请注意，它不是生产代码。我只改变了绝对必要的东西。它的目的只是向您展示一个想法。

您还应该知道，与父对象有自己的子对象列表的方法相比，这种解决方案可能会更慢。这将取决于树视图中的项目数。

public class Items
{
    public List<BaseItem> AllItems { get; private set; }
    public ObservableCollection<BaseItem> ItemList { get; private set; }

    public Items()
    {
        ItemList = new ObservableCollection<BaseItem>();
        AllItems = new List<BaseItem>();
    }

    public void Add(BaseItem item)
    {
        AllItems.Add(item);

        if (item is ItemGroup)
            ItemList.Add(item);
        else
            AllItems.OfType<ItemGroup>().Single(i => i.GroupId == item.GroupId).Notify();
        }
    }

public class ItemGroup : BaseItem, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public ItemGroup(Items _List): base(_List) { }

    public IEnumerator Children
    {
        get
        {
            return _List.AllItems
                .OfType<SubItem>()
                .Where(SI => SI.GroupId == this.GroupId)
                .GetEnumerator();
        }
    }

    public void Notify()
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(nameof(Children)));
    }
}

Answer 2

我将接受 Michal 的回答，因为它向我展示了我做错了什么以及如何解决它。不过，我实际上找到了一个我更喜欢的不同解决方案，因为它不需要额外的收集：

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Data;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private Items MyItems;
        private int NextGroupId = 0;
        public MainWindow()
        {
            InitializeComponent();
            MyItems = new Items();
            tvMain.ItemsSource = MyItems.Groups as IEnumerable;
        }
        private void btnNewGroup_Click(object sender, RoutedEventArgs e)
        {
            MyItems.Add(new ItemGroup(MyItems)
            {
                Name = Guid.NewGuid().ToString(),
                GroupId = NextGroupId
            });
            NextGroupId++;
        }
        private void btnNewSubItem_Click(object sender, RoutedEventArgs e)
        {
            MyItems.Add(new SubItem(MyItems)
            {
                Name = Guid.NewGuid().ToString(),
                GroupId = (tvMain.SelectedItem as ItemGroup).GroupId
            });
        }

        private void tvMain_SelectedItemChanged(object sender,
            RoutedPropertyChangedEventArgs<object> e)
        {
            btnNewSubItem.IsEnabled = tvMain.SelectedItem is ItemGroup;
        }
    }
    public class Items
    {
        public ObservableCollection<BaseItem> ItemList { get; private set; }
        public ICollectionView Groups { get; private set; }
        public Items()
        {
            ItemList = new ObservableCollection<BaseItem>();
            Groups = CollectionViewSource.GetDefaultView(ItemList);
            Groups.Filter = item => item is ItemGroup;
        }
        public void Add(BaseItem item)
        {
            ItemList.Add(item);
            if (item is SubItem)
                ItemList
                    .OfType<ItemGroup>()
                    .Where(g => g.GroupId == item.GroupId)
                    .Single()
                    .NotifyPropertyChanged("Children");
        }
    }
    public class BaseItem : INotifyPropertyChanged
    {
        protected Items _List;
        public BaseItem(Items List)
        {
            _List = List;
        }
        public string Name { get; set; }
        public int GroupId { get; set; }
        public event PropertyChangedEventHandler PropertyChanged;
        public void NotifyPropertyChanged(string propName)
        {
            if (this.PropertyChanged != null)
                this.PropertyChanged(this, new PropertyChangedEventArgs(propName));
        }
    }
    public class ItemGroup : BaseItem
    {
        public ItemGroup(Items _List)
            : base(_List) { }
        public IEnumerator Children
        {
            get
            {
                return _List.ItemList
                    .OfType<SubItem>()
                    .Where(SI => SI.GroupId == this.GroupId)
                    .GetEnumerator();
            }
        }
    }
    public class SubItem : BaseItem
    {
        public SubItem(Items _List)
            : base(_List) { }
    }
}

使用基础数据中不存在的结构中的项目填充 WPF TreeView

Populate WPF TreeView with items in a structure that is not present in underlying data

c#

wpf

treeview

xaml