Question

所以我一直在努力让我的TreeViews在很长一段时间内正常更新，所以我问是否有人能告诉我为什么我的代码没有在添加或减少时正确更新我的TreeView节点。我提前为有些大规模的代码转储道歉，但我觉得解释这个问题非常重要。

首先是我的ObservableObject类

public abstract class ObservableObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

TreeNodeBase类

public abstract class TreeNodeBase : ObservableObject
{
    protected const string ChildNodesPropertyName = "ChildNodes";

    protected string name;

    public string Name
    {
        get
        {
            return this.name;
        }

        set
        {
            this.name = value;
            this.OnPropertyChanged();
        }
    }

    protected IList<TreeNode> childNodes;

    protected TreeNodeBase(string name)
    {
        this.Name = name;
        this.childNodes = new List<TreeNode>();
    }

    public IEnumerable<TreeNode> ChildNodes
    {
        get
        {
            return this.childNodes;
        }
    }

    public TreeNodeBase AddChildNode(string name)
    {
        var treeNode = new TreeNode(this, name);
        this.childNodes.Add(treeNode);
        this.OnPropertyChanged(ChildNodesPropertyName);

        return treeNode;
    }

    public TreeNode RemoveChildNode(string name)
    {
        var nodeToRemove = this.childNodes.FirstOrDefault(node => node.Name.Equals(name));

        if (nodeToRemove != null)
        {
            this.childNodes.Remove(nodeToRemove);
            this.OnPropertyChanged(ChildNodesPropertyName);
        }

        return nodeToRemove;
    }
}

public class TreeNode : TreeNodeBase
{
    public TreeNodeBase Parent { get; protected set; }

    public TreeNode(TreeNodeBase parent, string name)
        : base(name)
    {
        this.Parent = parent;
    }
}

TreeNodeRoot类

public class TreeViewRoot : TreeNodeBase
{
    public TreeViewRoot(string name)
        : base(name)
    {
    }
}

TreeNode类

public class TreeNode : TreeNodeBase
{
    public TreeNodeBase Parent { get; protected set; }

    public TreeNode(TreeNodeBase parent, string name)
        : base(name)
    {
        this.Parent = parent;
    }
}

TreeView UserControl Xaml

<UserControl x:Class="TreeViewExperiment.TreeView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:treeViewExperiment="clr-namespace:TreeViewExperiment"
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="400"
             d:DataContext="{d:DesignInstance treeViewExperiment:TreeViewmodel}">

    <UserControl.DataContext>
        <treeViewExperiment:TreeViewmodel/>
    </UserControl.DataContext>

    <Grid Background="White">
        <Grid.Resources>
            <HierarchicalDataTemplate x:Key="TreeViewHierarchicalTemplate" ItemsSource="{Binding ChildNodes}">
                <TextBlock Text="{Binding Name}"/>
            </HierarchicalDataTemplate>

            <Style TargetType="Button">
                <Setter Property="FontFamily" Value="Verdana"/>
                <Setter Property="FontWeight" Value="Bold"/>
            </Style>
        </Grid.Resources>
        <Grid.RowDefinitions>
            <RowDefinition Height="6*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <TreeView Grid.Row="0" x:Name="Tree" ItemsSource="{Binding RootLevelNodes}" ItemTemplate="{StaticResource TreeViewHierarchicalTemplate}">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="SelectedItemChanged">
                    <i:InvokeCommandAction
                        Command="{Binding SetSelectedNode}"
                        CommandParameter="{Binding SelectedItem, ElementName=Tree}"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </TreeView>

        <Grid Grid.Row="1" Height="25">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="4*"/>
                <ColumnDefinition Width="2*"/>
                <ColumnDefinition Width="2*"/>
            </Grid.ColumnDefinitions>

            <TextBox x:Name="NameTextBox" Grid.Column="0" VerticalAlignment="Center" FontFamily="Verdana"/>
            <Button Grid.Column="1" Content="Add Node" Command="{Binding AddNode}" CommandParameter="{Binding Text, ElementName=NameTextBox}" Background="Green"/>
            <Button Grid.Column="2" Content="Remove Node" Command="{Binding RemoveNode}" Background="Red"/>
        </Grid>
    </Grid>
</UserControl>

最后是TreeViewmodel

public class TreeViewmodel : ObservableObject
{
    public ICommand SetSelectedNode { get; private set; }

    public ICommand AddNode { get; private set; }

    public ICommand RemoveNode { get; private set; }

    public TreeViewmodel()
    {
        this.SetSelectedNode = new ParamaterizedDelegateCommand(
            node =>
                {
                    this.SelectedTreeNode = (TreeNodeBase)node;
                });

        this.AddNode = new ParamaterizedDelegateCommand(name => this.SelectedTreeNode.AddChildNode((string)name));

        this.RemoveNode = new DelegateCommand(
            () =>
                {
                    if (selectedTreeNode.GetType() == typeof(TreeNode))
                    {
                        var parent = ((TreeNode)this.SelectedTreeNode).Parent;
                        parent.RemoveChildNode(this.SelectedTreeNode.Name);
                        this.SelectedTreeNode = parent;
                    }
                });

        var adam = new TreeViewRoot("Adam");
        var steve = adam.AddChildNode("Steve");
        steve.AddChildNode("Jack");

        this.rootLevelNodes = new List<TreeViewRoot> { adam, new TreeViewRoot("Eve") };
    }

    private TreeNodeBase selectedTreeNode;

    private readonly IList<TreeViewRoot> rootLevelNodes;

    public IEnumerable<TreeViewRoot> RootLevelNodes
    {
        get
        {
            return this.rootLevelNodes;
        }
    }

    public TreeNodeBase SelectedTreeNode
    {
        get
        {
            return this.selectedTreeNode;
        }

        set
        {
            this.selectedTreeNode = value;
            this.OnPropertyChanged();
        }
    }
}

所以我知道当我调试它时添加子元素时应该通知UI。我可以看到在两种情况下都调用了ChildNodes属性上的get访问器，但UI上显示的内容保持不变

过去我已经解决了这个问题，但是使用了ObservableCollections，而这似乎就是这种问题的大多数解决方案都指向StackOverflow，但为什么这个解决方案也不起作用呢？我错过了什么？

Answer 1

问题在于您滥用INotifyPropertyChanged。在您的代码中，您通知视图您的媒体资源ChildNodes已更改，但由于TreeViewItem.ItemsSource仍然等于您的ChildNodes媒体资源，因此情况并非如此。

当您查看模型更改中的基础集合对象时，

INotifyPropertyChanged将导致UI更新。

要在收集中的新项目发生时更新ItemsSource，您需要使用实现INotifyCollectionChanged的集合。

作为MSDN says：

您可以枚举任何实现IEnumerable接口的集合。但是，要设置动态绑定以便集合中的插入或删除自动更新UI，集合必须实现INotifyCollectionChanged接口。此接口公开了一个事件，只要底层集合发生更改，就应该引发该事件。

这就是为什么SO上的每个人都建议使用ObservableCollection。

编辑：

如果您想公开只读集合，请检查ReadOnlyObservableCollection<T> Class。它可以作为ObservableCollection的包装器，可以不公开。

使用HierarchicalDataTemplate的WPF MVVM TreeView不更新

1 个答案: