C#中将Dictionary绑定到ComboBox的问题

原代码片段 #

XML文件内容 #

<configuration>
    <Paths>
        <add key="Path_DQM_CE_Prod" value="DQM-CE\DQM_CE_12.2.0_17615\QMConfigurationEditor.exe" />
        <add key="Path_DQM_CE_Test" value="DQM-CE\QMConfigurationEditor.exe" />
    </Paths>
</configuration>

后台代码 #

public MainWindow()
{
    InitializeComponent();
    this.DataContext = this;
    ///read XML and store into dictionary
    var xdoc = XDocument.Load(@"\\ServerXYZ\Settings_CAX_Startcenter\config.xml");

    var Paths = xdoc.Root.Descendants("Paths").Elements()
                       .ToDictionary(a => (string)a.Attribute("key"),
                                     a => (string)a.Attribute("value"));
}

XAML代码 #

<Grid>
    <StackPanel HorizontalAlignment="Left">
        <ComboBox ItemsSource="{Binding Paths}" DisplayMemberPath="Value.Key" />
    </StackPanel>
</Grid>

问题分析与修复方案 #

绑定失败的核心原因有两个：

1. Paths是局部变量，无法被WPF绑定系统访问
   WPF的数据绑定要求绑定目标是公共属性，而你当前的Paths是构造函数内的局部变量，绑定引擎找不到这个成员。

2. DisplayMemberPath设置错误
   Dictionary的每个元素是KeyValuePair<string, string>类型，其中Key对应XML里的key属性，Value对应XML里的value属性。你写的Value.Key是错误的，应该根据需求选择Key或Value作为显示内容。

修正后的后台代码 #

// 定义公共属性供绑定使用
public Dictionary<string, string> Paths { get; private set; }

public MainWindow()
{
    InitializeComponent();
    this.DataContext = this;
    
    var xdoc = XDocument.Load(@"\\ServerXYZ\Settings_CAX_Startcenter\config.xml");
    // 给公共属性赋值，而非局部变量
    Paths = xdoc.Root.Descendants("Paths").Elements()
                       .ToDictionary(a => (string)a.Attribute("key"),
                                     a => (string)a.Attribute("value"));
}

修正后的XAML代码 #

如果想显示XML里的key值（比如Path_DQM_CE_Prod）：

<Grid>
    <StackPanel HorizontalAlignment="Left">
        <ComboBox ItemsSource="{Binding Paths}" DisplayMemberPath="Key" />
    </StackPanel>
</Grid>

如果想显示XML里的value值（比如文件路径）：

<Grid>
    <StackPanel HorizontalAlignment="Left">
        <ComboBox ItemsSource="{Binding Paths}" DisplayMemberPath="Value" />
    </StackPanel>
</Grid>

额外优化（可选） #

如果后续需要动态更新Paths并让ComboBox自动刷新，建议实现INotifyPropertyChanged接口：

using System.ComponentModel;

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private Dictionary<string, string> _paths;
    public Dictionary<string, string> Paths
    {
        get => _paths;
        set
        {
            _paths = value;
            OnPropertyChanged(nameof(Paths));
        }
    }

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        
        var xdoc = XDocument.Load(@"\\ServerXYZ\Settings_CAX_Startcenter\config.xml");
        Paths = xdoc.Root.Descendants("Paths").Elements()
                       .ToDictionary(a => (string)a.Attribute("key"),
                                     a => (string)a.Attribute("value"));
    }
}

内容的提问来源于stack exchange，提问作者Moritz