从绑定到ObservableDictionary的ComboBox上的值中获取选定字段

using System.Collections.ObjectModel;
using System.ComponentModel;

public class ViewModel : INotifyPropertyChanged
{
    private ObservableCollection<KeyValuePair<string, string>> _items;
    public ObservableCollection<KeyValuePair<string, string>> Items
    {
        get => _items;
        set
        {
            _items = value;
            OnPropertyChanged(nameof(Items));
        }
    }

    private KeyValuePair<string, string> _selectedItem;
    public KeyValuePair<string, string> SelectedItem
    {
        get => _selectedItem;
        set
        {
            _selectedItem = value;
            OnPropertyChanged(nameof(SelectedItem));
        }
    }

    public ViewModel()
    {
        Items = new ObservableCollection<KeyValuePair<string, string>>
        {
            new KeyValuePair<string, string>("1", "Option 1"),
            new KeyValuePair<string, string>("2", "Option 2"),
            new KeyValuePair<string, string>("3", "Option 3")
        };
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

<ComboBox ItemsSource="{Binding Items}"
          SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
          DisplayMemberPath="Value"
          SelectedValuePath="Key"/>

string selectedKey = viewModel.SelectedItem.Key;
string selectedValue = viewModel.SelectedItem.Value;