如何从ListView绑定组合框的SelectedItem / Value / ValuePath

Question

I have a ComboBox inside of a ListView 's GridView . I am unable to get the ItemsSource and SelectedItem/Value/ValuePath bindings correct. Below is the smallest complete example demonstrating my problem:

Test_ComboBox_Binding.Views:

<Window x:Class="Test_ComboBox_Binding.Views.UserView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:system="clr-namespace:System;assembly=mscorlib"
        xmlns:m="clr-namespace:Test_ComboBox_Binding.Models"
        xmlns:vm="clr-namespace:Test_ComboBox_Binding.ViewModels"
        xmlns:s="clr-namespace:Test_ComboBox_Binding.Shared"
        Title="UserView" Height="300" Width="300">

    <Window.DataContext>
        <vm:UserViewModel/>
    </Window.DataContext>

    <Window.Resources>
        <DataTemplate x:Key="NameCellTemplate" DataType="m:cUser">
            <TextBlock Text="{Binding Name}"></TextBlock>
        </DataTemplate>       
        <DataTemplate x:Key="FavoriteColorCellTemplate" DataType="m:cUser">
            <ComboBox ItemsSource="{Binding Colors, RelativeSource={RelativeSource AncestorType=vm:UserViewModel}}"
                      SelectedValue="{Binding FavoriteColor}"
                      SelectedValuePath="{Binding FavoriteColor}"
                      MinWidth="60"/>
        </DataTemplate>        
    </Window.Resources>

    <Grid>
        <ListView ItemsSource="{Binding Users}">
            <ListView.View>
                <GridView>
                    <GridViewColumn Header="Name" Width="100" CellTemplate="{StaticResource NameCellTemplate}"></GridViewColumn>
                    <GridViewColumn Header="Favorite Color" Width="100" CellTemplate="{StaticResource FavoriteColorCellTemplate}"></GridViewColumn>
                </GridView>
            </ListView.View>
        </ListView>    
    </Grid>
</Window>

Test_ComboBoxBinding.ViewModels:

using System.Collections.Generic;
using System.Collections.ObjectModel;
using Test_ComboBox_Binding.Models;
using Test_ComboBox_Binding.Shared;

namespace Test_ComboBox_Binding.ViewModels
{
    class UserViewModel : cINotifyPropertyChangedBase
    {
        private ObservableCollection<ColorEnum> _colors;
        public ObservableCollection<ColorEnum> Colors
        {
            get { return _colors; }
            set { _colors = value; OnPropertyChanged("Colors"); }
        }

        private ObservableCollection<cUser> _users;
        public ObservableCollection<cUser> Users
        {
            get { return _users; }
            set { _users = value; OnPropertyChanged("Users");}
        }

        public UserViewModel()
        {
            Colors = new ObservableCollection<ColorEnum>(){ColorEnum.Red, ColorEnum.White, ColorEnum.Blue};

            List<cUser> userList = new List<cUser>();
            userList.Add(new cUser("Jack", Colors[0]));
            userList.Add(new cUser("Jill", Colors[1]));
            userList.Add(new cUser("James", Colors[2]));
            Users = new ObservableCollection<cUser>(userList);
        }
    }
}

Test_ComboBox_Binding.Models:

using System.ComponentModel;
using Test_ComboBox_Binding.Shared;
using Test_ComboBox_Binding.ViewModels;

namespace Test_ComboBox_Binding.Models
{
    class cUser : cINotifyPropertyChangedBase
    {
        private string _name;
        public string Name
        {
            get { return _name; }
            set { _name = value; OnPropertyChanged("Name"); }
        }

        private ColorEnum _favoriteColor;
        public ColorEnum FavoriteColor
        {
            get { return _favoriteColor; }
            set { _favoriteColor = value; OnPropertyChanged("FavoriteColor"); }
        }

        public cUser(string name, ColorEnum favoriteColor)
        {
            Name = name;
            FavoriteColor = favoriteColor;
        }
    }
}

Test_ComboBox_Binding.Shared:

namespace Test_ComboBox_Binding.Shared
{
    public enum ColorEnum
    {
        Red,
        White,
        Blue
    }
}

Running the above code will produce the image below - a ListView with a ComboBox that contains the enumerated ItemsSource correctly, yet not displaying the SelectedValue for each cUser :

Please educate me on how to get the ItemsSource and SelectedItem/Value/ValuePath set correctly. I have scoured the interweb for informations and am unable to solve this problem. I must be missing some key understanding. Thank you!

Answer 1

I believe your problem is you're setting FavoriteColor to a different referenced object than the one produced by the dataprovider binding. Try exposing a collection of Enums in the UserViewModel, binding your combobox to that collection (you may need to use FindAncestor to access it), and then using a reference from that collection to set favorite color initially.

Answer 2

The AncestorType of a RelativeSource refers to the type of element in the visual tree. You could set it to ListBox and then bind to the Colors property of the DataContext of the ListBox , which is your view model.

You should also bind the SelectedItem property to the FavoriteColor source property. This should work:

<DataTemplate x:Key="FavoriteColorCellTemplate" DataType="m:cUser">
    <ComboBox ItemsSource="{Binding DataContext.Colors, RelativeSource={RelativeSource AncestorType=ListBox}}"
              SelectedItem="{Binding FavoriteColor}"
              MinWidth="60"/>
</DataTemplate>