List in dropdownbox in grid does not return value

Question

I have an enum

enum SendDays
{
    Maandag = 1,
    Dinsdag,
    Vandaag= 99
}

And a Class

public struct DayListModel
{
    public int Id;
    public string DayName;
}

I fill a list with days like this

private void Filldays()
{
   foreach(int i in Enum.getValues(typeof(SendDays)))
   {
        DayListModel day =new DaylistModel()
        {
            Id = i,
            Dayname = Enum.GetName(typeof(SendDays), i)
         };
         DayList.Add(day);
   }

When I use this is in A telerik RadGridView in a radcombobox like

<telerik:RadComboBox ItemsSource="{Bindning DayList}" DisplayMemberPath="DayName" SelectedValue="{Bindning DefaultSendDay}" SelectedValuePath="Id"/>

Whenever I change the selecteditem this is not passed.

Any suggestions?

Jeroen

`SelectedValuePath` must denote the name of a property. Your `Id` is a field. `DayListModel` should also be a class, not a struct. — Clemens, Sep 23 '20 at 14:34
DefaultSendDay is a Byte (smallint in SQL, Byte through Entity Framework) — Jeroen E, Sep 23 '20 at 14:39
The difference in types was a key flaw in the original post, Matching those solved most of it — Jeroen E, Sep 24 '20 at 07:20

score 2 · Answer 1 · answered Sep 23 '20 at 14:51

Make sure that the types matches, i.e. if your DefaultSendDay source property is a byte, the Id of the DayListModel should also be a byte.

If it still doesn't work, try to convert the fields into properties and the struct to a class:

public class DayListModel
{
    public byte Id { get; set; }
    public string DayName { get; set; }
}

score 2 · Accepted Answer · answered Sep 23 '20 at 15:49

Here is my advice, and how I got it to work:

Like @mm8 said, you should make the DayListModel a class not a struct, and turn the fields into properties. If you don't use properties, the DisplayMemberPath doesn't work. Some stuff doesn't work with structs (like using == to compare) so I would go with a class in this case.
Are your objects observable in your view model? I don't know telerik, but you should be calling some sort of PropertyChanged method so the UI can update. If you use a framework like MVVM light it has ObservableObjects and RaisePropertyChanged methods.

Here is a working example:

MainWindowVM.cs

using GalaSoft.MvvmLight;
using System;
using System.Collections.Generic;

namespace WpfApp1
{
    public class MainWindowVM : ObservableObject
    { 
        private List<DayListModel> _DayList;
        public List<DayListModel> DayList
        {
            get { return _DayList; }
            set
            {
                if (value != _DayList)
                {
                    _DayList = value;
                    RaisePropertyChanged();
                }
            }
        }


        private DayListModel _DefaultSendDay;
        public DayListModel DefaultSendDay
        {
            get { return _DefaultSendDay; }
            set
            {
                if (value != _DefaultSendDay)
                {
                    _DefaultSendDay = value;
                    RaisePropertyChanged();
                }
            }
        }

        public MainWindowVM()
        {
            DayList = new List<DayListModel>();
            foreach (int i in Enum.GetValues(typeof(SendDays)))
            {
                DayListModel day = new DayListModel()
                {
                    Id = i,
                    DayName = Enum.GetName(typeof(SendDays), i)
                };
                DayList.Add(day);
            }
            DayList = new List<DayListModel>(DayList);
        }
    }

    public enum SendDays
    {
        Maandag = 1,
        Dinsdag,
        Vandaag = 99
    }

    public class DayListModel
    {
        public int Id { get; set; }
        public string DayName { get; set; }
    }
}

MainWindow.xaml

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.DataContext>
        <local:MainWindowVM />
    </Window.DataContext>

    <Grid >
        <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
            <ComboBox  ItemsSource="{Binding DayList}" SelectedItem="{Binding DefaultSendDay}" DisplayMemberPath="DayName" >
            </ComboBox>
            <TextBlock Text="{Binding DefaultSendDay.DayName}"/>
        </StackPanel>
    </Grid>
</Window>

Screenshot:

Thanks for this example. The main issues where turning the struct into class, fields into properties and matching DefaultSendDay and Id both as Byte. I accepted your answer because it shows it all. — Jeroen E, Sep 24 '20 at 07:17
Thanks, although I didn't make the Id a byte in mine. You may want to [make the enum a byte](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/enum) explicitly. — Peter Boone, Sep 24 '20 at 15:08

List in dropdownbox in grid does not return value

2 Answers2