How to bind ItemsSource to ComboBox within a DataTemplate

Question

ItemsSource binding to a list seems to be working fine except for when inside a DataTemplate. I have 3 ComboBoxes right now: 2 which are inside a DataTemplate, where one of them has hardcoded items which are working and one which has ItemsSource set which is not working. The last is outside a DataTemplate and is working with an ItemsSource. 2 lists of ComboBoxes and 1 ComboBox

I have tried to modify the DataContext, RelativeSource, and ElementName, but without any luck.

The ItemsSource list contains ListEntry

public class ListEntry : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        private string m_name;
        private string m_desc;

        public ListEntry(string name, string desc)
        {
            Name = name;
            Desc = desc;
        }

        public string Name
        {
            get { return m_name; }
            set { m_name = value; NotifyPropertyChanged("Name"); }
        }
        public string Desc
        {
            get { return m_desc; }
            set { m_desc = value; NotifyPropertyChanged("Desc"); }
        }
    }

This is my DataContext

public class DataClass : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        private ObservableCollection<ListEntry> m_itemsList;

        public ObservableCollection<ListEntry> ItemsList
        {
            get { return m_itemsList; }
            set { m_itemsList = value; NotifyPropertyChanged("ItemsList"); }
        }

    }

This is the ComboBox with ItemsSource

XAML
<Window.Resources>
        <DataTemplate x:Key="DataTempItemsSource">
            <ComboBox HorizontalAlignment="Center" VerticalAlignment="Center" ItemsSource="{Binding ItemsList}" DisplayMemberPath="Name"
                  SelectedValuePath="Name" SelectedIndex="0"/>
        </DataTemplate>

<ListBox HorizontalAlignment="Center" 
                 VerticalAlignment="Center"
                 ItemTemplate="{StaticResource DataTempItemsSource}"
                 ItemsSource="{Binding ItemsList}">
        </ListBox>

This is the ComboBox with hardcoded values which are working as it should

XAML
<DataTemplate x:Key="DataTempHardCode">
            <ComboBox HorizontalAlignment="Center" VerticalAlignment="Center" SelectedIndex="0">
                <ComboBoxItem Content="One"/>
                <ComboBoxItem Content="Two"/>
            </ComboBox>
        </DataTemplate>

<ListBox HorizontalAlignment="Center" 
                 VerticalAlignment="Center"
                 ItemTemplate="{StaticResource DataTempHardCode}"
                 ItemsSource="{Binding ItemsList}">
        </ListBox>

I have also confirmed that the ComboBox with ItemsSource is working outside the DataTemplate.

<ComboBox HorizontalAlignment="Center" VerticalAlignment="Center" ItemsSource="{Binding ItemsList}" DisplayMemberPath="Name"
                  SelectedValuePath="Name" SelectedIndex="0"/>

I get theese two errors: System.Windows.Data Error: 40 : BindingExpression path error: 'ItemsList' property not found on 'object' ''ListEntry' (HashCode=20917673)'. BindingExpression:Path=ItemsList; DataItem='ListEntry' (HashCode=20917673); target element is 'ComboBox' (Name=''); target property is 'ItemsSource' (type 'IEnumerable')

System.Windows.Data Error: 40 : BindingExpression path error: 'ItemsList' property not found on 'object' ''ListEntry' (HashCode=52252659)'. BindingExpression:Path=ItemsList; DataItem='ListEntry' (HashCode=52252659); target element is 'ComboBox' (Name=''); target property is 'ItemsSource' (type 'IEnumerable')

Any ideas what is wrong? My other bindings are working so I don´t think the DataContext is wrong (it is set in the MainWindow.cs file: DataContext = this.dataClass;)

Why do you want to have a list of items where each item is displayed as a combobox of all the items? — Ackdari
Because I have a ListBox with ListBoxItems where you can select differrent options from a DropDown menu (the ComboBox) indivudually on each item. There are more elements in the ListBoxItems, they just aren´t included in my question. Good question by the way! — Ramriez

emybob emybob · Accepted Answer · 2019-08-02T13:50:07

When you create a control in a datatemplate, the datacontext of the control doesn't use the window's context, it use's the context of the control the template is used in. So when your listbox shows a list of ListEntitys, the combobox is trying to get an ItemsList property from each ListEntity - which doesn't exist

One way to fix this is to make your combobox use the window context:

ItemsSource="{Binding Path=DataContext.ItemsList, RelativeSource={RelativeSource AncestorType=Window}}"

How to bind ItemsSource to ComboBox within a DataTemplate

1 Answers