ListBox ItemTempate DataContext

Question

Hello, I have a ListBox which has its ViewModel - let's call it ListBoxViewModel. List box has ItemsSource="{Binding MyItems}" attribute which corresponds to ObservableCollection<MyItemType> in ListBoxViewModel. ListBox has its ItemTemplate which creates MyItemControl controls in ListBox. The question is that I expect that MyItemControl has MyItemType instance as DataContext. But DataContext is null. What is the best implementation?

Answer 1

Set the data context explictly

Answer 2

I had just wrong syntax somewhere. Correct solution example is:

App.xaml

<Application x:Class="WpfProblem2.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfProblem2"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <DataTemplate x:Key="myTemplate">
            <local:MyItemControl/>
        </DataTemplate>
    </Application.Resources>
</Application>

ListBoxViewModel.cs

namespace WpfProblem2 {
    public class ListBoxViewModel : DependencyObject {

        public ListBoxViewModel() {
            MyItems = new ObservableCollection<MyItemType>() {
                new MyItemType() { TextValue = "A" },
                new MyItemType() { TextValue = "B" },
                new MyItemType() { TextValue = "C" },
                new MyItemType() { TextValue = "D" }
            };
        }

        public ObservableCollection<MyItemType> MyItems { get; private set; }
    }
}

MainWindow.xaml

<Window x:Class="WpfProblem2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded">
    <ListBox x:Name="listBox" ItemTemplate="{StaticResource myTemplate}" ItemsSource="{Binding MyItems}" />
</Window>

MainWindow.xaml.cs

namespace WpfProblem2 {
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e) {
            listBox.DataContext = new ListBoxViewModel();
        }
    }
}

MyItemControl.xaml

<UserControl x:Class="WpfProblem2.MyItemControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="50" d:DesignWidth="300">
    <TextBox Text="{Binding TextValue}" />
</UserControl>

MyItemType.cs

namespace WpfProblem2 {
    public class MyItemType : DependencyObject {

        public static readonly DependencyProperty TextValueProperty = DependencyProperty.Register("TextValue", typeof(string), typeof(MyItemType));
        public string TextValue {
            get { return (string)GetValue(TextValueProperty); }
            set { SetValue(TextValueProperty, value); }
        }

    }
}