Why IntelliSense doesn't show the item's properties with DataGrid built-in columns?

Question

I have this ViewModel classes:

public class Item
{
    public string ItemName { get; set; }
}

public class Container
{
    public string ContainerName { get; set; }
    public List<Item> Items { get; }
}

I use them in the XAML of my Window to help the IntelliSense at DesignTime:

<Window x:Class="DesignTime.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:DesignTime"
        mc:Ignorable="d"
        d:DataContext="{d:DesignInstance Type=local:Container, IsDesignTimeCreatable=True}"/>

Now the IntelliSense recognizes the properties of the Container:

So I create an ItemsControl bound to the Items list of the Container. When I write the bindings of the DataTemplate of the single displayed item, the IntelliSense now shows me the properties of the Item class:

The same happens if I use a ListBox or a ListView.

But with a DataGrid something goes wrong. If I create a column with a built-in template, like DataGridTextColumn, the IntelliSense shows me the Container's properties, not the Item's one!

Same for the other built-in columns: DataGridCheckBoxColumn, etc.

However, if I write a custom template using the DataGridTemplateColumn, it works well like the ItemsControl.

Why is this happening? How can I make the IntelliSense to work correctly with the DataGrid's built-in columns (if it's possible)?

Answer 1

Why is this happening?

Probably because a DataGridColumn is not a FrameworkElement that gets added to the visual tree. It doesn't have a DataContext. The root element of a DataTemplate does get added to the visual tree and has a DataContext though. That's the difference.

Your answer seems reasonable, but there's a thing that I still found weird. I would expect an implicit DataTemplate also for built-in columns like DataGridCheckBoxColumn. How could it be rendered as a CheckBox otherwise?

The CheckBox is built eventually at runtime, not at design time. The designer doesn't run all code that is executed at runtime.