WPF Repeater (like) control for collection source?

Question

I have a WPF DataGrid bound to ObservableCollection. Each item in my collection has Property which is a List. In m

Answer 1

What you did by specifying <DataTemplate .../> inside of ItemsControl is you added this instance of DataTemplate to default property of ItemsControl which is Items. So the exception you got is the expected result: first you specify the ItemsSource, then you modify Items. Instead you should modify ItemTemplate property on your ItemsControl like so:

<ItemsControl ItemsSource="{Binding Path=Exchanges}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Label>test</Label>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal"/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
</ItemsControl>