
Hi Christoph,
We actually tried to mimic the native WinForms DateTimePicker in that respect, which also has the CheckBox as a focusable/tab stop control. In addition, it will only toggle the CheckBox when the CheckBox has focus, like ours.
In our DateTimeEditBox, if the CheckBox is not checked (or not even visible) you can still tab over to start entering data. If you set IsNullAllowed to true, then you can "null out" the value using Ctrl+A (select all) and pressing the Delete key.
You can define the following DataTemplate and assign it to the CheckBoxTemplate property to make the CheckBox not a tab stop:
xmlns:editors="http://schemas.actiprosoftware.com/winfx/xaml/editors"
xmlns:themes="http://schemas.actiprosoftware.com/winfx/xaml/themes"
<DataTemplate x:Key="CustomCheckBoxTemplate">
<CheckBox VerticalAlignment="Center" Padding="0" IsTabStop="False"
Style="{DynamicResource {x:Static themes:EditorsCommonDictionary.CheckBoxStyleKey}}"
IsChecked="{Binding IsChecked, RelativeSource={x:Static editors:PartEditBox.RelativeSource}}" />
</DataTemplate>