TemplateBinding DataContext in silverlight CustomControl

Question

I have a rather interesting case with ComboBox control - CustomComboBox;

In the style of this ComboBox, Popup contains one custom control that requests a DataContext;

<ctrl:CustomGrid DataContext="{TemplateBinding DataContext}" GridName="{Binding Preferences.CurrentGridName}"/>

The idea:

• to use this control several times on one page
• to use it in a masterpage container
• the masterpage control needs to have different DataContexts regarding the Page it is on

The logic:

• In the overriden OnApplyTemplate I am getting the grid and connecting few eventhandlers

The problem:

• The masterpage control is triggering OnApplyTemplate only once
• The first appearance of the CustomComboBox is as expected. However, every next apearance is with same DataContext, even when changing the datacontext of the CustomComboBox These changes don't reach to change my CustomGrid DataContext

I am sure that something on the bindings or the presentation logic is bad... Please throw some thoughts on, I would appreciate a hint here

Thanks

Answer 1

OnApplyTemplate is called when a ControlTemplate is applied to the control that overrides the method (neither its parent, nor children). If OnApplyTemplate is entered once, the overriding control must also be created once. I mean you simply have a single masterpage instance. This shouldn't be unexpected.

Speaking about Popups and DataContext, there often are issues with bindings from a Popup to outside it. So, I would rather write some code-behind to deliver correct context to Popups, instead of relying on Bindings. There sure is a problem of DataContextChanged event absence prior to SL5. To workaround this one, you should define your custom DependencyProperty on your CustomComboBox, bind it to the CustomComboBox's context and assign its value to the Popup in the PropertyChangedCallback.