Microsoft-ui-xaml: Proposal: Update NavigationView to use ItemsRepeater

[YuliKl]

Proposal: Update NavigationView to use ItemsRepeater

Summary

Instead of ListView, perhaps NavigationView should use ItemsRepeater as an implementation detail. This shouldn't have any direct impact on users but would help clean up the code.

Rationale

Currently NavigationView has a dependency on ListView in order to display the MenuItems. This becomes a drawback in places where we have to circumvent some of ListView's existing behaviors which results in complicated codepaths and is a way for bugs to be introduced.

Pros to moving to ItemsRepeater:

• Greater control over selection behavior which will result in cleaner code. Currently item selection logic is tangled up with the ListView selection logic
  
  
  
  • Have to keep track of selection state in two different locations. We have to manage and sync selection when it is changed using NavigationView API or when it is changed in the ListView.
  
  
  • Have to deal with callbacks for scenarios where we don’t want selection on invocation
  
  
  • Moving items in and out of a listview also sometimes influences selection
  
  
• Item-repeater is less policy-heavy. Less restrictions can potentially mean less problems when implementing other future functionality. This is an advantage for Top and Hierarchical Navigation as these features are not based on a single listview and require movement of items. This flexibility also gives us a greater control over functionality such as animations.
• Circumvents ListView pre-rs5 bug which manifests in databinding scenarios when adding a container as the root of the datatemplate.

Cons to moving to ItemsRepeater:

• Have to re-implement behavior that is handled by listview
  
  
  
  • Selection
  
  
  • Item Invocation
  
  
  • Container - Item mapping
  
  
  • Markup VS Databinding scenarios
    
    
    
    
    
    • since ItemsRepeater only takes an ItemsSource, we would have to handle the scenarios where either the menuitems are declared in MarkUp or the ItemsSource requires default container wrapping (NavigationViewItem)
    
    
    
  
  
  • AutomationPeer
  
  
  • ItemContainerStyle/ItemContainerStyleSelector
  
  
• Scenarios where previous app implementations are dependent on ListView functionality (such as SelectorItem.IsSelected) would get broken. Would have to write supporting code for these issues.

Functional Requirements

Important Notes

Open Questions

[jevansaks]

@ojhad Can you add some details about the pro/cons of this? We talked about it offline and it seems righteous but is it worth the cost?

[chingucoding]

I think this proposal was addressed with #1683 and can be closed.