CommandBar Extensions

[kazo0]

The CommandBar Extensions need to be cleaned up and some can be merged under better defined contracts like an AppBarButton. Below is a proposal of the new Attached Properties and some notes on how they would be implemented.

The naming of the BackButtonTitle will be changed to CurrentPageTitle to better reflect its actual behaviour. This property relates to the title of the back button on the next page in the stack on iOS. So, setting CurrentPageTitle to "Test123" on Page A's CommandBar then forward-navigating to Page B from Page A will now set the back button's title to "Test123", indicating that you would be navigation back to a page titled "Test123" (Page A).

Option 1

We will consolidate most of the properties into the NavigationCommand Property and rename it to NavigationButton. The CommandBarRenderers (iOS/Android) will read the Icon and Foreground properties of the AppBarButton and map to the native properties of the native back button.

Attached Property	Type	Android	iOS
NavigationButton	AppBarButton	X	X
IsNavigationButtonAttached	bool	X	X
CurrentPageTitle	string		X
Subtitle	string	X

• The NavigationButton's Icon and Foreground properties will be used to set the icon and colour of the native back button. The native back button will be completely replaced with this AppBarButton if IsNavigationButtonAttached is true.
• IsNavigationButtonAttached: Determines whether or not the AppBarButton is actually attached to the native CommandBar. This will replace the native back button and disabled the native back gesture.
• CurrentPageTitle (iOS Only): Value to be used by the back button of the next page
• Subtitle (Android Only): The subtitle is displayed below the native title. The colour of the subtitle can't be changed.

Option 2

We will keep the NavigationCommand behaviour the same, except for its name which will change to NavigationButton. Along with the NavigationButton, we will add a new AppBarButton called BackButton that will consolidation the current BackButtonIcon and BackButtonForeground

Attached Property	Type	Android	iOS
NavigationButton	AppBarButton	X	X
BackButton	AppBarButton	X	X
CurrentPageTitle	string		X
Subtitle	string	X

• The BackButton's Icon and Foreground properties will be used to set the icon and colour of the native back button
• CurrentPageTitle (iOS Only): Value to be used by the back button of the next page
• Subtitle (Android Only): The subtitle is displayed below the native title. The colour of the subtitle can't be changed.

[kazo0]

Attached Property	Type	Android	iOS
NavigationButton	AppBarButton	X	X
NavigationButtonMode	NavigationButtonMode	X	X

NavigationButtonMode will be an enum with two values: Native and Override. Native will be the default mode, where we will not actually replace the native back button with the provided NavigationButton. Override will actually replace the native back button with the NavigationButton, in order to achieve things like custom logic on button pressed, burger menu, etc.

[robloo]

How does this relate with #6195 ?

Honestly, the WinUI CommandBar code is what is needed most. When this comes in, the existing (highly restrictive) CommandBar should likely be removed. The CommandBar implementation currently in Uno is likely best left to platform-specific code in my opinion. It functions like a MAUI wrapped control and isn't suited to the design objectives of Uno (pixel-perfect, WinUI compatible).

I expect Uno uses this implementation a lot internally so it could be pulled out into a separate control and left in. I just think it shouldn't be the default CommandBar implementation. It seems to create many more problems than it solves for those of us with existing code.