.net maui custom control handlers, how to convert Content between virtualview and platformview-CodePudding

I am trying to create a custom Maui Handler for WinUI3 NavigationView.

I have defined the mapping from the virtualView to the PlatformView but i cant seem to convert the Virtual view Content to the PlatformView Content,

An example would be I have a NavigationView.Content = Microsoft.Maui.Frame.Content.

Looking through the maui code there seems to be some mappers but i cant figure out how to get these invoked.

Here is my current code

public static void MapContent(IZtNavigationViewHandler viewHandler, IZtNavigationView virtualView) 
{ 
  ((NavigationView)(viewHandler?.PlatformView)).Content = virtualView.Content; 
}

The mapper is being called but it cant convert the content correctly

Any Ideas or pointers?

CodePudding user response：

TL;DR The lines in a hand-written custom handler’s mapper method, where Content is mapped:

    if (handler.VirtualView.PresentedContent is IView view) 
        handler.PlatformView.Children.Add(view.ToPlatform(handler.MauiContext));

OR if PlatformView has a Content property (NavigationView does), then:

    if (handler.VirtualView.PresentedContent is IView view) 
        handler.PlatformView.Content = view.ToPlatform(handler.MauiContext);

Approach 3 would use that syntax.

First, Frame, ListView, and TableView are "legacy" Renderer-based views. They don't use handlers.

Don't use one of those.

Try ContentView as the virtual view.
In Maui source, ContentViewHandler.Windows.cs is the default behavior.

Given:

public class MyContentView : ContentView
{
}

Goal is to make a handler that maps MyContentView to WinUI3's NavigationView, and MyContentView.Content to NavigationView.Content.

ALTERNATIVE 1 - MyContentViewHandler

Similar to Customize specific control instances,
and similar to Maui source solution 'Microsoft.Maui' /
Controls / samples / Maui.Controls.Sample / Controls / BordelessEntry /
BordelessEntryHandler.cs.

One significant difference: Instead of mapping directly to a NavigationView, let MyContentView create ContentPanel (logic inherited from ContentViewHandler), then make NavigationView the child of ContentPanel.

using Microsoft.Maui;
using Microsoft.Maui.Handlers;
...
public class MyContentViewHandler : ContentViewHandler
{
    public static IPropertyMapper<IContentView, IContentViewHandler> Mapper =
        new PropertyMapper<IContentView, IContentViewHandler>(ViewMapper)
        {
            [nameof(IContentView.Content)] = MapContent,
        };
            
    public static void MapContent(IContentViewHandler handler, IContentView page)
    {
        UpdateContent(handler);
    }

    static void UpdateContent(IContentViewHandler handler)
    {
        _ = handler.PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
        _ = handler.VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
        _ = handler.MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} should have been set by base class.");

        handler.PlatformView.Children.Clear();

        if (handler.VirtualView.PresentedContent is IView view)
        {
            // platform equivalent to Content.
            var platformContent = view.ToPlatform(handler.MauiContext);
    #if WINDOWS
            // Wrap content in a NavigationView.
            var navView = new NavigationView();
            navView.Content = platformContent;
            handler.PlatformView.Children.Add(navView);
    #else
            handler.PlatformView.Children.Add(platformContent);
    #endif
        }
    }
}

ALTERNATIVE 2 - Mapper.AppendToMapping

INCOMPLETE ... not sure how/where to do this ...

Technique: AFTER standard mapping is performed, "fix up" MyContentView.

using Microsoft.UI.Xaml.Controls;

Microsoft.Maui.Handlers.ContentViewHandler.Mapper.AppendToMapping(
    "MyContentViewAsNavView", (handler, view) =>
    {
        if (view is MyContentView)
        {
    #if WINDOWS
            if (handler.PlatformView.Children.Count > 0) {
                // ASSUME first child is the Content to wrap.
                var platformContent = handler.PlatformView.Children[0];
                // Wrap content in a NavigationView.
                var navView = new NavigationView();
                navView.Content = platformContent;
                handler.PlatformView.Children[0] = navView;
            }
    #endif
        }
    });

ALTERNATIVE 3 - "NavigationPanel" adapter

(Instead of "nesting" NavigationView inside of ContentPanel.)

Copy Maui sources ContentViewHandler.cs and ContentViewHandler.Windows.cs, to MyContent... files.
Replace "ContentView" with "MyContentView" and "ContentPanel" with "NavigationView".
Observe that it won't compile. "CrossPlatformMeasure" and "CrossPlatformArrange" don't exist in "NavigationView".
Make a new class "NavigationPanel" to adapt "NavigationView". Equivalent of "ContentPanel" which adapts "Panel" for ContentView. Adapt from Microsoft.Maui.Platform.ContentPanel source.
Where you previously replaced "ContentPanel" with "NavigationView", instead use this new "NavigationPanel".

CodePudding user response：

Thanks to ToolmakerSteve I found out a direction to do it in.

The ControlView must inherit from both View and IContentView,

// So the interface would be 
 [ContentProperty("Content")]
public interface IMyControlView : IContentView
{}

// Then the Control must be constructed with 
public partial class MyControlView : View, IContentView, IMyControlView
{

// Then in the view implement the MapContent

public object Content 
        {
            get { return (View)GetValue(ContentProperty); }
            set { SetValue(ContentProperty, value); }
        }
// you must also implement PresentedContent
IView? IContentView.PresentedContent => (View)Content;
}

Then in your handler do the mapping for Content and expose it as

public partial class MyControlViewHandler : ViewHandler<MyControlView, ActualControl>, IMyControlViewHandler    
{
        public static void MapContent(IZtNavigationViewHandler handler, IZtNavigationView virtualView)
            {
                //((NavigationView)(viewHandler?.PlatformView)).Content = virtualView.Content;
                _ = handler.PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
                _ = handler.VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
                _ = handler.MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} should have been set by base class.");
    
    #if WINDOWS
                if (handler.VirtualView.PresentedContent is IView view)
                    handler.PlatformView.Content = view.ToPlatform(handler.MauiContext);
    #endif
            }
}

With this i was able to use the WinUI3 NavigationView with Content from ScrollView, BorderView, ContentView.

More to test but thanks for all the help