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Fix for MAUI RoutedViewHost (#3303)
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* Fix for MAUI RoutedViewHost

* Update RoutedViewHost.cs

* Setting Page.Title prevents binding

* Fix code style warnings

* Fix cross thread issue with Title

* Add missing using

* Add SetTitleOnNavigate property

Use ObserveOn(RxApp.MainThreadScheduler) and RxApp.MainThreadScheduler.Schedule to handle cross threading.

* Add missing usings

* Added missing using

Co-authored-by: Glenn <[email protected]>
Co-authored-by: Chris Pulman <[email protected]>
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@ili @glennawatson @ChrisPulman
3 people authored Jul 8, 2022
1 parent 196b8a6 commit 8fa79d1
Showing 1 changed file with 159 additions and 107 deletions.
266 changes: 159 additions & 107 deletions src/ReactiveUI.Maui/RoutedViewHost.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,9 +6,9 @@
using System;
using System.Diagnostics.CodeAnalysis;
using System.Reactive;
using System.Reactive.Concurrency;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Reactive.Threading.Tasks;
using System.Reflection;
using Microsoft.Maui.Controls;
using Splat;
Expand All @@ -32,6 +32,15 @@ public class RoutedViewHost : NavigationPage, IActivatableView, IEnableLogger
typeof(RoutedViewHost),
default(RoutingState));

/// <summary>
/// The Set Title on Navigate property.
/// </summary>
public static readonly BindableProperty SetTitleOnNavigateProperty = BindableProperty.Create(
nameof(SetTitleOnNavigate),
typeof(bool),
typeof(RoutedViewHost),
false);

/// <summary>
/// Initializes a new instance of the <see cref="RoutedViewHost"/> class.
/// </summary>
Expand All @@ -40,80 +49,31 @@ public RoutedViewHost()
{
this.WhenActivated(disposable =>
{
var currentlyPopping = false;
var popToRootPending = false;
var userInstigated = false;

this.WhenAnyObservable(x => x.Router.NavigationChanged)
.Where(_ => Router.NavigationStack.Count == 0)
.Select(x =>
{
// Xamarin Forms does not let us completely clear down the navigation stack
// instead, we have to delay this request momentarily until we receive the new root view
// then, we can insert the new root view first, and then pop to it
popToRootPending = true;
return x;
})
.Subscribe()
.DisposeWith(disposable);
var currentlyNavigating = false;

Router?
.NavigationChanged?
.CountChanged()
.Select(_ => Router.NavigationStack.Count)
.StartWith(Router.NavigationStack.Count)
.Buffer(2, 1)
.Select(counts => new
.NavigateBack
.Subscribe(async _ =>
{
Delta = counts[0] - counts[1],
Current = counts[1],
try
{
currentlyNavigating = true;
await PopAsync();
}
finally
{
currentlyNavigating = false;
}

// cache current viewmodel as it might change if some other Navigation command is executed midway
CurrentViewModel = Router.GetCurrentViewModel()
InvalidateCurrentViewModel();
SyncNavigationStacks();
})
.Where(_ => !userInstigated)
.Where(x => x.Delta > 0)
.Select(
async x =>
{
// XF doesn't provide a means of navigating back more than one screen at a time apart from navigating right back to the root page
// since we want as sensible an animation as possible, we pop to root if that makes sense. Otherwise, we pop each individual
// screen until the delta is made up, animating only the last one
var popToRoot = x.Current == 1;
currentlyPopping = true;

try
{
if (popToRoot)
{
await PopToRootAsync(true);
}
else if (!popToRootPending)
{
for (var i = 0; i < x.Delta; ++i)
{
await PopAsync(i == x.Delta - 1);
}
}
}
finally
{
currentlyPopping = false;
if (CurrentPage is IViewFor page && x.CurrentViewModel is not null)
{
page.ViewModel = x.CurrentViewModel;
}
}

return Unit.Default;
})
.Concat()
.Subscribe()
.DisposeWith(disposable);

Router?
.Navigate
.SelectMany(_ => PageForViewModel(Router.GetCurrentViewModel()))
.ObserveOn(RxApp.MainThreadScheduler)
.SelectMany(_ => PagesForViewModel(Router.GetCurrentViewModel()))
.SelectMany(async page =>
{
var animated = true;
Expand All @@ -123,17 +83,18 @@ public RoutedViewHost()
animated = false;
}

if (popToRootPending && Navigation.NavigationStack.Count > 0)
try
{
Navigation.InsertPageBefore(page, Navigation.NavigationStack[0]);
await PopToRootAsync(animated);
currentlyNavigating = true;
await PushAsync(page, animated);
}
else
finally
{
await PushAsync(page, animated);
currentlyNavigating = false;
}

popToRootPending = false;
SyncNavigationStacks();

return page;
})
.Subscribe()
Expand All @@ -151,26 +112,37 @@ public RoutedViewHost()
// NB: Catch when the user hit back as opposed to the application
// requesting Back via NavigateBack
poppingEvent
.Where(_ => !currentlyPopping && Router is not null)
.Where(_ => !currentlyNavigating && Router is not null)
.Subscribe(_ =>
{
userInstigated = true;

try
{
Router?.NavigationStack.RemoveAt(Router.NavigationStack.Count - 1);
}
finally
{
userInstigated = false;
}
Router!.NavigationStack.RemoveAt(Router.NavigationStack.Count - 1);

InvalidateCurrentViewModel();
})
.DisposeWith(disposable);

var poppingToRootEvent = Observable.FromEvent<EventHandler<NavigationEventArgs>, Unit>(
eventHandler =>
{
void Handler(object? sender, NavigationEventArgs e) => eventHandler(Unit.Default);
return Handler;
},
x => PoppedToRoot += x,
x => PoppedToRoot -= x);

var vm = Router?.GetCurrentViewModel();
if (CurrentPage is IViewFor page && vm is not null)
// NB: Catch when the user hit back as opposed to the application
// requesting Back via NavigateBack
poppingToRootEvent
.Where(_ => !currentlyNavigating && Router is not null)
.Subscribe(_ =>
{
for (var i = Router!.NavigationStack.Count - 1; i > 0; i--)
{
// don't replace view model if vm is null
page.ViewModel = vm;
Router.NavigationStack.RemoveAt(i);
}

InvalidateCurrentViewModel();
})
.DisposeWith(disposable);
});
Expand All @@ -182,24 +154,6 @@ public RoutedViewHost()
}

Router = screen.Router;

this.WhenAnyValue(x => x.Router)
.SelectMany(router => router!.NavigationStack
.ToObservable()
.Select(x => (Page)ViewLocator.Current.ResolveView(x)!)
.SelectMany(x => PushAsync(x).ToObservable())
.Finally(() =>
{
var vm = router.GetCurrentViewModel();
if (vm is null)
{
return;
}

((IViewFor)CurrentPage).ViewModel = vm;
CurrentPage.Title = vm.UrlPathSegment;
}))
.Subscribe();
}

/// <summary>
Expand All @@ -211,13 +165,22 @@ public RoutingState Router
set => SetValue(RouterProperty, value);
}

/// <summary>
/// Gets or sets a value indicating whether gets or sets the Set Title of the view model stack.
/// </summary>
public bool SetTitleOnNavigate
{
get => (bool)GetValue(SetTitleOnNavigateProperty);
set => SetValue(SetTitleOnNavigateProperty, value);
}

/// <summary>
/// Pages for view model.
/// </summary>
/// <param name="vm">The vm.</param>
/// <returns>An observable of the page associated to a <see cref="IRoutableViewModel"/>.</returns>
[SuppressMessage("Design", "CA1822: Can be made static", Justification = "Might be used by implementors.")]
protected IObservable<Page> PageForViewModel(IRoutableViewModel? vm)
protected virtual IObservable<Page> PagesForViewModel(IRoutableViewModel? vm)
{
if (vm is null)
{
Expand All @@ -235,8 +198,97 @@ protected IObservable<Page> PageForViewModel(IRoutableViewModel? vm)
ret.ViewModel = vm;

var pg = (Page)ret;
pg.Title = vm.UrlPathSegment;
if (SetTitleOnNavigate)
{
pg.Title = vm.UrlPathSegment;
}

return Observable.Return(pg);
}
}

/// <summary>
/// Page for view model.
/// </summary>
/// <param name="vm">The vm.</param>
/// <returns>An observable of the page associated to a <see cref="IRoutableViewModel"/>.</returns>
[SuppressMessage("Design", "CA1822: Can be made static", Justification = "Might be used by implementors.")]
protected virtual Page PageForViewModel(IRoutableViewModel vm)
{
if (vm is null)
{
throw new ArgumentNullException(nameof(vm));
}

var ret = ViewLocator.Current.ResolveView(vm);
if (ret is null)
{
var msg = $"Couldn't find a View for ViewModel. You probably need to register an IViewFor<{vm.GetType().Name}>";

throw new Exception(msg);
}

ret.ViewModel = vm;

var pg = (Page)ret;

if (SetTitleOnNavigate)
{
RxApp.MainThreadScheduler.Schedule(() => pg.Title = vm.UrlPathSegment);
}

return pg;
}

/// <summary>
/// Invalidates current page view model.
/// </summary>
protected void InvalidateCurrentViewModel()
{
var vm = Router?.GetCurrentViewModel();
if (CurrentPage is IViewFor page && vm is not null)
{
// don't replace view model if vm is null
page.ViewModel = vm;
}
}

/// <summary>
/// Syncs page's navigation stack with <see cref="Router"/>
/// to affect <see cref="Router"/> manipulations like Add or Clear.
/// </summary>
protected void SyncNavigationStacks()
{
if (Navigation.NavigationStack.Count != Router.NavigationStack.Count
|| StacksAreDifferent())
{
for (var i = Navigation.NavigationStack.Count - 2; i >= 0; i--)
{
Navigation.RemovePage(Navigation.NavigationStack[i]);
}

var rootPage = Navigation.NavigationStack[0];

for (var i = 0; i < Router.NavigationStack.Count - 1; i++)
{
var page = PageForViewModel(Router.NavigationStack[i]);
Navigation.InsertPageBefore(page, rootPage);
}
}
}

private bool StacksAreDifferent()
{
for (var i = 0; i < Router.NavigationStack.Count; i++)
{
var vm = Router.NavigationStack[i];
var page = Navigation.NavigationStack[i];

if (page is not IViewFor view || !ReferenceEquals(view.ViewModel, vm))
{
return true;
}
}

return false;
}
}

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