add more context rich exceptions around failed navigation

src/Prism.Maui/Mvvm/ViewCreationException.cs

@@ -0,0 +1,22 @@
+using Prism.Common;
+
+namespace Prism.Mvvm;
+
+public class ViewCreationException : Exception
+{
+    public ViewCreationException(string viewName, ViewType viewType)
+        : this(viewName, viewType, null)
+    {
+    }
+
+    public ViewCreationException(string viewName, ViewType viewType, Exception innerException)
+        : base($"Unable to create {viewType} '{viewName}'.", innerException)
+    {
+        ViewName = viewName;
+        ViewType = viewType;
+    }
+
+    public ViewType ViewType { get; }
+
+    public string ViewName { get; }
+}

src/Prism.Maui/Mvvm/ViewModelCreationException.cs

@@ -0,0 +1,18 @@
+namespace Prism.Mvvm;
+
+public class ViewModelCreationException : Exception
+{
+    public ViewModelCreationException(object view, Exception innerException)
+        : base($"Unable to Create ViewModel for '{view.GetType().FullName}'.", innerException)
+    {
+        if (view is VisualElement visualElement)
+        {
+            View = visualElement;
+            ViewName = (string)visualElement.GetValue(ViewModelLocator.NavigationNameProperty);
+        }
+    }
+
+    public string ViewName { get; }
+
+    public VisualElement View { get; }
+}

src/Prism.Maui/Mvvm/ViewRegistryBase.cs

@@ -1,4 +1,5 @@
 using System.Text.RegularExpressions;
+using System.Xml.Linq;
 using Prism.Common;
 using Prism.Ioc;
 using Prism.Navigation.Xaml;
@@ -47,9 +48,13 @@ public object CreateView(IContainerProvider container, string name)
         {
             throw;
         }
+        catch (ViewModelCreationException)
+        {
+            throw;
+        }
         catch (Exception ex)
         {
-            throw new Exception($"Unable to create {_registryType} '{name}'.", ex);
+            throw new ViewCreationException(name, _registryType, ex);
         }
     }
 

src/Prism.Maui/Navigation/NavigationException.cs

@@ -9,10 +9,14 @@ public class NavigationException : Exception
     public const string IConfirmNavigationReturnedFalse = "IConfirmNavigation returned false";
     public const string NoPageIsRegistered = "No Page has been registered with the provided key";
     public const string ErrorCreatingPage = "An error occurred while resolving the page. This is most likely the result of invalid XAML or other type initialization exception";
+    public const string UnsupportedMauiCreation = "An unsupported Maui Exception occurred. This may be due to a bug with MAUI or something that is otherwise not supported by MAUI.";
+    public const string UnsupportedMauiNavigation = "An unsupported event occurred while Navigating. The attempted Navigation Stack is not supported by .NET MAUI";
+    public const string ErrorCreatingViewModel = "A dependency issue occurred while resolving the ViewModel. Check the InnerException for the ContainerResolutionException";
     public const string MvvmPatternBreak = "You have referenced a View type and are likely breaking the MVVM pattern. You should never reference a View type from a ViewModel.";
     public const string UnknownException = "An unknown error occurred. You may need to specify whether to Use Modal Navigation or not.";
 
     public NavigationException()
+        : this(UnknownException)
     {
     }
 
@@ -21,8 +25,8 @@ public NavigationException(string message)
     {
     }
 
-    public NavigationException(string message, Page page)
-        : this(message, page, null)
+    public NavigationException(string message, VisualElement view)
+        : this(message, view, null)
     {
     }
 
@@ -36,18 +40,18 @@ public NavigationException(string message, string navigationKey, Exception inner
     {
     }
 
-    public NavigationException(string message, Page page, Exception innerException) 
-        : this(message, null, page, innerException)
+    public NavigationException(string message, VisualElement view, Exception innerException) 
+        : this(message, null, view, innerException)
     {
     }
 
-    public NavigationException(string message, string navigationKey, Page page, Exception innerException) : base(message, innerException)
+    public NavigationException(string message, string navigationKey, VisualElement view, Exception innerException) : base(message, innerException)
     {
-        Page = page;
+        View = view;
         NavigationKey = navigationKey;
     }
 
-    public Page Page { get; }
+    public VisualElement View { get; }
 
     public string NavigationKey { get; }
 }

src/Prism.Maui/Navigation/PageNavigationService.cs

@@ -708,14 +708,32 @@ protected virtual Page CreatePage(string segmentName)
 
             return page;
         }
+        catch(NavigationException)
+        {
+            throw;
+        }
+        catch(KeyNotFoundException knfe)
+        {
+            throw new NavigationException(NavigationException.NoPageIsRegistered, segmentName, knfe);
+        }
+        catch(ViewModelCreationException vmce)
+        {
+            throw new NavigationException(NavigationException.ErrorCreatingViewModel, segmentName, _pageAccessor.Page, vmce);
+        }
+        //catch(ViewCreationException viewCreationException)
+        //{
+        //    if(!string.IsNullOrEmpty(viewCreationException.InnerException?.Message) && viewCreationException.InnerException.Message.Contains("Maui"))
+        //        throw new NavigationException(NavigationException.)
+        //}
         catch (Exception ex)
         {
-            if (ex is NavigationException)
-                throw;
-
-            else if(ex is KeyNotFoundException)
-                throw new NavigationException(NavigationException.NoPageIsRegistered, segmentName, ex);
-
+            var inner = ex.InnerException;
+            while(inner is not null)
+            {
+                if (inner.Message.Contains("thread with a dispatcher"))
+                    throw new NavigationException(NavigationException.UnsupportedMauiCreation, segmentName, _pageAccessor.Page, ex);
+                inner = inner.InnerException;
+            }
             throw new NavigationException(NavigationException.ErrorCreatingPage, segmentName, ex);
         }
     }
@@ -727,7 +745,7 @@ protected virtual Page CreatePageFromSegment(string segment)
         if (page is null)
         {
             var innerException = new NullReferenceException(string.Format("{0} could not be created. Please make sure you have registered {0} for navigation.", segmentName));
-            throw new NavigationException(NavigationException.NoPageIsRegistered, _pageAccessor.Page, innerException);
+            throw new NavigationException(NavigationException.NoPageIsRegistered, segmentName, _pageAccessor.Page, innerException);
         }
 
         return page;
@@ -937,71 +955,75 @@ await DoNavigateAction(onNavigatedFromTarget, segment, nextPage, parameters, asy
             await ProcessNavigation(currentPage.Navigation.NavigationStack.Last(), illegalSegments, parameters, true, animated);
     }
 
-    protected virtual Task DoPush(Page currentPage, Page page, bool? useModalNavigation, bool animated, bool insertBeforeLast = false, int navigationOffset = 0)
+    protected virtual async Task DoPush(Page currentPage, Page page, bool? useModalNavigation, bool animated, bool insertBeforeLast = false, int navigationOffset = 0)
     {
         if (page is null)
             throw new ArgumentNullException(nameof(page));
 
-        // Prevent Page from using Parent's ViewModel
-        if (page.BindingContext is null)
-            page.BindingContext = new object();
-
-        if (currentPage is null)
+        try
         {
-            if (_application.Windows.OfType<PrismWindow>().Any(x => x.Name == PrismWindow.DefaultWindowName))
-                _window = _application.Windows.OfType<PrismWindow>().First(x => x.Name == PrismWindow.DefaultWindowName);
+            // Prevent Page from using Parent's ViewModel
+            if (page.BindingContext is null)
+                page.BindingContext = new object();
 
-            if (Window is null)
+            if (currentPage is null)
             {
-                _window = new PrismWindow
+                if (_application.Windows.OfType<PrismWindow>().Any(x => x.Name == PrismWindow.DefaultWindowName))
+                    _window = _application.Windows.OfType<PrismWindow>().First(x => x.Name == PrismWindow.DefaultWindowName);
+
+                if (Window is null)
+                {
+                    _window = new PrismWindow
+                    {
+                        Page = page
+                    };
+                    ((List<Window>)_application.Windows).Add(_window as PrismWindow);
+                }
+                else
                 {
-                    Page = page
-                };
-                ((List<Window>)_application.Windows).Add(_window as PrismWindow);
-            }
-            else
-            {
 #if !ANDROID
-                // BUG: https://github.com/dotnet/maui/issues/7275
-                Window.Page = page;
+                    // BUG: https://github.com/dotnet/maui/issues/7275
+                    Window.Page = page;
 #if WINDOWS
-                page.ForceLayout();
+                    page.ForceLayout();
 #endif
 #else
-
-                // HACK: This is the only way CURRENTLY to ensure that the UI resets for Absolute Navigation
-                var newWindow = new PrismWindow
-                {
-                    Page = page
-                };
-                _application.OpenWindow(newWindow);
-                _application.CloseWindow(Window);
-                _window = null;
+                    // HACK: This is the only way CURRENTLY to ensure that the UI resets for Absolute Navigation
+                    var newWindow = new PrismWindow
+                    {
+                        Page = page
+                    };
+                    _application.OpenWindow(newWindow);
+                    _application.CloseWindow(Window);
+                    _window = null;
 #endif
-            }
-
-            return Task.FromResult<object>(null);
-        }
-        else
-        {
-            bool useModalForPush = UseModalNavigation(currentPage, useModalNavigation);
-
-            if (useModalForPush)
-            {
-                return currentPage.Navigation.PushModalAsync(page, animated);
+                }
             }
             else
             {
-                if (insertBeforeLast)
+                bool useModalForPush = UseModalNavigation(currentPage, useModalNavigation);
+
+                if (useModalForPush)
                 {
-                    return InsertPageBefore(currentPage, page, navigationOffset);
+                    await currentPage.Navigation.PushModalAsync(page, animated);
                 }
                 else
                 {
-                    return currentPage.Navigation.PushAsync(page, animated);
+                    if (insertBeforeLast)
+                    {
+                        await InsertPageBefore(currentPage, page, navigationOffset);
+                    }
+                    else
+                    {
+                        await currentPage.Navigation.PushAsync(page, animated);
+                    }
                 }
             }
         }
+        catch (Exception ex)
+        {
+            throw new NavigationException(NavigationException.UnsupportedMauiNavigation, _pageAccessor.Page, ex);
+        }
     }
 
     protected virtual Task InsertPageBefore(Page currentPage, Page page, int pageOffset)

src/Prism.Maui/PrismAppBuilder.cs

@@ -72,12 +72,19 @@ private void ConfigureViewModelLocator(IContainerProvider container)
 
     internal static object DefaultViewModelLocator(object view, Type viewModelType)
     {
-        if (view is not BindableObject bindable)
-            return null;
+        try
+        {
+            if (view is not BindableObject bindable)
+                return null;
 
-        var container = bindable.GetContainerProvider();
+            var container = bindable.GetContainerProvider();
 
-        return container.Resolve(viewModelType);
+            return container.Resolve(viewModelType);
+        }
+        catch (Exception ex)
+        {
+            throw new ViewModelCreationException(view, ex);
+        }
     }
 
     public PrismAppBuilder RegisterTypes(Action<IContainerRegistry> registerTypes)