Align nullable parameter and dialog contracts

Directory.Build.props

@@ -23,6 +23,7 @@
       System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute;
       System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes;
       System.Diagnostics.CodeAnalysis.FeatureSwitchDefinitionAttribute;
+      System.Diagnostics.CodeAnalysis.MaybeNullAttribute;
       System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute;
       System.Runtime.CompilerServices.IsExternalInit;
     </PolySharpIncludeGeneratedTypes>

src/Maui/Prism.Maui/Behaviors/ElementParentedCallbackBehavior.cs

@@ -2,6 +2,7 @@
 using Prism.Extensions;
 using Prism.Navigation.Xaml;
 
+#nullable enable
 namespace Prism.Behaviors;
 
 internal class ElementParentedCallbackBehavior : Behavior<VisualElement>
@@ -30,7 +31,7 @@ internal class ElementParentedCallbackBehavior : Behavior<VisualElement>
         base.OnDetachingFrom(view);
     }
 
-    private void OnParentChanged(object sender, EventArgs e) => TryInvokeCallback();
+    private void OnParentChanged(object? sender, EventArgs e) => TryInvokeCallback();
 
     private void TryInvokeCallback()
     {
@@ -59,7 +60,7 @@ internal class ElementParentedCallbackBehavior : Behavior<VisualElement>
         while (scopePage?.Parent is FlyoutPage flyout && flyout.Flyout == scopePage)
             scopePage = flyout;
 
-        for (Element element = view; element is not null; element = element.Parent)
+        for (Element? element = view; element is not null; element = element.Parent)
         {
             _observedElements.Add(element);
             element.ParentChanged += OnParentChanged;
@@ -72,10 +73,10 @@ internal class ElementParentedCallbackBehavior : Behavior<VisualElement>
         }
     }
 
-    private Page GetPage(VisualElement view) =>
+    private Page? GetPage(VisualElement view) =>
         _includeSelf && view is Page page ? page : view.GetParentPage();
 
-    private void PagePropertyChanged(object sender, PropertyChangedEventArgs e)
+    private void PagePropertyChanged(object? sender, PropertyChangedEventArgs e)
     {
         if (e.PropertyName == Navigation.Xaml.Navigation.PrismContainerProvider)
             TryInvokeCallback();

src/Maui/Prism.Maui/Dialogs/DialogContainerPage.cs

@@ -8,6 +8,7 @@ using Prism.Dialogs.Xaml;
 using Application = Microsoft.Maui.Controls.Application;
 using Page = Microsoft.Maui.Controls.Page;
 
+#nullable enable
 namespace Prism.Dialogs;
 
 /// <summary>
@@ -57,12 +58,14 @@ public class DialogContainerPage : ContentPage, IDialogContainer
     /// <summary>
     /// Gets the dialog view displayed in the container page.
     /// </summary>
-    public View DialogView { get; private set; }
+    /// <remarks>Returns null until <see cref="ConfigureLayout"/> configures the dialog.</remarks>
+    public View? DialogView { get; private set; }
 
     /// <summary>
     /// Gets the command used to dismiss the dialog.
     /// </summary>
-    public ICommand Dismiss { get; private set; }
+    /// <remarks>Returns null until <see cref="ConfigureLayout"/> configures the dialog.</remarks>
+    public ICommand? Dismiss { get; private set; }
 
     /// <summary>
     /// Configures the layout of the dialog container page.
@@ -244,8 +247,11 @@ public class DialogContainerPage : ContentPage, IDialogContainer
     /// </summary>
     /// <param name="element">The element.</param>
     /// <returns>The style for the specified element.</returns>
-    private static Style GetStyle(Element element)
+    private static Style GetStyle(Element? element)
     {
+        if (element is null)
+            return DefaultStyle();
+
         if (element is Page page && page.Resources.ContainsKey(DialogLayout.PopupOverlayStyle) && page.Resources[DialogLayout.PopupOverlayStyle] is Style pageStyle)
             return pageStyle;
         else if (element is Application app)

src/Maui/Prism.Maui/Dialogs/DialogServiceBase.cs

@@ -195,7 +195,7 @@ public abstract class DialogServiceBase : IDialogService
                 };
             }
 
-            var view = dialogModal.DialogView;
+            var view = dialogModal.DialogView ?? throw new DialogException(DialogException.HostPageIsNotDialogHost);
             var dialogAware = GetDialogController(view);
 
             if (!dialogAware.CanCloseDialog())

src/Maui/Prism.Maui/Dialogs/IDialogContainer.cs

@@ -22,12 +22,12 @@ public interface IDialogContainer
     /// <summary>
     /// Gets the view associated with the currently displayed dialog.
     /// </summary>
-    View DialogView { get; }
+    View? DialogView { get; }
 
     /// <summary>
     /// Gets a command that can be used to dismiss the currently displayed dialog.
     /// </summary>
-    ICommand Dismiss { get; }
+    ICommand? Dismiss { get; }
 
     /// <summary>
     /// Configures the layout and behavior of the dialog.

src/Maui/Prism.Maui/Ioc/ContainerProvider.cs

@@ -1,4 +1,6 @@
 #nullable enable
+using System.Diagnostics.CodeAnalysis;
+
 namespace Prism.IoC;
 
 /// <summary>
@@ -53,6 +55,7 @@ public class ContainerProvider<T>
     /// Resolves the specified type from the Application's Container
     /// </summary>
     /// <param name="containerProvider"></param>
+    [return: MaybeNull]
     public static implicit operator T(ContainerProvider<T> containerProvider)
     {
         var container = ContainerLocator.Container;

src/Prism.Core/Common/IParameters.cs

@@ -6,14 +6,14 @@ namespace Prism.Common
     /// <summary>
     /// Defines a contract for specifying values associated with a unique key.
     /// </summary>
-    public interface IParameters : IEnumerable<KeyValuePair<string, object>>
+    public interface IParameters : IEnumerable<KeyValuePair<string, object?>>
     {
         /// <summary>
         /// Adds the specified key and value to the parameter collection.
         /// </summary>
         /// <param name="key">The key of the parameter to add.</param>
         /// <param name="value">The value of the parameter to add.</param>
-        void Add(string key, object value);
+        void Add(string key, object? value);
 
         /// <summary>
         /// Determines whether the <see cref="IParameters"/> contains the specified <paramref name="key"/>.
@@ -38,6 +38,7 @@ namespace Prism.Common
         /// <typeparam name="T">The type of the parameter to get.</typeparam>
         /// <param name="key">The key of the parameter to find.</param>
         /// <returns>A matching value of <typeparamref name="T"/> if it exists.</returns>
+        [return: MaybeNull]
         T GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(string key);
 
         /// <summary>

src/Prism.Core/Common/ParametersBase.cs

@@ -104,7 +104,7 @@ namespace Prism.Common
         /// </summary>
         /// <param name="key">The key to reference this value in the parameters collection.</param>
         /// <param name="value">The value of the parameter to store.</param>
-        public void Add(string key, object value) =>
+        public void Add(string key, object? value) =>
             _entries.Add(new KeyValuePair<string, object?>(key, value));
 
         /// <summary>
@@ -128,6 +128,7 @@ namespace Prism.Common
         /// <typeparam name="T">The type of object to be returned.</typeparam>
         /// <param name="key">The key for the value to be returned.</param>
         /// <returns>Returns a matching parameter of <typeparamref name="T"/> if one exists in the Collection.</returns>
+        [return: MaybeNull]
         public T GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(string key) =>
             _entries.GetValue<T>(key);
 

src/Prism.Core/Common/ParametersExtensions.cs

@@ -21,8 +21,9 @@ namespace Prism.Common
         /// <param name="key">The key of the parameter to find</param>
         /// <returns>A matching value of <typeparamref name="T"/> if it exists</returns>
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public static T GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object>> parameters, string key) =>
-            (T)GetValue(parameters, key, typeof(T));
+        [return: MaybeNull]
+        public static T GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object?>> parameters, string key) =>
+            (T?)GetValue(parameters, key, typeof(T));
 
         /// <summary>
         /// Searches <paramref name="parameters"/> for value referenced by <paramref name="key"/>
@@ -33,7 +34,7 @@ namespace Prism.Common
         /// <returns>A matching value of <paramref name="type"/> if it exists</returns>
         /// <exception cref="InvalidCastException">Unable to convert the value of Type</exception>
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public static object GetValue(this IEnumerable<KeyValuePair<string, object>> parameters, string key, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type type)
+        public static object? GetValue(this IEnumerable<KeyValuePair<string, object?>> parameters, string key, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type type)
         {
             foreach (var kvp in parameters)
             {
@@ -42,7 +43,7 @@ namespace Prism.Common
                     if (TryGetValueInternal(kvp, type, out var value))
                         return value;
 
-                    throw new InvalidCastException($"Unable to convert the value of Type '{kvp.Value.GetType().FullName}' to '{type.FullName}' for the key '{key}' ");
+                    throw new InvalidCastException($"Unable to convert the value of Type '{kvp.Value?.GetType().FullName ?? "null"}' to '{type.FullName}' for the key '{key}' ");
                 }
             }
 
@@ -58,7 +59,7 @@ namespace Prism.Common
         /// <param name="value">The value of parameter to return</param>
         /// <returns>Success if value is found; otherwise returns <c>false</c></returns>
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public static bool TryGetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object>> parameters, string key, out T value)
+        public static bool TryGetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object?>> parameters, string key, [MaybeNullWhen(false)] out T value)
         {
             var type = typeof(T);
 
@@ -87,7 +88,7 @@ namespace Prism.Common
         /// <param name="key">The key of the parameter to find</param>
         /// <returns>An IEnumerable{T} of all the values referenced by key</returns>
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public static IEnumerable<T> GetValues<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object>> parameters, string key)
+        public static IEnumerable<T> GetValues<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(this IEnumerable<KeyValuePair<string, object?>> parameters, string key)
         {
             List<T> values = [];
             var type = typeof(T);
@@ -105,7 +106,7 @@ namespace Prism.Common
             return values.ToArray();
         }
 
-        private static bool TryGetValueInternal(KeyValuePair<string, object> kvp, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type type, out object value)
+        private static bool TryGetValueInternal(KeyValuePair<string, object?> kvp, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type type, out object? value)
         {
             value = GetDefault(type);
             var valueAsString = kvp.Value is string str ? str : kvp.Value?.ToString();
@@ -154,7 +155,7 @@ namespace Prism.Common
         /// <param name="key">The key to search the <paramref name="parameters"/> for existence</param>
         /// <returns><c>true</c> if key exists; <c>false</c> otherwise</returns>
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public static bool ContainsKey(this IEnumerable<KeyValuePair<string, object>> parameters, string key) =>
+        public static bool ContainsKey(this IEnumerable<KeyValuePair<string, object?>> parameters, string key) =>
             parameters.Any(x => string.Compare(x.Key, key, StringComparison.Ordinal) == 0);
 
         private static object? GetDefault([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type type) => type.IsValueType ? Activator.CreateInstance(type) : null;

src/Prism.Core/Common/UriParsingHelper.cs

@@ -74,7 +74,7 @@ namespace Prism.Common
 
             if (parameters is not null)
             {
-                foreach (KeyValuePair<string, object> navigationParameter in parameters)
+                foreach (var navigationParameter in parameters)
                 {
                     navParameters.Add(navigationParameter.Key, navigationParameter.Value);
                 }
@@ -116,7 +116,7 @@ namespace Prism.Common
 
             if (parameters != null)
             {
-                foreach (KeyValuePair<string, object> navigationParameter in parameters)
+                foreach (var navigationParameter in parameters)
                 {
                     dialogParameters.Add(navigationParameter.Key, navigationParameter.Value);
                 }

src/Prism.Core/Mvvm/ErrorsContainer.cs

@@ -135,7 +135,7 @@ namespace Prism.Mvvm
 
             if (hasCurrentValidationResults || hasNewValidationResults)
             {
-                if (hasNewValidationResults)
+                if (newValidationResults is not null && hasNewValidationResults)
                 {
                     this.validationResults[localPropertyName] = new List<T>(newValidationResults);
                     this.raiseErrorsChanged(localPropertyName);

src/Prism.Core/Mvvm/PropertySupport.cs

@@ -54,6 +54,9 @@ namespace Prism.Mvvm
                 throw new ArgumentException(Resources.PropertySupport_ExpressionNotProperty_Exception, nameof(expression));
 
             var getMethod = property.GetMethod;
+            if (getMethod == null)
+                throw new ArgumentException(Resources.PropertySupport_ExpressionNotProperty_Exception, nameof(expression));
+
             if (getMethod.IsStatic)
                 throw new ArgumentException(Resources.PropertySupport_StaticExpression_Exception, nameof(expression));
 

src/Prism.Core/Mvvm/ViewRegistryBase{TBaseView}.cs

@@ -129,7 +129,7 @@ public abstract class ViewRegistryBase<TBaseView> : IViewRegistry
 
             return candidates
                 .Select(x => Type.GetType(x, false))
-                .Where(x => x is not null);
+                .OfType<Type>();
         }
 
         return [];

src/Prism.Core/Navigation/INavigationParametersInternal.cs

@@ -27,5 +27,6 @@ public interface INavigationParametersInternal
     /// <typeparam name="T">The type of object to be returned</typeparam>
     /// <param name="key">The key for the value to be returned</param>
     /// <returns>Returns a matching parameter of <typeparamref name="T"/> if one exists in the Collection</returns>
+    [return: MaybeNull]
     T GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(string key);
 }

src/Prism.Core/Navigation/NavigationParameters.cs

@@ -41,6 +41,7 @@ public class NavigationParameters : ParametersBase, INavigationParameters, INavi
         return _internalParameters.ContainsKey(key);
     }
 
+    [return: MaybeNull]
     T INavigationParametersInternal.GetValue<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(string key)
     {
         return _internalParameters.GetValue<T>(key);

src/Uno/Prism.Uno/Dialogs/DialogService.cs

@@ -28,13 +28,17 @@ namespace Prism.Dialogs
                 var dialogWindow = CreateDialogWindow(windowName);
                 if (dialogWindow is ContentDialog contentDialog)
                 {
-                    contentDialog.XamlRoot = _containerProvider.Resolve<Window>().Content.XamlRoot;
+                    var windowContent = _containerProvider.Resolve<Window>().Content;
+                    if (windowContent is null)
+                        throw new InvalidOperationException("A dialog requires a window with content.");
+
+                    contentDialog.XamlRoot = windowContent.XamlRoot;
                 }
                 ConfigureDialogWindowEvents(dialogWindow, callback);
                 ConfigureDialogWindowContent(name, dialogWindow, parameters);
 
                 var placement = parameters.ContainsKey(KnownDialogParameters.DialogPlacement) ?
-                    (parameters[KnownDialogParameters.DialogPlacement] is ContentDialogPlacement placementValue ? placementValue : Enum.Parse<ContentDialogPlacement>(parameters[KnownDialogParameters.DialogPlacement].ToString() ?? string.Empty)) : ContentDialogPlacement.Popup;
+                    (parameters[KnownDialogParameters.DialogPlacement] is ContentDialogPlacement placementValue ? placementValue : Enum.Parse<ContentDialogPlacement>(parameters[KnownDialogParameters.DialogPlacement]?.ToString() ?? string.Empty)) : ContentDialogPlacement.Popup;
 
                 await dialogWindow.ShowAsync(placement);
             }

tests/Maui/Prism.Maui.Tests/Fixtures/Common/UriParsingHelperFixture.cs

@@ -4,6 +4,23 @@ namespace Prism.Maui.Tests.Fixtures.Common;
 #nullable enable
 public class UriParsingHelperFixture
 {
+    [Fact]
+    public void SegmentCopiesPreserveExplicitNullNavigationAndDialogParameters()
+    {
+        INavigationParameters navigation = new NavigationParameters();
+        navigation.Add("value", null);
+        IDialogParameters dialog = new Prism.Dialogs.DialogParameters();
+        dialog.Add("value", null);
+
+        var navigationCopy = UriParsingHelper.GetSegmentParameters("Page", navigation);
+        var dialogCopy = UriParsingHelper.GetSegmentParameters("Dialog", dialog);
+
+        Assert.True(navigationCopy.ContainsKey("value"));
+        Assert.Null(Assert.Single(navigationCopy).Value);
+        Assert.True(dialogCopy.ContainsKey("value"));
+        Assert.Null(Assert.Single(dialogCopy).Value);
+    }
+
     const string _relativeUri = "MainPage?id=3&name=dan";
     const string _absoluteUriWithOutProtocol = "/MainPage?id=3&name=dan";
     const string _absoluteUri = "htp://www.dansiegel.net/MainPage?id=3&name=dan";

tests/Maui/Prism.Maui.Tests/Fixtures/Dialogs/DialogContainerLayoutFixture.cs

@@ -9,6 +9,25 @@ namespace Prism.Maui.Tests.Fixtures.Dialogs;
 
 public class DialogContainerLayoutFixture
 {
+    [Fact]
+    public void UnconfiguredContainerHasNoDialogOrDismissCommand()
+    {
+        IDialogContainer container = new DialogContainerPage();
+
+        Assert.Null(container.DialogView);
+        Assert.Null(container.Dismiss);
+    }
+
+    [Fact]
+    public void UnparentedPageUsesDefaultOverlayStyle()
+    {
+        var overlay = new LayoutContainer().CreateLayout(new ContentView(), false, new Command(() => { }));
+
+        var mask = Assert.IsType<BoxView>(overlay.Children[0]);
+        Assert.NotNull(mask.Style);
+        Assert.Contains(mask.Style.Setters, setter => setter.Property == BoxView.OpacityProperty && Equals(setter.Value, 0.75));
+    }
+
     [Fact]
     public void MaskCoversSafeAreaWithoutChangingPopupPositioning()
     {

tests/Prism.Core.Tests/Common/ParametersFixture.cs

@@ -7,6 +7,21 @@ namespace Prism.Tests.Common
 {
     public class ParametersFixture
     {
+        [Fact]
+        public void InterfaceEnumerationPreservesExplicitNullValues()
+        {
+            IParameters parameters = new MockParameters();
+            parameters.Add("value", null);
+
+            var entry = Assert.Single(parameters);
+            Assert.Equal("value", entry.Key);
+            Assert.Null(entry.Value);
+            Assert.True(parameters.ContainsKey("value"));
+            Assert.Null(parameters.GetValue<string>("value"));
+            Assert.False(parameters.TryGetValue<string>("value", out var value));
+            Assert.Null(value);
+        }
+
         [Fact]
         public void TryGetValueOfT()
         {
@@ -60,10 +75,10 @@ namespace Prism.Tests.Common
         {
             IParameters parameters = new MockParameters();
             if (addNullParameter)
-                parameters.Add("value", null!);
+                parameters.Add("value", null);
 
             Assert.Equal(42, parameters.GetValue<MockStructWithParameterlessConstructor>("value").Value);
-            Assert.Equal(42, ((MockStructWithParameterlessConstructor)parameters.GetValue("value", typeof(MockStructWithParameterlessConstructor))).Value);
+            Assert.Equal(42, Assert.IsType<MockStructWithParameterlessConstructor>(parameters.GetValue("value", typeof(MockStructWithParameterlessConstructor))).Value);
         }
 
         [Theory]
@@ -73,7 +88,7 @@ namespace Prism.Tests.Common
         {
             IParameters parameters = new MockParameters();
             if (addNullParameter)
-                parameters.Add("value", null!);
+                parameters.Add("value", null);
 
             var success = parameters.TryGetValue<MockStructWithParameterlessConstructor>("value", out var value);
 
@@ -85,7 +100,7 @@ namespace Prism.Tests.Common
         public void GetValuesRunsStructParameterlessConstructorForNullParameter()
         {
             IParameters parameters = new MockParameters();
-            parameters.Add("value", null!);
+            parameters.Add("value", null);
 
             var value = Assert.Single(parameters.GetValues<MockStructWithParameterlessConstructor>("value"));
 
@@ -100,7 +115,7 @@ namespace Prism.Tests.Common
         {
             IParameters parameters = new MockParameters();
             if (addNullParameter)
-                parameters.Add("value", null!);
+                parameters.Add("value", null);
 
             Assert.Null(parameters.GetValue<MockStructWithParameterlessConstructor?>("value"));
             Assert.Null(parameters.GetValue("value", typeof(MockStructWithParameterlessConstructor?)));