chore: enable nullability for core mvvm

src/Prism.Core/Mvvm/BindableBase.cs

@@ -1,8 +1,7 @@
-using System;
-using System.Collections.Generic;
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 
+#nullable enable
 namespace Prism.Mvvm
 {
     /// <summary>
@@ -13,7 +12,7 @@ public abstract class BindableBase : INotifyPropertyChanged
         /// <summary>
         /// Occurs when a property value changes.
         /// </summary>
-        public event PropertyChangedEventHandler PropertyChanged;
+        public event PropertyChangedEventHandler? PropertyChanged;
 
         /// <summary>
         /// Checks if a property already matches a desired value. Sets the property and
@@ -27,7 +26,7 @@ public abstract class BindableBase : INotifyPropertyChanged
         /// support CallerMemberName.</param>
         /// <returns>True if the value was changed, false if the existing value matched the
         /// desired value.</returns>
-        protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
+        protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string? propertyName = null)
         {
             if (EqualityComparer<T>.Default.Equals(storage, value)) return false;
 
@@ -50,7 +49,8 @@ protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName]
         /// <param name="onChanged">Action that is called after the property value has been changed.</param>
         /// <returns>True if the value was changed, false if the existing value matched the
         /// desired value.</returns>
-        protected virtual bool SetProperty<T>(ref T storage, T value, Action onChanged, [CallerMemberName] string propertyName = null)
+        protected virtual bool SetProperty<T>(ref T storage, T value, Action? onChanged,
+            [CallerMemberName] string? propertyName = null)
         {
             if (EqualityComparer<T>.Default.Equals(storage, value)) return false;
 
@@ -67,7 +67,7 @@ protected virtual bool SetProperty<T>(ref T storage, T value, Action onChanged,
         /// <param name="propertyName">Name of the property used to notify listeners. This
         /// value is optional and can be provided automatically when invoked from compilers
         /// that support <see cref="CallerMemberNameAttribute"/>.</param>
-        protected void RaisePropertyChanged([CallerMemberName] string propertyName = null)
+        protected void RaisePropertyChanged([CallerMemberName] string? propertyName = null)
         {
             OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
         }

src/Prism.Core/Mvvm/ErrorsContainer.cs

@@ -1,8 +1,6 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Linq.Expressions;
 
+#nullable enable
 namespace Prism.Mvvm
 {
     /// <summary>
@@ -53,10 +51,7 @@ public bool HasErrors
         /// Returns all the errors in the container.
         /// </summary>
         /// <returns>The dictionary of errors per property.</returns>
-        public Dictionary<string, List<T>> GetErrors()
-        {
-            return validationResults;
-        }
+        public Dictionary<string, List<T>> GetErrors() => validationResults;
 
         /// <summary>
         /// Gets the validation errors for a specified property.
@@ -65,9 +60,8 @@ public Dictionary<string, List<T>> GetErrors()
         /// <returns>The validation errors of type <typeparamref name="T"/> for the property.</returns>
         public IEnumerable<T> GetErrors(string propertyName)
         {
-            var localPropertyName = propertyName ?? string.Empty;
-            List<T> currentValidationResults = null;
-            if (this.validationResults.TryGetValue(localPropertyName, out currentValidationResults))
+            var localPropertyName = propertyName;
+            if (this.validationResults.TryGetValue(localPropertyName, out var currentValidationResults))
             {
                 return currentValidationResults;
             }
@@ -110,10 +104,7 @@ public void ClearErrors<TProperty>(Expression<Func<TProperty>> propertyExpressio
         /// <example>
         /// container.ClearErrors("SomeProperty");
         /// </example>
-        public void ClearErrors(string propertyName)
-        {
-            this.SetErrors(propertyName, new List<T>());
-        }
+        public void ClearErrors(string propertyName) => this.SetErrors(propertyName, new List<T>());
 
         /// <summary>
         /// Sets the validation errors for the specified property.
@@ -140,7 +131,7 @@ public void SetErrors(string propertyName, IEnumerable<T> newValidationResults)
         {
             var localPropertyName = propertyName ?? string.Empty;
             var hasCurrentValidationResults = this.validationResults.ContainsKey(localPropertyName);
-            var hasNewValidationResults = newValidationResults != null && newValidationResults.Count() > 0;
+            var hasNewValidationResults = newValidationResults.Count() > 0;
 
             if (hasCurrentValidationResults || hasNewValidationResults)
             {

src/Prism.Core/Mvvm/IViewRegistry.cs

@@ -1,8 +1,4 @@
-using System;
-using System.Collections.Generic;
-using Prism.Ioc;
-
-namespace Prism.Mvvm;
+namespace Prism.Mvvm;
 
 /// <summary>
 /// Provides an abstraction layer for ViewRegistration that can be mocked

src/Prism.Core/Mvvm/PropertySupport.cs

@@ -1,10 +1,8 @@
-
-
-using System;
 using System.Linq.Expressions;
 using System.Reflection;
 using Prism.Properties;
 
+#nullable enable
 namespace Prism.Mvvm
 {
     ///<summary>

src/Prism.Core/Mvvm/ViewCreationException.cs

@@ -1,5 +1,4 @@
-using System;
-
+#nullable enable
 namespace Prism.Mvvm;
 
 /// <summary>
@@ -23,7 +22,7 @@ public ViewCreationException(string viewName, ViewType viewType)
     /// <param name="viewName">The name of the view that failed to create.</param>
     /// <param name="viewType">The type of view that failed to create (Page, Region, or Dialog).</param>
     /// <param name="innerException">The inner exception that caused the view creation to fail.</param>
-    public ViewCreationException(string viewName, ViewType viewType, Exception innerException)
+    public ViewCreationException(string viewName, ViewType viewType, Exception? innerException)
         : base($"Unable to create {viewType} '{viewName}'.", innerException)
     {
         ViewName = viewName;

src/Prism.Core/Mvvm/ViewModelCreationException.cs

@@ -1,14 +1,14 @@
-using System;
-using System.ComponentModel;
+using System.ComponentModel;
 
+#nullable enable
 namespace Prism.Mvvm;
 
 /// <summary>
 /// Exception thrown when an error occurs during ViewModel creation.
 /// </summary>
 public class ViewModelCreationException : Exception
 {
-    private static Func<object, string> _viewNameDelegate = null;
+    private static Func<object, string>? _viewNameDelegate;
 
     /// <summary>
     /// Gets the name of the view associated with the exception, based on platform-specific logic.

src/Prism.Core/Mvvm/ViewModelLocationProvider.cs

@@ -1,12 +1,9 @@
-
-
-using System;
-using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Reflection;
 
+#nullable enable
 namespace Prism.Mvvm
 {
     /// <summary>
@@ -52,24 +49,24 @@ public static void Reset()
         /// <summary>
         /// ViewModelFactory that provides the View instance and ViewModel type as parameters.
         /// </summary>
-        static Func<object, Type, object> _defaultViewModelFactoryWithViewParameter;
+        static Func<object, Type, object>? _defaultViewModelFactoryWithViewParameter;
 
         /// <summary>
         /// Default view type to view model type resolver, assumes the view model is in same assembly as the view type, but in the "ViewModels" namespace.
         /// </summary>
-        static Func<Type, Type> _defaultViewTypeToViewModelTypeResolver = DefaultViewTypeToViewModel;
+        static Func<Type, Type?> _defaultViewTypeToViewModelTypeResolver = DefaultViewTypeToViewModel;
 
-        private static Type DefaultViewTypeToViewModel(Type viewType)
+        private static Type? DefaultViewTypeToViewModel(Type viewType)
         {
             var viewName = viewType.FullName;
-            viewName = viewName.Replace(".Views.", ".ViewModels.");
+            viewName = viewName?.Replace(".Views.", ".ViewModels.");
             var viewAssemblyName = viewType.GetTypeInfo().Assembly.FullName;
-            var suffix = viewName.EndsWith("View") ? "Model" : "ViewModel";
+            var suffix = viewName != null && viewName.EndsWith("View") ? "Model" : "ViewModel";
             var viewModelName = string.Format(CultureInfo.InvariantCulture, "{0}{1}, {2}", viewName, suffix, viewAssemblyName);
             return Type.GetType(viewModelName);
         }
 
-        static Func<object, Type> _defaultViewToViewModelTypeResolver = view => null;
+        static Func<object, Type?> _defaultViewToViewModelTypeResolver = view => null;
 
         /// <summary>
         /// Sets the default view model factory.
@@ -93,7 +90,7 @@ public static void SetDefaultViewModelFactory(Func<object, Type, object> viewMod
         /// Sets the default view type to view model type resolver.
         /// </summary>
         /// <param name="viewTypeToViewModelTypeResolver">The view type to view model type resolver.</param>
-        public static void SetDefaultViewTypeToViewModelTypeResolver(Func<Type, Type> viewTypeToViewModelTypeResolver)
+        public static void SetDefaultViewTypeToViewModelTypeResolver(Func<Type, Type?> viewTypeToViewModelTypeResolver)
         {
             _defaultViewTypeToViewModelTypeResolver = viewTypeToViewModelTypeResolver;
         }
@@ -102,7 +99,7 @@ public static void SetDefaultViewTypeToViewModelTypeResolver(Func<Type, Type> vi
         /// Sets the default ViewModel Type Resolver given the View instance. This can be used to evaluate the View for
         /// custom attributes or Attached Properties to determine the ViewModel Type.
         /// </summary> 
-        public static void SetDefaultViewToViewModelTypeResolver(Func<object, Type> viewToViewModelTypeResolver) =>
+        public static void SetDefaultViewToViewModelTypeResolver(Func<object, Type?> viewToViewModelTypeResolver) =>
             _defaultViewToViewModelTypeResolver = viewToViewModelTypeResolver;
 
         /// <summary>
@@ -114,7 +111,7 @@ public static void SetDefaultViewToViewModelTypeResolver(Func<object, Type> view
         public static void AutoWireViewModelChanged(object view, Action<object, object> setDataContextCallback)
         {
             // Try mappings first
-            object viewModel = GetViewModelForView(view);
+            object? viewModel = GetViewModelForView(view);
 
             // try to use ViewModel type
             if (viewModel == null)
@@ -144,30 +141,24 @@ public static void AutoWireViewModelChanged(object view, Action<object, object>
         /// </summary>
         /// <param name="view">The view that the view model wants.</param>
         /// <returns>The ViewModel that corresponds to the view passed as a parameter.</returns>
-        private static object GetViewModelForView(object view)
+        private static object? GetViewModelForView(object view)
         {
             var viewKey = view.GetType().ToString();
 
             // Mapping of view models base on view type (or instance) goes here
-            if (_factories.ContainsKey(viewKey))
-                return _factories[viewKey]();
-
-            return null;
+            return _factories.ContainsKey(viewKey) ? _factories[viewKey]() : null;
         }
 
         /// <summary>
         /// Gets the ViewModel type for the specified view.
         /// </summary>
         /// <param name="view">The View that the ViewModel wants.</param>
         /// <returns>The ViewModel type that corresponds to the View.</returns>
-        private static Type GetViewModelTypeForView(Type view)
+        private static Type? GetViewModelTypeForView(Type view)
         {
             var viewKey = view.ToString();
 
-            if (_typeFactories.ContainsKey(viewKey))
-                return _typeFactories[viewKey];
-
-            return null;
+            return _typeFactories.ContainsKey(viewKey) ? _typeFactories[viewKey] : null;
         }
 
         /// <summary>

src/Prism.Core/Mvvm/ViewRegistration.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Prism.Mvvm;
+namespace Prism.Mvvm;
 
 /// <summary>
 /// Represents information about a registered view.