Merge pull request #6140 from workgroupengineering/fixes/application_some_nullable_warnings

fixes(Application): some nullable warnings

src/Avalonia.Controls/Application.cs

@@ -13,6 +13,7 @@ using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.Threading;
+#nullable enable
 
 namespace Avalonia
 {
@@ -35,27 +36,27 @@ namespace Avalonia
         /// <summary>
         /// The application-global data templates.
         /// </summary>
-        private DataTemplates _dataTemplates;
+        private DataTemplates? _dataTemplates;
 
         private readonly Lazy<IClipboard> _clipboard =
             new Lazy<IClipboard>(() => (IClipboard)AvaloniaLocator.Current.GetService(typeof(IClipboard)));
         private readonly Styler _styler = new Styler();
-        private Styles _styles;
-        private IResourceDictionary _resources;
+        private Styles? _styles;
+        private IResourceDictionary? _resources;
         private bool _notifyingResourcesChanged;
-        private Action<IReadOnlyList<IStyle>> _stylesAdded;
-        private Action<IReadOnlyList<IStyle>> _stylesRemoved;
+        private Action<IReadOnlyList<IStyle>>? _stylesAdded;
+        private Action<IReadOnlyList<IStyle>>? _stylesRemoved;
 
         /// <summary>
         /// Defines the <see cref="DataContext"/> property.
         /// </summary>
-        public static readonly StyledProperty<object> DataContextProperty =
+        public static readonly StyledProperty<object?> DataContextProperty =
             StyledElement.DataContextProperty.AddOwner<Application>();
 
         /// <inheritdoc/>
-        public event EventHandler<ResourcesChangedEventArgs> ResourcesChanged;
+        public event EventHandler<ResourcesChangedEventArgs>? ResourcesChanged;
 
-        public event EventHandler<UrlOpenedEventArgs> UrlsOpened; 
+        public event EventHandler<UrlOpenedEventArgs>? UrlsOpened; 
 
         /// <summary>
         /// Creates an instance of the <see cref="Application"/> class.
@@ -72,7 +73,7 @@ namespace Avalonia
         /// The data context property specifies the default object that will
         /// be used for data binding.
         /// </remarks>
-        public object DataContext
+        public object? DataContext
         {
             get { return GetValue(DataContextProperty); }
             set { SetValue(DataContextProperty, value); }
@@ -162,7 +163,7 @@ namespace Avalonia
         /// <summary>
         /// Gets the styling parent of the application, which is null.
         /// </summary>
-        IStyleHost IStyleHost.StylingParent => null;
+        IStyleHost? IStyleHost.StylingParent => null;
 
         /// <inheritdoc/>
         bool IStyleHost.IsStylesInitialized => _styles != null;
@@ -194,7 +195,7 @@ namespace Avalonia
         public virtual void Initialize() { }
 
         /// <inheritdoc/>
-        bool IResourceNode.TryGetResource(object key, out object value)
+        bool IResourceNode.TryGetResource(object key, out object? value)
         {
             value = null;
             return (_resources?.TryGetResource(key, out value) ?? false) ||
@@ -279,17 +280,17 @@ namespace Avalonia
             NotifyResourcesChanged(e);
         }
 
-        private string _name;
+        private string? _name;
         /// <summary>
         /// Defines Name property
         /// </summary>
-        public static readonly DirectProperty<Application, string> NameProperty =
-            AvaloniaProperty.RegisterDirect<Application, string>("Name", o => o.Name, (o, v) => o.Name = v);
+        public static readonly DirectProperty<Application, string?> NameProperty =
+            AvaloniaProperty.RegisterDirect<Application, string?>("Name", o => o.Name, (o, v) => o.Name = v);
 
         /// <summary>
         /// Application name to be used for various platform-specific purposes
         /// </summary>
-        public string Name
+        public string? Name
         {
             get => _name;
             set => SetAndRaise(NameProperty, ref _name, value);