Enable nullable on Avalonia.Android project (#15331)

* Enable nullable on Avalonia.Android project

* More specific exception

src/Android/Avalonia.Android/AndroidInputMethod.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Android.Content;
 using Android.Runtime;
 using Android.Text;
@@ -13,8 +14,9 @@ namespace Avalonia.Android
     {
         public View View { get; }
 
-        public TextInputMethodClient Client { get; }
+        public TextInputMethodClient? Client { get; }
 
+        [MemberNotNullWhen(true, nameof(Client))]
         public bool IsActive { get; }
 
         public InputMethodManager IMM { get; }
@@ -38,8 +40,8 @@ namespace Avalonia.Android
     {
         private readonly TView _host;
         private readonly InputMethodManager _imm;
-        private TextInputMethodClient _client;
+        private TextInputMethodClient? _client;
-        private AvaloniaInputConnection _inputConnection;
+        private AvaloniaInputConnection? _inputConnection;
 
         public AndroidInputMethod(TView host)
         {
@@ -47,7 +49,8 @@ namespace Avalonia.Android
                 throw new InvalidOperationException("Host should return true from OnCheckIsTextEditor()");
 
             _host = host;
-            _imm = host.Context.GetSystemService(Context.InputMethodService).JavaCast<InputMethodManager>();
+            _imm = host.Context?.GetSystemService(Context.InputMethodService).JavaCast<InputMethodManager>()
+                   ?? throw new InvalidOperationException("Context.InputMethodService is expected to be not null.");
 
             _host.Focusable = true;
             _host.FocusableInTouchMode = true;
@@ -55,9 +58,11 @@ namespace Avalonia.Android
 
         public View View => _host;
 
+        [MemberNotNullWhen(true, nameof(Client))]
+        [MemberNotNullWhen(true, nameof(_client))]
         public bool IsActive => Client != null;
 
-        public TextInputMethodClient Client => _client;
+        public TextInputMethodClient? Client => _client;
 
         public InputMethodManager IMM => _imm;
 
@@ -66,7 +71,7 @@ namespace Avalonia.Android
 
         }
 
-        public void SetClient(TextInputMethodClient client)
+        public void SetClient(TextInputMethodClient? client)
         {
             _client = client;
 
@@ -103,9 +108,9 @@ namespace Avalonia.Android
             }
         }
 
-        private void _client_SelectionChanged(object sender, EventArgs e)
+        private void _client_SelectionChanged(object? sender, EventArgs e)
         {
-            if (_inputConnection.IsInBatchEdit)
+            if (_inputConnection is null || _inputConnection.IsInBatchEdit)
                 return;
             OnSelectionChanged();
         }
@@ -121,19 +126,19 @@ namespace Avalonia.Android
 
             _imm.UpdateSelection(_host, selection.Start, selection.End, selection.Start, selection.End);
 
-            _inputConnection.SetSelection(selection.Start, selection.End);
+            _inputConnection?.SetSelection(selection.Start, selection.End);
         }
 
-        private void _client_SurroundingTextChanged(object sender, EventArgs e)
+        private void _client_SurroundingTextChanged(object? sender, EventArgs e)
         {
-            if (_inputConnection.IsInBatchEdit)
+            if (_inputConnection is null || _inputConnection.IsInBatchEdit)
                 return;
             OnSurroundingTextChanged();
         }
 
         public void OnBatchEditedEnded()
         {
-            if (_inputConnection.IsInBatchEdit)
+            if (_inputConnection is null || _inputConnection.IsInBatchEdit)
                 return;
 
             OnSurroundingTextChanged();
@@ -142,7 +147,7 @@ namespace Avalonia.Android
 
         private void OnSurroundingTextChanged()
         {
-            if(_client is null)
+            if(_client is null || _inputConnection is null)
             {
                 return;
             }
@@ -199,7 +204,7 @@ namespace Avalonia.Android
             _host.InitEditorInfo((topLevel, outAttrs) =>
             {
                 if (_client == null)
-                    return null;
+                    return null!;
 
                 _inputConnection = new AvaloniaInputConnection(topLevel, this);
 

src/Android/Avalonia.Android/AndroidPlatform.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using Avalonia.Controls;
 using Avalonia.Android;
 using Avalonia.Android.Platform;
 using Avalonia.Android.Platform.Input;
@@ -12,7 +11,6 @@ using Avalonia.OpenGL.Egl;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Rendering.Composition;
-using Avalonia.OpenGL;
 
 namespace Avalonia
 {
@@ -66,9 +64,9 @@ namespace Avalonia.Android
     class AndroidPlatform
     {
         public static readonly AndroidPlatform Instance = new AndroidPlatform();
-        public static AndroidPlatformOptions Options { get; private set; }
+        public static AndroidPlatformOptions? Options { get; private set; }
 
-        internal static Compositor Compositor { get; private set; }
+        internal static Compositor? Compositor { get; private set; }
 
         public static void Initialize()
         {
@@ -95,7 +93,7 @@ namespace Avalonia.Android
             AvaloniaLocator.CurrentMutable.Bind<Compositor>().ToConstant(Compositor);
         }
         
-        private static IPlatformGraphics InitializeGraphics(AndroidPlatformOptions opts)
+        private static IPlatformGraphics? InitializeGraphics(AndroidPlatformOptions opts)
         {
             if (opts.RenderingMode is null || !opts.RenderingMode.Any())
             {

src/Android/Avalonia.Android/AndroidRuntimePlatform.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 using Android.Content.PM;
 using Android.Content;
 using Avalonia.Platform;

src/Android/Avalonia.Android/AndroidThreadingInterface.cs

@@ -14,11 +14,12 @@ namespace Avalonia.Android
     internal sealed class AndroidThreadingInterface : IPlatformThreadingInterface
     {
         private Handler _handler;
-        private static Thread s_uiThread;
+        private static Thread? s_uiThread;
 
         public AndroidThreadingInterface()
         {
-            _handler = new Handler(App.Context.MainLooper);
+            _handler = new Handler(App.Context.MainLooper
+                ?? throw new InvalidOperationException("Application.Context.MainLooper was not expected to be null."));
         }
 
         public IDisposable StartTimer(DispatcherPriority priority, TimeSpan interval, Action tick)
@@ -27,7 +28,7 @@ namespace Avalonia.Android
                 interval = TimeSpan.FromMilliseconds(10);
 
             var stopped = false;
-            Timer timer = null;
+            Timer? timer = null;
             timer = new Timer(_ =>
             {
                 if (stopped)
@@ -42,7 +43,7 @@ namespace Avalonia.Android
                     finally
                     {
                         if (!stopped)
-                            timer.Change(interval, Timeout.InfiniteTimeSpan);
+                            timer!.Change(interval, Timeout.InfiniteTimeSpan);
                     }
                 });
             },
@@ -70,9 +71,9 @@ namespace Avalonia.Android
                     return s_uiThread == Thread.CurrentThread;
 
                 var isOnMainThread = OperatingSystem.IsAndroidVersionAtLeast(23)
-                    ? Looper.MainLooper.IsCurrentThread
+                    ? Looper.MainLooper?.IsCurrentThread
-                    : Looper.MainLooper.Thread.Equals(Java.Lang.Thread.CurrentThread());
+                    : Looper.MainLooper?.Thread.Equals(Java.Lang.Thread.CurrentThread());
-                if (isOnMainThread)
+                if (isOnMainThread == true)
                 {
                     s_uiThread = Thread.CurrentThread;
                     return true;
@@ -81,6 +82,6 @@ namespace Avalonia.Android
                 return false;
             }
         }
-        public event Action<DispatcherPriority?> Signaled;
+        public event Action<DispatcherPriority?>? Signaled;
     }
 }

src/Android/Avalonia.Android/AndroidViewControlHandle.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 
 using Android.Views;
 

src/Android/Avalonia.Android/Avalonia.Android.csproj

@@ -3,7 +3,6 @@
     <TargetFramework>$(AvsCurrentAndroidTargetFramework)</TargetFramework>
     <SupportedOSPlatformVersion>$(AvsMinSupportedAndroidVersion)</SupportedOSPlatformVersion>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <DebugType>portable</DebugType>
     <AndroidResgenNamespace>Avalonia.Android.Internal</AndroidResgenNamespace>
   </PropertyGroup>
   <ItemGroup>
@@ -16,6 +15,8 @@
     <ProjectReference Include="..\..\Avalonia.Base\Avalonia.Base.csproj" />
     <ProjectReference Include="..\..\Skia\Avalonia.Skia\Avalonia.Skia.csproj" />
   </ItemGroup>
+
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
+  <Import Project="..\..\..\build\NullableEnable.props" />
 </Project>

src/Android/Avalonia.Android/AvaloniaActivity.cs

@@ -1,4 +1,3 @@
-#nullable enable
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.Versioning;

src/Android/Avalonia.Android/AvaloniaMainActivity.App.cs

@@ -1,12 +1,4 @@
-#nullable enable
+namespace Avalonia.Android;
-
-using Android.OS;
-using Android.Views;
-using Avalonia.Android.Platform;
-using Avalonia.Controls.ApplicationLifetimes;
-using Avalonia.Platform;
-
-namespace Avalonia.Android;
 
 public class AvaloniaMainActivity<TApp> : AvaloniaMainActivity
     where TApp : Application, new()

src/Android/Avalonia.Android/AvaloniaMainActivity.cs

@@ -1,7 +1,4 @@
-#nullable enable
-
 using System;
-using System.Diagnostics.CodeAnalysis;
 using Android.OS;
 using Avalonia.Android.Platform;
 using Avalonia.Controls.ApplicationLifetimes;

src/Android/Avalonia.Android/AvaloniaView.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Android
         private EmbeddableControlRoot _root;
         private readonly ViewImpl _view;
 
-        private IDisposable _timerSubscription;
+        private IDisposable? _timerSubscription;
 
         public AvaloniaView(Context context) : base(context)
         {
@@ -35,9 +35,9 @@ namespace Avalonia.Android
         }
 
         internal TopLevelImpl TopLevelImpl => _view;
-        internal TopLevel TopLevel => _root;
+        internal TopLevel? TopLevel => _root;
 
-        public object Content
+        public object? Content
         {
             get { return _root.Content; }
             set { _root.Content = value; }
@@ -47,10 +47,10 @@ namespace Avalonia.Android
         {
             base.Dispose(disposing);
             _root?.Dispose();
-            _root = null;
+            _root = null!;
         }
 
-        public override bool DispatchKeyEvent(KeyEvent e)
+        public override bool DispatchKeyEvent(KeyEvent? e)
         {
             return _view.View.DispatchKeyEvent(e);
         }
@@ -91,7 +91,7 @@ namespace Avalonia.Android
             }
         }
         
-        protected override void OnConfigurationChanged(Configuration newConfig)
+        protected override void OnConfigurationChanged(Configuration? newConfig)
         {
             base.OnConfigurationChanged(newConfig);
             OnConfigurationChanged();
@@ -99,8 +99,12 @@ namespace Avalonia.Android
 
         private void OnConfigurationChanged()
         {
-            var settings = AvaloniaLocator.Current.GetRequiredService<IPlatformSettings>() as AndroidPlatformSettings;
+            if (Context is { } context)
-            settings?.OnViewConfigurationChanged(Context);
+            {
+                var settings =
+                    AvaloniaLocator.Current.GetRequiredService<IPlatformSettings>() as AndroidPlatformSettings;
+                settings?.OnViewConfigurationChanged(context);
+            }
         }
 
         class ViewImpl : TopLevelImpl
@@ -111,17 +115,11 @@ namespace Avalonia.Android
                 View.FocusChange += ViewImpl_FocusChange;
             }
 
-            private void ViewImpl_FocusChange(object sender, FocusChangeEventArgs e)
+            private void ViewImpl_FocusChange(object? sender, FocusChangeEventArgs e)
             {
                 if(!e.HasFocus)
                     LostFocus?.Invoke();
             }
-
-            protected override void OnResized(Size size)
-            {
-                MaxClientSize = size;
-                base.OnResized(size);
-            }
         }
     }
 }

src/Android/Avalonia.Android/ChoreographerTimer.cs

@@ -14,14 +14,14 @@ namespace Avalonia.Android
 {
     internal sealed class ChoreographerTimer : Java.Lang.Object, IRenderTimer, Choreographer.IFrameCallback
     {
-        private readonly object _lock = new object();
+        private readonly object _lock = new();
 
         private readonly Thread _thread;
-        private readonly TaskCompletionSource<Choreographer> _choreographer = new TaskCompletionSource<Choreographer>();
+        private readonly TaskCompletionSource<Choreographer> _choreographer = new();
 
         private readonly ISet<AvaloniaView> _views = new HashSet<AvaloniaView>();
 
-        private Action<TimeSpan> _tick;
+        private Action<TimeSpan>? _tick;
         private int _count;
 
         public ChoreographerTimer()
@@ -29,8 +29,7 @@ namespace Avalonia.Android
             _thread = new Thread(Loop);
             _thread.Start();
         }
-        
+
-        
         public bool RunsInBackground => true;
 
         public event Action<TimeSpan> Tick
@@ -84,7 +83,7 @@ namespace Avalonia.Android
         private void Loop()
         {
             Looper.Prepare();
-            _choreographer.SetResult(Choreographer.Instance);
+            _choreographer.SetResult(Choreographer.Instance!);
             Looper.Loop();
         }
 
@@ -96,7 +95,7 @@ namespace Avalonia.Android
             {
                 if (_count > 0 && _views.Count > 0)
                 {
-                    Choreographer.Instance.PostFrameCallback(this);
+                    Choreographer.Instance!.PostFrameCallback(this);
                 }
             }
         }

src/Android/Avalonia.Android/IActivityResultHandler.cs

@@ -3,12 +3,11 @@ using Android.App;
 using Android.Content;
 using Android.Content.PM;
 
-namespace Avalonia.Android
+namespace Avalonia.Android;
+
+public interface IActivityResultHandler
 {
-    public interface IActivityResultHandler
+    public Action<int, Result, Intent?>? ActivityResult { get; set; }
-    {
-        public Action<int, Result, Intent> ActivityResult { get; set; }
         
-        public Action<int, string[], Permission[]> RequestPermissionsResult { get; set; }
+    public Action<int, string[], Permission[]>? RequestPermissionsResult { get; set; }
-    }
 }

src/Android/Avalonia.Android/IAndroidNavigationService.cs

@@ -1,5 +1,4 @@
 using System;
-using Avalonia.Controls.ApplicationLifetimes;
 
 namespace Avalonia.Android
 {

src/Android/Avalonia.Android/IAvaloniaActivity.cs

@@ -1,5 +1,4 @@
-#nullable enable
+using System;
-using System;
 using Avalonia.Controls.ApplicationLifetimes;
 
 namespace Avalonia.Android;

src/Android/Avalonia.Android/Platform/AndroidActivatableLifetime.cs

@@ -6,9 +6,9 @@ namespace Avalonia.Android.Platform;
 
 internal class AndroidActivatableLifetime : IActivatableLifetime
 {
-    private IAvaloniaActivity _activity;
+    private IAvaloniaActivity? _activity;
 
-    public IAvaloniaActivity Activity
+    public IAvaloniaActivity? Activity
     {
         get => _activity;
         set
@@ -29,18 +29,18 @@ internal class AndroidActivatableLifetime : IActivatableLifetime
         }
     }
     
-    public event EventHandler<ActivatedEventArgs> Activated;
+    public event EventHandler<ActivatedEventArgs>? Activated;
-    public event EventHandler<ActivatedEventArgs> Deactivated;
+    public event EventHandler<ActivatedEventArgs>? Deactivated;
 
     public bool TryLeaveBackground() => false;
     public bool TryEnterBackground() => (_activity as Activity)?.MoveTaskToBack(true) == true;
 
-    private void ActivityOnDeactivated(object sender, ActivatedEventArgs e)
+    private void ActivityOnDeactivated(object? sender, ActivatedEventArgs e)
     {
         Deactivated?.Invoke(this, e);
     }
 
-    private void ActivityOnActivated(object sender, ActivatedEventArgs e)
+    private void ActivityOnActivated(object? sender, ActivatedEventArgs e)
     {
         Activated?.Invoke(this, e);
     }

src/Android/Avalonia.Android/Platform/AndroidInsetsManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Android.App;
 using Android.OS;
 using Android.Views;
 using Android.Views.Animations;
@@ -15,7 +16,7 @@ namespace Avalonia.Android.Platform
 {
     internal sealed class AndroidInsetsManager : WindowInsetsAnimationCompat.Callback, IInsetsManager, IOnApplyWindowInsetsListener, ViewTreeObserver.IOnGlobalLayoutListener, IInputPane
     {
-        private readonly AvaloniaMainActivity _activity;
+        private readonly Activity _activity;
         private readonly TopLevelImpl _topLevel;
         private bool _displayEdgeToEdge;
         private bool? _systemUiVisibility;
@@ -28,8 +29,8 @@ namespace Avalonia.Android.Platform
 
         private AndroidWindow Window => _activity.Window ?? throw new InvalidOperationException("Activity.Window must be set."); 
         
-        public event EventHandler<SafeAreaChangedArgs> SafeAreaChanged;
+        public event EventHandler<SafeAreaChangedArgs>? SafeAreaChanged;
-        public event EventHandler<InputPaneStateEventArgs> StateChanged;
+        public event EventHandler<InputPaneStateEventArgs>? StateChanged;
 
         public InputPaneState State
         {
@@ -73,7 +74,7 @@ namespace Avalonia.Android.Platform
             }
         }
 
-        internal AndroidInsetsManager(AvaloniaMainActivity activity, TopLevelImpl topLevel) : base(DispatchModeStop)
+        internal AndroidInsetsManager(Activity activity, TopLevelImpl topLevel) : base(DispatchModeStop)
         {
             _activity = activity;
             _topLevel = topLevel;
@@ -155,7 +156,7 @@ namespace Avalonia.Android.Platform
             Dispatcher.UIThread.Send(_ => SafeAreaChanged?.Invoke(this, new SafeAreaChangedArgs(safeAreaPadding)));
         }
         
-        private void NotifyStateChanged(InputPaneState newState, Rect? startRect, Rect endRect, TimeSpan animationDuration, IEasing easing)
+        private void NotifyStateChanged(InputPaneState newState, Rect? startRect, Rect endRect, TimeSpan animationDuration, IEasing? easing)
         {
             Dispatcher.UIThread.Send(_ => StateChanged?.Invoke(this, new InputPaneStateEventArgs(newState, startRect, endRect, animationDuration, easing)));
         }
@@ -300,7 +301,8 @@ namespace Avalonia.Android.Platform
                     var duration = TimeSpan.FromMilliseconds(animation.DurationMillis);
 
                     bool isOpening = State == InputPaneState.Open;
-                    NotifyStateChanged(State, isOpening ? upperRect : lowerRect, isOpening ? lowerRect : upperRect, duration, new AnimationEasing(animation.Interpolator));
+                    NotifyStateChanged(State, isOpening ? upperRect : lowerRect, isOpening ? lowerRect : upperRect, duration,
+                        animation.Interpolator is { } interpolator ? new AnimationEasing(interpolator) : null);
                 }
             }
 

src/Android/Avalonia.Android/Platform/AndroidNativeControlHostImpl.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 using System.Diagnostics.CodeAnalysis;
 
 using Android.Views;

src/Android/Avalonia.Android/Platform/AndroidPlatformSettings.cs

@@ -1,12 +1,7 @@
 using System;
-using Android;
 using Android.Content;
 using Android.Content.Res;
-using Android.Graphics;
 using Android.Provider;
-using Android.Views.Accessibility;
-using AndroidX.Core.Content.Resources;
-using Avalonia.Media;
 using Avalonia.Platform;
 using Color = Avalonia.Media.Color;
 
@@ -60,16 +55,25 @@ internal class AndroidPlatformSettings : DefaultPlatformSettings
         else if (OperatingSystem.IsAndroidVersionAtLeast(23))
         {
             // See https://developer.android.com/reference/android/R.attr
-            var array = context.Theme.ObtainStyledAttributes(new[] { 16843829 }); // Resource.Attribute.ColorAccent
+            var array = context.Theme?.ObtainStyledAttributes(new[] { 16843829 }); // Resource.Attribute.ColorAccent
-            var accent = array.GetColor(0, 0);
+            if (array is not null)
-
-            _latestValues = new PlatformColorValues
             {
-                ThemeVariant = systemTheme,
+                try
-                ContrastPreference = IsHighContrast(context),
+                {
-                AccentColor1 = new Color(accent.A, accent.R, accent.G, accent.B)
+                    var accent = array.GetColor(0, 0);
-            };
+
-            array.Recycle();
+                    _latestValues = new PlatformColorValues
+                    {
+                        ThemeVariant = systemTheme,
+                        ContrastPreference = IsHighContrast(context),
+                        AccentColor1 = new Color(accent.A, accent.R, accent.G, accent.B)
+                    };
+                }
+                finally
+                {
+                    array.Recycle();   
+                }
+            }
         }
         else
         {

src/Android/Avalonia.Android/Platform/AndroidSystemNavigationManager.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 using Avalonia.Interactivity;
 using Avalonia.Platform;
 

src/Android/Avalonia.Android/Platform/ClipboardImpl.cs

@@ -1,5 +1,3 @@
-#nullable enable
-
 using System;
 using System.Threading.Tasks;
 using Android.Content;

src/Android/Avalonia.Android/Platform/PlatformSupport.cs

@@ -2,7 +2,6 @@
 using System.Linq;
 using System.Threading.Tasks;
 using Android.App;
-using Android.Content;
 using Android.Content.PM;
 
 namespace Avalonia.Android.Platform;

src/Android/Avalonia.Android/Platform/SkiaPlatform/FramebufferManager.cs

@@ -1,4 +1,5 @@
-using Avalonia.Controls.Platform.Surfaces;
+using System;
+using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Platform;
 
 namespace Avalonia.Android.Platform.SkiaPlatform
@@ -12,8 +13,10 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             _topLevel = topLevel;
         }
 
-        public ILockedFramebuffer Lock() => new AndroidFramebuffer(_topLevel.InternalView.Holder.Surface, _topLevel.RenderScaling);
+        public ILockedFramebuffer Lock() => new AndroidFramebuffer(
-        
+            _topLevel.InternalView.Holder?.Surface ?? throw new InvalidOperationException("TopLevel.InternalView.Holder.Surface was not expected to be null."),
+            _topLevel.RenderScaling);
+
         public IFramebufferRenderTarget CreateFramebufferRenderTarget() => new FuncFramebufferRenderTarget(Lock);
     }
 }

src/Android/Avalonia.Android/Platform/SkiaPlatform/InvalidationAwareSurfaceView.cs

@@ -16,14 +16,19 @@ namespace Avalonia.Android
         readonly object _lock = new object();
         private readonly Handler _handler;
 
-        IntPtr IPlatformHandle.Handle =>
+        IntPtr IPlatformHandle.Handle => Holder?.Surface?.Handle is { } handle ?
-            AndroidFramebuffer.ANativeWindow_fromSurface(JNIEnv.Handle, Holder.Surface.Handle);
+            AndroidFramebuffer.ANativeWindow_fromSurface(JNIEnv.Handle, handle) :
+            default;
 
         public InvalidationAwareSurfaceView(Context context) : base(context)
         {
+            if (Holder is null)
+                throw new InvalidOperationException(
+                    "SurfaceView.Holder was not expected to be null during InvalidationAwareSurfaceView initialization.");
+
             Holder.AddCallback(this);
             Holder.SetFormat(global::Android.Graphics.Format.Transparent);
-            _handler = new Handler(context.MainLooper);
+            _handler = new Handler(context.MainLooper!);
         }
 
         public override void Invalidate()
@@ -34,7 +39,7 @@ namespace Avalonia.Android
                     return;
                 _handler.Post(() =>
                 {
-                    if (Holder.Surface?.IsValid != true)
+                    if (Holder?.Surface?.IsValid != true)
                         return;
                     try
                     {
@@ -77,8 +82,8 @@ namespace Avalonia.Android
         protected abstract void Draw();
         public string HandleDescriptor => "SurfaceView";
 
-        public PixelSize Size => new PixelSize(Holder.SurfaceFrame.Width(), Holder.SurfaceFrame.Height());
+        public PixelSize Size => new(Holder?.SurfaceFrame?.Width() ?? 1, Holder?.SurfaceFrame?.Height() ?? 1);
 
-        public double Scaling => Resources.DisplayMetrics.Density;
+        public double Scaling => Resources?.DisplayMetrics?.Density ?? 1;
     }
 }

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -40,66 +40,61 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         private readonly AndroidMotionEventsHelper _pointerHelper;
         private readonly AndroidInputMethod<ViewImpl> _textInputMethod;
         private readonly INativeControlHostImpl _nativeControlHost;
-        private readonly IStorageProvider _storageProvider;
+        private readonly IStorageProvider? _storageProvider;
         private readonly AndroidSystemNavigationManagerImpl _systemNavigationManager;
-        private readonly AndroidInsetsManager _insetsManager;
+        private readonly AndroidInsetsManager? _insetsManager;
         private readonly ClipboardImpl _clipboard;
-        private readonly AndroidLauncher _launcher;
+        private readonly AndroidLauncher? _launcher;
         private ViewImpl _view;
         private WindowTransparencyLevel _transparencyLevel;
 
         public TopLevelImpl(AvaloniaView avaloniaView, bool placeOnTop = false)
         {
+            if (avaloniaView.Context is null)
+            {
+                throw new ArgumentException("AvaloniaView.Context must not be null");
+            }
+            
             _view = new ViewImpl(avaloniaView.Context, this, placeOnTop);
             _textInputMethod = new AndroidInputMethod<ViewImpl>(_view);
             _keyboardHelper = new AndroidKeyboardEventsHelper<TopLevelImpl>(this);
             _pointerHelper = new AndroidMotionEventsHelper(this);
             _gl = new EglGlPlatformSurface(this);
             _framebuffer = new FramebufferManager(this);
-            _clipboard = new ClipboardImpl(avaloniaView.Context?.GetSystemService(Context.ClipboardService).JavaCast<ClipboardManager>());
+            _clipboard = new ClipboardImpl(avaloniaView.Context.GetSystemService(Context.ClipboardService).JavaCast<ClipboardManager>());
 
             RenderScaling = _view.Scaling;
 
-            MaxClientSize = new PixelSize(_view.Resources.DisplayMetrics.WidthPixels,
+            if (avaloniaView.Context is Activity mainActivity)
-                _view.Resources.DisplayMetrics.HeightPixels).ToSize(RenderScaling);
-
-            if (avaloniaView.Context is AvaloniaMainActivity mainActivity)
             {
                 _insetsManager = new AndroidInsetsManager(mainActivity, this);
+                _storageProvider = new AndroidStorageProvider(mainActivity);
+                _launcher = new AndroidLauncher(mainActivity);
             }
 
             _nativeControlHost = new AndroidNativeControlHostImpl(avaloniaView);
-            _storageProvider = new AndroidStorageProvider((Activity)avaloniaView.Context);
             _transparencyLevel = WindowTransparencyLevel.None;
-            _launcher = new AndroidLauncher((Activity)avaloniaView.Context);
 
             _systemNavigationManager = new AndroidSystemNavigationManagerImpl(avaloniaView.Context as IActivityNavigationService);
 
             Surfaces = new object[] { _gl, _framebuffer, Handle };
         }
 
-        public virtual Point GetAvaloniaPointFromEvent(MotionEvent e, int pointerIndex) =>
+        public IInputRoot? InputRoot { get; private set; }
-            new Point(e.GetX(pointerIndex), e.GetY(pointerIndex)) / RenderScaling;
-
-        public IInputRoot InputRoot { get; private set; }
 
         public virtual Size ClientSize => _view.Size.ToSize(RenderScaling);
 
         public Size? FrameSize => null;
+        
+        public Action? Closed { get; set; }
 
-        public IMouseDevice MouseDevice { get; } = new MouseDevice();
+        public Action<RawInputEventArgs>? Input { get; set; }
-
-        public Action Closed { get; set; }
-
-        public Action<RawInputEventArgs> Input { get; set; }
-
-        public Size MaxClientSize { get; protected set; }
 
-        public Action<Rect> Paint { get; set; }
+        public Action<Rect>? Paint { get; set; }
 
-        public Action<Size, WindowResizeReason> Resized { get; set; }
+        public Action<Size, WindowResizeReason>? Resized { get; set; }
 
-        public Action<double> ScalingChanged { get; set; }
+        public Action<double>? ScalingChanged { get; set; }
 
         public View View => _view;
 
@@ -109,8 +104,9 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         public IEnumerable<object> Surfaces { get; }
 
-        public Compositor Compositor => AndroidPlatform.Compositor;
+        public Compositor Compositor => AndroidPlatform.Compositor ??
-        
+            throw new InvalidOperationException("Android backend wasn't initialized. Make sure .UseAndroid() was executed.");
+
         public virtual void Hide()
         {
             _view.Visibility = ViewStates.Invisible;
@@ -131,7 +127,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             return PixelPoint.FromPoint(point, RenderScaling);
         }
 
-        public void SetCursor(ICursorImpl cursor)
+        public void SetCursor(ICursorImpl? cursor)
         {
             //still not implemented
         }
@@ -157,7 +153,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         {
             _systemNavigationManager.Dispose();
             _view.Dispose();
-            _view = null;
+            _view = null!;
         }
 
         protected virtual void OnResized(Size size)
@@ -205,37 +201,34 @@ namespace Avalonia.Android.Platform.SkiaPlatform
                 else
                 {
                     // Android 9 did this
-                    canvas.DrawColor(Color.Transparent, PorterDuff.Mode.Clear);
+                    canvas.DrawColor(Color.Transparent, PorterDuff.Mode.Clear!);
                 }
 
                 base.DispatchDraw(canvas);
             }
 
-            protected override bool DispatchGenericPointerEvent(MotionEvent e)
+            protected override bool DispatchGenericPointerEvent(MotionEvent? e)
             {
-                bool callBase;
+                var result = _tl._pointerHelper.DispatchMotionEvent(e, out var callBase);
-                bool? result = _tl._pointerHelper.DispatchMotionEvent(e, out callBase);
+                var baseResult = callBase && base.DispatchGenericPointerEvent(e);
-                bool baseResult = callBase ? base.DispatchGenericPointerEvent(e) : false;
 
-                return result != null ? result.Value : baseResult;
+                return result ?? baseResult;
             }
 
-            public override bool DispatchTouchEvent(MotionEvent e)
+            public override bool DispatchTouchEvent(MotionEvent? e)
             {
-                bool callBase;
+                var result = _tl._pointerHelper.DispatchMotionEvent(e, out var callBase);
-                bool? result = _tl._pointerHelper.DispatchMotionEvent(e, out callBase);
+                var baseResult = callBase && base.DispatchTouchEvent(e);
-                bool baseResult = callBase ? base.DispatchTouchEvent(e) : false;
 
-                return result != null ? result.Value : baseResult;
+                return result ?? baseResult;
             }
 
-            public override bool DispatchKeyEvent(KeyEvent e)
+            public override bool DispatchKeyEvent(KeyEvent? e)
             {
-                bool callBase;
+                var res = _tl._keyboardHelper.DispatchKeyEvent(e, out var callBase);
-                bool? res = _tl._keyboardHelper.DispatchKeyEvent(e, out callBase);
+                var baseResult = callBase && base.DispatchKeyEvent(e);
-                bool baseResult = callBase ? base.DispatchKeyEvent(e) : false;
 
-                return res != null ? res.Value : baseResult;
+                return res ?? baseResult;
             }
 
             void ISurfaceHolderCallback.SurfaceChanged(ISurfaceHolder holder, Format format, int width, int height)
@@ -256,29 +249,24 @@ namespace Avalonia.Android.Platform.SkiaPlatform
                 return true;
             }
 
-            private Func<TopLevelImpl, EditorInfo, IInputConnection> _initEditorInfo;
+            private Func<TopLevelImpl, EditorInfo, IInputConnection>? _initEditorInfo;
 
             public void InitEditorInfo(Func<TopLevelImpl, EditorInfo, IInputConnection> init)
             {
                 _initEditorInfo = init;
             }
 
-            public sealed override IInputConnection OnCreateInputConnection(EditorInfo outAttrs)
+            public sealed override IInputConnection OnCreateInputConnection(EditorInfo? outAttrs)
             {
-                if (_initEditorInfo != null)
+                return _initEditorInfo?.Invoke(_tl, outAttrs!)!;
-                {
-                    return _initEditorInfo(_tl, outAttrs);
-                }
-                   
-                return null;
             }
 
         }
 
-        public IPopupImpl CreatePopup() => null;
+        public IPopupImpl? CreatePopup() => null;
         
-        public Action LostFocus { get; set; }
+        public Action? LostFocus { get; set; }
-        public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
+        public Action<WindowTransparencyLevel>? TransparencyLevelChanged { get; set; }
 
         public WindowTransparencyLevel TransparencyLevel 
         {
@@ -374,7 +362,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             activity.Window?.SetBackgroundDrawable(new ColorDrawable(Color.White));
         }
 
-        public virtual object TryGetFeature(Type featureType)
+        public virtual object? TryGetFeature(Type featureType)
         {
             if (featureType == typeof(IStorageProvider))
             {
@@ -443,7 +431,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         {
             if(Input != null)
             {
-                var args = new RawTextInputEventArgs(AndroidKeyboardDevice.Instance, (ulong)DateTime.Now.Ticks, InputRoot, text);
+                var args = new RawTextInputEventArgs(AndroidKeyboardDevice.Instance!, (ulong)DateTime.Now.Ticks, InputRoot!, text);
 
                 Input(args);
             }
@@ -464,7 +452,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         public bool IgnoreChange { get; set; }
 
-        public override IEditable Replace(int start, int end, ICharSequence tb)
+        public override IEditable? Replace(int start, int end, ICharSequence? tb)
         {
             if (!IgnoreChange && start != end)
             {
@@ -474,7 +462,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             return base.Replace(start, end, tb);
         }
 
-        public override IEditable Replace(int start, int end, ICharSequence tb, int tbstart, int tbend)
+        public override IEditable? Replace(int start, int end, ICharSequence? tb, int tbstart, int tbend)
         {
             if (!IgnoreChange && start != end)
             {
@@ -486,7 +474,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         private void SelectSurroundingTextForDeletion(int start, int end)
         {
-            _inputConnection.InputMethod.Client.Selection = new TextSelection(start, end);
+            _inputConnection.InputMethod.Client!.Selection = new TextSelection(start, end);
         }
     }
 
@@ -522,8 +510,13 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             return base.SetComposingRegion(start, end);
         }
 
-        public override bool SetComposingText(ICharSequence text, int newCursorPosition)
+        public override bool SetComposingText(ICharSequence? text, int newCursorPosition)
         {
+            if (InputMethod.Client is null || text is null)
+            {
+                return false;
+            }
+
             BeginBatchEdit();
             _editable.IgnoreChange = true;
 
@@ -570,8 +563,13 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             return base.EndBatchEdit();
         }
 
-        public override bool CommitText(ICharSequence text, int newCursorPosition)
+        public override bool CommitText(ICharSequence? text, int newCursorPosition)
         {
+            if (InputMethod.Client is null || text is null)
+            {
+                return false;
+            }
+
             BeginBatchEdit();
             _commitInProgress = true;
 
@@ -639,7 +637,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             return base.PerformEditorAction(actionCode);
         }
 
-        public override ExtractedText GetExtractedText(ExtractedTextRequest request, [GeneratedEnum] GetTextFlags flags)
+        public override ExtractedText? GetExtractedText(ExtractedTextRequest? request, [GeneratedEnum] GetTextFlags flags)
         {
             if (request == null)
                 return null;

src/Android/Avalonia.Android/Platform/Specific/Helpers/AndroidKeyInterop.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System.Collections.Generic;
-
-using System.Collections.Generic;
 using Avalonia.Input;
 
 namespace Avalonia.Android.Platform.Specific.Helpers;

src/Android/Avalonia.Android/Platform/Specific/Helpers/AndroidKeyboardEventsHelper.cs

@@ -1,5 +1,3 @@
-#nullable enable
-
 using System;
 using System.Runtime.Versioning;
 using Android.Views;
@@ -22,9 +20,9 @@ namespace Avalonia.Android.Platform.Specific.Helpers
             HandleEvents = true;
         }
 
-        public bool? DispatchKeyEvent(KeyEvent e, out bool callBase)
+        public bool? DispatchKeyEvent(KeyEvent? e, out bool callBase)
         {
-            if (!HandleEvents)
+            if (!HandleEvents || e is null)
             {
                 callBase = true;
                 return null;
@@ -46,8 +44,10 @@ namespace Avalonia.Android.Platform.Specific.Helpers
         private bool? DispatchKeyEventInternal(KeyEvent e, out bool callBase)
         {
             var unicodeTextInput = OperatingSystem.IsAndroidVersionAtLeast(29) ? null : UnicodeTextInput(e);
+            var inputRoot = _view.InputRoot;
 
-            if (e.Action == KeyEventActions.Multiple && unicodeTextInput == null)
+            if ((e.Action == KeyEventActions.Multiple && unicodeTextInput == null)
+                || inputRoot is null)
             {
                 callBase = true;
                 return null;
@@ -60,7 +60,7 @@ namespace Avalonia.Android.Platform.Specific.Helpers
             var rawKeyEvent = new RawKeyEventArgs(
                           AndroidKeyboardDevice.Instance!,
                           Convert.ToUInt64(e.EventTime),
-                          _view.InputRoot,
+                          inputRoot,
                           e.Action == KeyEventActions.Down ? RawKeyEventType.KeyDown : RawKeyEventType.KeyUp,
                           AndroidKeyboardDevice.ConvertKey(e.KeyCode),
                           GetModifierKeys(e),
@@ -76,7 +76,7 @@ namespace Avalonia.Android.Platform.Specific.Helpers
                 var rawTextEvent = new RawTextInputEventArgs(
                   AndroidKeyboardDevice.Instance!,
                   Convert.ToUInt64(e.EventTime),
-                  _view.InputRoot,
+                  inputRoot,
                   unicodeTextInput ?? Convert.ToChar(e.UnicodeChar).ToString()
                   );
                 _view.Input?.Invoke(rawTextEvent);

src/Android/Avalonia.Android/Platform/Specific/Helpers/AndroidMotionEventsHelper.cs

@@ -8,8 +8,6 @@ using Avalonia.Collections.Pooled;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 
-#nullable enable
-
 namespace Avalonia.Android.Platform.Specific.Helpers
 {
     internal class AndroidMotionEventsHelper : IDisposable
@@ -30,16 +28,19 @@ namespace Avalonia.Android.Platform.Specific.Helpers
             _view = view;
         }
 
-        public bool? DispatchMotionEvent(MotionEvent e, out bool callBase)
+        public bool? DispatchMotionEvent(MotionEvent? e, out bool callBase)
         {
             callBase = true;
-            if (_disposed)
+            if (_disposed || e is null)
             {
                 return null;
             }
 
             var eventTime = (ulong)e.EventTime;
             var inputRoot = _view.InputRoot;
+            if (inputRoot is null)
+                return false; // too early to handle events.
+
             var actionMasked = e.ActionMasked;
             var modifiers = GetModifiers(e.MetaState, e.ButtonState);
 
@@ -75,7 +76,7 @@ namespace Avalonia.Android.Platform.Specific.Helpers
                             return s_intermediatePointsPooledList;
                         })
                     };
-                    _view.Input(args);
+                    _view.Input?.Invoke(args);
                 }
             }
             else
@@ -90,7 +91,7 @@ namespace Avalonia.Android.Platform.Specific.Helpers
                 {
                     var delta = new Vector(e.GetAxisValue(Axis.Hscroll), e.GetAxisValue(Axis.Vscroll));
                     var args = new RawMouseWheelEventArgs(device, eventTime, inputRoot, point.Position, delta, RawInputModifiers.None);
-                    _view.Input(args);
+                    _view.Input?.Invoke(args);
                 }
                 else
                 {
@@ -98,7 +99,7 @@ namespace Avalonia.Android.Platform.Specific.Helpers
                     if (eventType >= 0)
                     {
                         var args = new RawTouchEventArgs(device, eventTime, inputRoot, eventType, point, modifiers, e.GetPointerId(index));
-                        _view.Input(args);
+                        _view.Input?.Invoke(args);
                     }
                 }
             }

src/Android/Avalonia.Android/Platform/Storage/AndroidStorageItem.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -8,7 +6,6 @@ using System.Threading.Tasks;
 using Android;
 using Android.App;
 using Android.Content;
-using Android.OS;
 using Android.Provider;
 using Android.Webkit;
 using AndroidX.DocumentFile.Provider;
@@ -136,7 +133,7 @@ internal abstract class AndroidStorageItem : IStorageBookmarkItem
             return true;
         }
 
-        return await _activity.CheckPermission(Manifest.Permission.ReadExternalStorage);
+        return await _activity!.CheckPermission(Manifest.Permission.ReadExternalStorage);
     }
     
     public void Dispose()

src/Android/Avalonia.Android/Platform/Storage/AndroidStorageProvider.cs

@@ -1,6 +1,4 @@
-#nullable enable
+using System;
-
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
@@ -9,7 +7,6 @@ using Android.App;
 using Android.Content;
 using Android.Provider;
 using Avalonia.Platform.Storage;
-using Java.Lang;
 using AndroidUri = Android.Net.Uri;
 using Exception = System.Exception;
 using JavaFile = Java.IO.File;
@@ -244,7 +241,7 @@ internal class AndroidStorageProvider : IStorageProvider
 
         return resultList;
 
-        void OnActivityResult(int requestCode, Result resultCode, Intent data)
+        void OnActivityResult(int requestCode, Result resultCode, Intent? data)
         {
             if (currentRequestCode != requestCode)
             {

src/Android/Avalonia.Android/SingleViewLifetime.cs

@@ -1,5 +1,4 @@
-#nullable enable
+using System.Diagnostics.CodeAnalysis;
-using System.Diagnostics.CodeAnalysis;
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 

src/Android/Avalonia.Android/Stubs.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Android
 
         public IWindowImpl CreateEmbeddableWindow() => throw new NotSupportedException();
 
-        public ITrayIconImpl CreateTrayIcon() => null;
+        public ITrayIconImpl? CreateTrayIcon() => null;
     }
 
     internal class PlatformIconLoaderStub : IPlatformIconLoader

src/Headless/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -108,7 +108,6 @@ namespace Avalonia.Headless
         public Action? Deactivated { get; set; }
         public Action? Activated { get; set; }
         public IPlatformHandle Handle { get; } = new PlatformHandle(IntPtr.Zero, "STUB");
-        public Size MaxClientSize { get; } = new Size(1920, 1280);
         public void Resize(Size clientSize, WindowResizeReason reason)
         {
             if (ClientSize == clientSize)

tests/Avalonia.UnitTests/TestRoot.cs

@@ -50,8 +50,6 @@ namespace Avalonia.UnitTests
 
         public Size ClientSize { get; set; } = new Size(1000, 1000);
 
-        public Size MaxClientSize { get; set; } = Size.Infinity;
-
         public double LayoutScaling { get; set; } = 1;
 
         internal ILayoutManager LayoutManager { get; set; }