In `Avalonia.Base`, private fields that are never modified were made `readonly` (#13020)

Co-authored-by: Lehonti Ramos <lehonti@ramos>

src/Avalonia.Base/Animation/AnimationInstance`1.cs

@@ -20,17 +20,17 @@ namespace Avalonia.Animation
         private bool _playbackReversed;
         private FillMode _fillMode;
         private PlaybackDirection _playbackDirection;
-        private Animator<T> _animator;
-        private Animation _animation;
-        private Animatable _targetControl;
+        private readonly Animator<T> _animator;
+        private readonly Animation _animation;
+        private readonly Animatable _targetControl;
         private T _neutralValue;
         private double _speedRatioConv;
         private TimeSpan _initialDelay;
         private TimeSpan _iterationDelay;
         private TimeSpan _duration;
         private Easings.Easing? _easeFunc;
-        private Action? _onCompleteAction;
-        private Func<double, T, T> _interpolator;
+        private readonly Action? _onCompleteAction;
+        private readonly Func<double, T, T> _interpolator;
         private IDisposable? _timerSub;
         private readonly IClock _baseClock;
         private IClock? _clock;

src/Avalonia.Base/Animation/Animators/BoxShadowAnimator.cs

@@ -4,9 +4,9 @@ namespace Avalonia.Animation.Animators
 {
     internal class BoxShadowAnimator : Animator<BoxShadow>
     {
-        static ColorAnimator s_colorAnimator = new ColorAnimator();
-        static DoubleAnimator s_doubleAnimator = new DoubleAnimator();
-        static BoolAnimator s_boolAnimator = new BoolAnimator();
+        static readonly ColorAnimator s_colorAnimator = new ColorAnimator();
+        static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();
+        static readonly BoolAnimator s_boolAnimator = new BoolAnimator();
         public override BoxShadow Interpolate(double progress, BoxShadow oldValue, BoxShadow newValue)
         {
             return new BoxShadow

src/Avalonia.Base/Animation/DisposeAnimationInstanceSubject.cs

@@ -10,11 +10,11 @@ namespace Avalonia.Animation
     {
         private IDisposable? _lastInstance;
         private bool _lastMatch;
-        private Animator<T> _animator;
-        private Animation _animation;
-        private Animatable _control;
-        private Action? _onComplete;
-        private IClock? _clock;
+        private readonly Animator<T> _animator;
+        private readonly Animation _animation;
+        private readonly Animatable _control;
+        private readonly Action? _onComplete;
+        private readonly IClock? _clock;
 
         public DisposeAnimationInstanceSubject(Animator<T> animator, Animation animation, Animatable control, IClock? clock, Action? onComplete)
         {

src/Avalonia.Base/AvaloniaObjectExtensions.cs

@@ -369,7 +369,7 @@ namespace Avalonia
 
         private class BindingAdaptor : IBinding
         {
-            private IObservable<object?> _source;
+            private readonly IObservable<object?> _source;
 
             public BindingAdaptor(IObservable<object?> source)
             {

src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs

@@ -60,7 +60,7 @@ namespace Avalonia.Collections
         private class WeakCollectionChangedObservable : LightweightObservableBase<NotifyCollectionChangedEventArgs>,
             IWeakEventSubscriber<NotifyCollectionChangedEventArgs>
         {
-            private WeakReference<INotifyCollectionChanged> _sourceReference;
+            private readonly WeakReference<INotifyCollectionChanged> _sourceReference;
 
             public WeakCollectionChangedObservable(WeakReference<INotifyCollectionChanged> source)
             {

src/Avalonia.Base/Data/BindingChainException.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Data
     /// </summary>
     public class BindingChainException : Exception
     {
-        private string _message;
+        private readonly string _message;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="BindingChainException"/> class.

src/Avalonia.Base/Data/Core/ExpressionObserver.cs

@@ -48,8 +48,8 @@ namespace Avalonia.Data.Core
                 new ObservableStreamPlugin(),
             };
         private readonly ExpressionNode _node;
-        private object? _root;
-        private Func<object?>? _rootGetter;
+        private readonly object? _root;
+        private readonly Func<object?>? _rootGetter;
         private IDisposable? _rootSubscription;
         private WeakReference<object?>? _value;
         private IReadOnlyList<ITransformNode>? _transformNodes;

src/Avalonia.Base/Data/Core/Parsers/ExpressionVisitorNodeBuilder.cs

@@ -11,8 +11,8 @@ namespace Avalonia.Data.Core.Parsers
     class ExpressionVisitorNodeBuilder : ExpressionVisitor
     {
         private const string MultiDimensionalArrayGetterMethodName = "Get";
-        private static PropertyInfo AvaloniaObjectIndexer;
-        private static MethodInfo CreateDelegateMethod;
+        private static readonly PropertyInfo AvaloniaObjectIndexer;
+        private static readonly MethodInfo CreateDelegateMethod;
 
         private readonly bool _enableDataValidation;
 

src/Avalonia.Base/Data/Core/Plugins/PropertyError.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Data.Core.Plugins
     /// </summary>
     public class PropertyError : IPropertyAccessor
     {
-        private BindingNotification _error;
+        private readonly BindingNotification _error;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PropertyError"/> class.

src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Data.Core
     internal class PropertyAccessorNode : SettableNode
     {
         private readonly bool _enableValidation;
-        private IPropertyAccessorPlugin? _customPlugin;
+        private readonly IPropertyAccessorPlugin? _customPlugin;
         private IPropertyAccessor? _accessor;
 
         public PropertyAccessorNode(string propertyName, bool enableValidation)

src/Avalonia.Base/Data/Core/StreamNode.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Data.Core
     [RequiresUnreferencedCode(TrimmingMessages.ExpressionNodeRequiresUnreferencedCodeMessage)]
     internal class StreamNode : ExpressionNode
     {
-        private IStreamPlugin? _customPlugin = null;
+        private readonly IStreamPlugin? _customPlugin = null;
         private IDisposable? _subscription;
 
         public override string Description => "^";

src/Avalonia.Base/Input/Cursor.cs

@@ -42,7 +42,7 @@ namespace Avalonia.Input
     public class Cursor : IDisposable
     {
         public static readonly Cursor Default = new Cursor(StandardCursorType.Arrow);
-        private string _name;
+        private readonly string _name;
 
         private Cursor(ICursorImpl platformImpl, string name)
         {

src/Avalonia.Base/Layout/LayoutManager.cs

@@ -29,7 +29,7 @@ namespace Avalonia.Layout
         private bool _queued;
         private bool _running;
         private int _totalPassCount;
-        private Action _invokeOnRender;
+        private readonly Action _invokeOnRender;
 
         public LayoutManager(ILayoutRoot owner)
         {

src/Avalonia.Base/Media/BoxShadow.cs

@@ -44,7 +44,7 @@ namespace Avalonia.Media
         struct ArrayReader
         {
             private int _index;
-            private string[] _arr;
+            private readonly string[] _arr;
 
             public ArrayReader(string[] arr)
             {

src/Avalonia.Base/Media/BoxShadows.cs

@@ -61,7 +61,7 @@ namespace Avalonia.Media
 #pragma warning restore CA1815 // Override equals and operator equals on value types
         {
             private int _index;
-            private BoxShadows _shadows;
+            private readonly BoxShadows _shadows;
 
             public BoxShadowsEnumerator(BoxShadows shadows)
             {

src/Avalonia.Base/Media/FormattedText.cs

@@ -23,11 +23,11 @@ namespace Avalonia.Media
         private const double MaxFontEmSize = RealInfiniteWidth / GreatestMultiplierOfEm;
 
         // properties and format runs
-        private string _text;
+        private readonly string _text;
         private readonly SpanVector _formatRuns = new SpanVector(null);
         private SpanPosition _latestPosition;
 
-        private GenericTextParagraphProperties _defaultParaProps;
+        private readonly GenericTextParagraphProperties _defaultParaProps;
 
         private double _maxTextWidth = double.PositiveInfinity;
         private double[]? _maxTextWidths;

src/Avalonia.Base/Media/Geometry.cs

@@ -21,7 +21,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<Geometry, Transform?>(nameof(Transform));
 
         private bool _isDirty = true;
-        private bool _canInvaldate = true;
+        private readonly bool _canInvaldate = true;
         private IGeometryImpl? _platformImpl;
 
         static Geometry()

src/Avalonia.Base/Media/Imaging/Bitmap.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Media.Imaging
     /// </summary>
     public class Bitmap : IBitmap, IImageBrushSource
     {
-        private bool _isTranscoded;
+        private readonly bool _isTranscoded;
         /// <summary>
         /// Loads a Bitmap from a stream and decodes at the desired width. Aspect ratio is maintained.
         /// This is more efficient than loading and then resizing.

src/Avalonia.Base/Media/Imaging/PixelFormatReaders.cs

@@ -94,7 +94,7 @@ internal static unsafe class PixelFormatReader
             _bit = 0;
         }
 
-        private static Rgba8888Pixel[] Palette = new[]
+        private static readonly Rgba8888Pixel[] Palette = new[]
         {
             s_black,
             new Rgba8888Pixel

src/Avalonia.Base/Media/Imaging/WriteableBitmap.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Media.Imaging
     public class WriteableBitmap : Bitmap
     {
         // Holds a buffer with pixel format that requires transcoding
-        private BitmapMemory? _pixelFormatMemory = null;
+        private readonly BitmapMemory? _pixelFormatMemory = null;
         
         /// <summary>
         /// Initializes a new instance of the <see cref="WriteableBitmap"/> class.

src/Avalonia.Base/Media/MediaContext.Clock.cs

@@ -15,8 +15,8 @@ internal partial class MediaContext
     class MediaContextClock : IGlobalClock
     {
         private readonly MediaContext _parent;
-        private List<IObserver<TimeSpan>> _observers = new();
-        private List<IObserver<TimeSpan>> _newObservers = new();
+        private readonly List<IObserver<TimeSpan>> _observers = new();
+        private readonly List<IObserver<TimeSpan>> _newObservers = new();
         private Queue<Action<TimeSpan>> _queuedAnimationFrames = new();
         private Queue<Action<TimeSpan>> _queuedAnimationFramesNext = new();
         private TimeSpan _currentAnimationTimestamp;

src/Avalonia.Base/Media/MediaContext.cs

@@ -26,7 +26,7 @@ internal partial class MediaContext : ICompositorScheduler
     private List<Action>? _invokeOnRenderCallbacks;
     private readonly Stack<List<Action>> _invokeOnRenderCallbackListPool = new();
 
-    private DispatcherTimer _animationsTimer = new(DispatcherPriority.Render)
+    private readonly DispatcherTimer _animationsTimer = new(DispatcherPriority.Render)
     {
         // Since this timer is used to drive animations that didn't contribute to the previous frame at all
         // We can safely use 16ms interval until we fix our animation system to actually report the next expected 
@@ -34,7 +34,7 @@ internal partial class MediaContext : ICompositorScheduler
         Interval = TimeSpan.FromMilliseconds(16)
     };
 
-    private Dictionary<object, TopLevelInfo> _topLevels = new();
+    private readonly Dictionary<object, TopLevelInfo> _topLevels = new();
 
     private MediaContext(Dispatcher dispatcher)
     {

src/Avalonia.Base/Media/UnicodeRange.cs

@@ -104,7 +104,7 @@ namespace Avalonia.Media
 
     public readonly record struct UnicodeRangeSegment
     {
-        private static Regex s_regex = new Regex(@"^(?:[uU]\+)?(?:([0-9a-fA-F](?:[0-9a-fA-F?]{1,5})?))$", RegexOptions.Compiled);
+        private static readonly Regex s_regex = new Regex(@"^(?:[uU]\+)?(?:([0-9a-fA-F](?:[0-9a-fA-F?]{1,5})?))$", RegexOptions.Compiled);
 
         public UnicodeRangeSegment(int start, int end)
         {

src/Avalonia.Base/PropertyStore/EffectiveValue`1.cs

@@ -17,7 +17,7 @@ namespace Avalonia.PropertyStore
     {
         private readonly StyledPropertyMetadata<T> _metadata;
         private T? _baseValue;
-        private UncommonFields? _uncommon;
+        private readonly UncommonFields? _uncommon;
 
         public EffectiveValue(
             AvaloniaObject owner,

src/Avalonia.Base/Reactive/Operators/Sink.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Reactive.Operators;
 internal abstract class Sink<TTarget> : IDisposable
 {
     private IDisposable? _upstream;
-    private volatile IObserver<TTarget> _observer;
+    private readonly IObserver<TTarget> _observer;
 
     protected Sink(IObserver<TTarget> observer)
     {

src/Avalonia.Base/Rendering/Composition/Animations/ImplicitAnimationCollection.cs

@@ -19,8 +19,8 @@ namespace Avalonia.Rendering.Composition.Animations
     /// </remarks>
     public class ImplicitAnimationCollection : CompositionObject, IDictionary<string, ICompositionAnimationBase>
     {
-        private Dictionary<string, ICompositionAnimationBase> _inner = new Dictionary<string, ICompositionAnimationBase>();
-        private IDictionary<string, ICompositionAnimationBase> _innerface;
+        private readonly Dictionary<string, ICompositionAnimationBase> _inner = new Dictionary<string, ICompositionAnimationBase>();
+        private readonly IDictionary<string, ICompositionAnimationBase> _innerface;
         internal ImplicitAnimationCollection(Compositor compositor) : base(compositor, null)
         {
             _innerface = _inner;

src/Avalonia.Base/Rendering/Composition/Compositor.cs

@@ -20,20 +20,20 @@ namespace Avalonia.Rendering.Composition
     {
         internal IRenderLoop Loop { get; }
         internal bool UseUiThreadForSynchronousCommits { get; }
-        private ServerCompositor _server;
+        private readonly ServerCompositor _server;
         private CompositionBatch? _nextCommit;
-        private BatchStreamObjectPool<object?> _batchObjectPool;
-        private BatchStreamMemoryPool _batchMemoryPool;
-        private Queue<ICompositorSerializable> _objectSerializationQueue = new();
-        private HashSet<ICompositorSerializable> _objectSerializationHashSet = new();
+        private readonly BatchStreamObjectPool<object?> _batchObjectPool;
+        private readonly BatchStreamMemoryPool _batchMemoryPool;
+        private readonly Queue<ICompositorSerializable> _objectSerializationQueue = new();
+        private readonly HashSet<ICompositorSerializable> _objectSerializationHashSet = new();
         private Queue<Action> _invokeBeforeCommitWrite = new(), _invokeBeforeCommitRead = new();
-        private HashSet<IDisposable> _disposeOnNextBatch = new();
+        private readonly HashSet<IDisposable> _disposeOnNextBatch = new();
         internal ServerCompositor Server => _server;
         private CompositionBatch? _pendingBatch;
         private readonly object _pendingBatchLock = new();
-        private List<Action> _pendingServerCompositorJobs = new();
+        private readonly List<Action> _pendingServerCompositorJobs = new();
         private DiagnosticTextRenderer? _diagnosticTextRenderer;
-        private Action _triggerCommitRequested;
+        private readonly Action _triggerCommitRequested;
 
         internal IEasing DefaultEasing { get; }
 

src/Avalonia.Base/Rendering/Composition/Drawing/CompositionRenderDataSceneBrushContent.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Rendering.Composition.Drawing;
 internal class CompositionRenderDataSceneBrushContent : ISceneBrushContent
 {
     public CompositionRenderData RenderData { get; }
-    private Rect? _rect;
+    private readonly Rect? _rect;
 
     public CompositionRenderDataSceneBrushContent(ITileBrush brush, CompositionRenderData renderData, Rect? rect,
         bool useScalableRasterization)

src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionTrackedValues.cs

@@ -6,8 +6,8 @@ namespace Avalonia.Rendering.Composition.Expressions;
 
 internal class ExpressionTrackedObjects : IEnumerable<IExpressionObject>
 {
-    private List<IExpressionObject> _list = new();
-    private HashSet<IExpressionObject> _hashSet = new();
+    private readonly List<IExpressionObject> _list = new();
+    private readonly HashSet<IExpressionObject> _hashSet = new();
     
     public void Add(IExpressionObject obj, string member)
     {
@@ -35,7 +35,7 @@ internal class ExpressionTrackedObjects : IEnumerable<IExpressionObject>
     
     public struct Pool
     {
-        private Stack<ExpressionTrackedObjects> _stack = new();
+        private readonly Stack<ExpressionTrackedObjects> _stack = new();
 
         public Pool()
         {

src/Avalonia.Base/Rendering/Composition/Server/DrawingContextProxy.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Rendering.Composition.Server;
 internal class CompositorDrawingContextProxy : IDrawingContextImpl,
     IDrawingContextWithAcrylicLikeSupport, IDrawingContextImplWithEffects
 {
-    private IDrawingContextImpl _impl;
+    private readonly IDrawingContextImpl _impl;
 
     public CompositorDrawingContextProxy(IDrawingContextImpl impl)
     {

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionTarget.cs

@@ -26,13 +26,13 @@ namespace Avalonia.Rendering.Composition.Server
         private FrameTimeGraph? _renderTimeGraph;
         private FrameTimeGraph? _layoutTimeGraph;
         private Rect _dirtyRect;
-        private Random _random = new();
+        private readonly Random _random = new();
         private Size _layerSize;
         private IDrawingContextLayerImpl? _layer;
         private bool _redrawRequested;
         private bool _disposed;
-        private HashSet<ServerCompositionVisual> _attachedVisuals = new();
-        private Queue<ServerCompositionVisual> _adornerUpdateQueue = new();
+        private readonly HashSet<ServerCompositionVisual> _attachedVisuals = new();
+        private readonly Queue<ServerCompositionVisual> _adornerUpdateQueue = new();
 
         public long Id { get; }
         public ulong Revision { get; private set; }

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.RenderResources.cs

@@ -4,8 +4,8 @@ namespace Avalonia.Rendering.Composition.Server;
 
 partial class ServerCompositor
 {
-    private Queue<IServerRenderResource> _renderResourcesInvalidationQueue = new();
-    private HashSet<IServerRenderResource> _renderResourcesInvalidationSet = new();
+    private readonly Queue<IServerRenderResource> _renderResourcesInvalidationQueue = new();
+    private readonly HashSet<IServerRenderResource> _renderResourcesInvalidationSet = new();
     
     public void ApplyEnqueuedRenderResourceChanges()
     {

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.cs

@@ -26,12 +26,12 @@ namespace Avalonia.Rendering.Composition.Server
         public long LastBatchId { get; private set; }
         public Stopwatch Clock { get; } = Stopwatch.StartNew();
         public TimeSpan ServerNow { get; private set; }
-        private List<ServerCompositionTarget> _activeTargets = new();
-        private HashSet<IServerClockItem> _clockItems = new();
-        private List<IServerClockItem> _clockItemsToUpdate = new();
+        private readonly List<ServerCompositionTarget> _activeTargets = new();
+        private readonly HashSet<IServerClockItem> _clockItems = new();
+        private readonly List<IServerClockItem> _clockItemsToUpdate = new();
         internal BatchStreamObjectPool<object?> BatchObjectPool;
         internal BatchStreamMemoryPool BatchMemoryPool;
-        private object _lock = new object();
+        private readonly object _lock = new object();
         private Thread? _safeThread;
         private bool _uiThreadIsInsideRender;
         public PlatformRenderInterfaceContextManager RenderInterface { get; }
@@ -57,8 +57,8 @@ namespace Avalonia.Rendering.Composition.Server
 
         internal void UpdateServerTime() => ServerNow = Clock.Elapsed;
 
-        List<CompositionBatch> _reusableToNotifyProcessedList = new();
-        List<CompositionBatch> _reusableToNotifyRenderedList = new();
+        readonly List<CompositionBatch> _reusableToNotifyProcessedList = new();
+        readonly List<CompositionBatch> _reusableToNotifyRenderedList = new();
         void ApplyPendingBatches()
         {
             while (true)

src/Avalonia.Base/Rendering/Composition/Transport/Batch.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Rendering.Composition.Transport
     public class CompositionBatch
     {
         private static long _nextSequenceId = 1;
-        private static ConcurrentBag<BatchStreamData> _pool = new();
+        private static readonly ConcurrentBag<BatchStreamData> _pool = new();
         private readonly TaskCompletionSource<int> _acceptedTcs = new();
         private readonly TaskCompletionSource<int> _renderedTcs = new();
         

src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs

@@ -17,7 +17,7 @@ internal abstract class BatchStreamPoolBase<T> : IDisposable
     int _usage;
     readonly int[] _usageStatistics = new int[10];
     int _usageStatisticsSlot;
-    bool _reclaimImmediately;
+    readonly bool _reclaimImmediately;
 
     public int CurrentUsage => _usage;
     public int CurrentPool => _pool.Count;

src/Avalonia.Base/Rendering/Composition/VisualCollection.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Rendering.Composition
     /// </summary>
     public partial class CompositionVisualCollection : CompositionObject
     {
-        private CompositionVisual _owner;
+        private readonly CompositionVisual _owner;
         internal CompositionVisualCollection(CompositionVisual parent, ServerCompositionVisualCollection server) : base(parent.Compositor, server)
         {
             _owner = parent;

src/Avalonia.Base/Rendering/RenderLoop.cs

@@ -16,11 +16,11 @@ namespace Avalonia.Rendering
     /// </remarks>
     internal class RenderLoop : IRenderLoop
     {
-        private List<IRenderLoopTask> _items = new List<IRenderLoopTask>();
-        private List<IRenderLoopTask> _itemsCopy = new List<IRenderLoopTask>();
+        private readonly List<IRenderLoopTask> _items = new List<IRenderLoopTask>();
+        private readonly List<IRenderLoopTask> _itemsCopy = new List<IRenderLoopTask>();
         private IRenderTimer? _timer;
         private int _inTick;
-        private int _inUpdate;
+        private readonly int _inUpdate;
         
         public static IRenderLoop LocatorAutoInstance
         {

src/Avalonia.Base/Rendering/SwapchainBase.cs

@@ -13,7 +13,7 @@ abstract class SwapchainBase<TImage> : IAsyncDisposable where TImage : class, IS
 {
     protected ICompositionGpuInterop Interop { get; }
     protected CompositionDrawingSurface Target { get; }
-    private List<TImage> _pendingImages = new();
+    private readonly List<TImage> _pendingImages = new();
 
     public SwapchainBase(ICompositionGpuInterop interop, CompositionDrawingSurface target)
     {

src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs

@@ -13,7 +13,7 @@ public partial class Dispatcher
     private bool _hasShutdownFinished;
     private bool _startingShutdown;
     
-    private Stack<DispatcherFrame> _frames = new();
+    private readonly Stack<DispatcherFrame> _frames = new();
     
 
     /// <summary>

src/Avalonia.Base/Threading/Dispatcher.Queue.cs

@@ -11,7 +11,7 @@ public partial class Dispatcher
     private bool _explicitBackgroundProcessingRequested;
     private const int MaximumInputStarvationTimeInFallbackMode = 50;
     private const int MaximumInputStarvationTimeInExplicitProcessingExplicitMode = 50;
-    private int _maximumInputStarvationTime;
+    private readonly int _maximumInputStarvationTime;
     
     void RequestBackgroundProcessing()
     {

src/Avalonia.Base/Threading/Dispatcher.Timers.cs

@@ -6,7 +6,7 @@ namespace Avalonia.Threading;
 
 public partial class Dispatcher
 {
-    private List<DispatcherTimer> _timers = new();
+    private readonly List<DispatcherTimer> _timers = new();
     private long _timersVersion;
     private bool _dueTimeFound;
     private long _dueTimeInMs;

src/Avalonia.Base/Threading/DispatcherFrame.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Threading;
 /// </summary>
 public class DispatcherFrame
 {
-    private bool _exitWhenRequested;
+    private readonly bool _exitWhenRequested;
     private bool _continue;
     private bool _isRunning;
     private CancellationTokenSource? _cancellationTokenSource;

src/Avalonia.Base/Threading/DispatcherOperation.cs

@@ -224,8 +224,8 @@ public class DispatcherOperation
 
         private void OnCompletedOrAborted(object? sender, EventArgs e) => Exit();
 
-        private DispatcherOperation _operation;
-        private Timer? _waitTimer;
+        private readonly DispatcherOperation _operation;
+        private readonly Timer? _waitTimer;
     }
 
     public Task GetTask() => GetTaskCore();

src/Avalonia.Base/Threading/DispatcherTimer.cs

@@ -334,15 +334,15 @@ public partial class DispatcherTimer
     }
 
     // This is the object we use to synchronize access.
-    private object _instanceLock = new object();
+    private readonly object _instanceLock = new object();
 
     // Note: We cannot BE a dispatcher-affinity object because we can be
     // created by a worker thread.  We are still associated with a
     // dispatcher (where we post the item) but we can be accessed
     // by any thread.
-    private Dispatcher _dispatcher;
+    private readonly Dispatcher _dispatcher;
 
-    private DispatcherPriority _priority; // NOTE: should be Priority
+    private readonly DispatcherPriority _priority; // NOTE: should be Priority
     private TimeSpan _interval;
     private DispatcherOperation? _operation;
     private bool _isEnabled;

src/Avalonia.Base/Threading/IDispatcherImpl.cs

@@ -46,7 +46,7 @@ internal class LegacyDispatcherImpl : IDispatcherImpl
 {
     private readonly IPlatformThreadingInterface _platformThreading;
     private IDisposable? _timer;
-    private Stopwatch _clock = Stopwatch.StartNew();
+    private readonly Stopwatch _clock = Stopwatch.StartNew();
 
     public LegacyDispatcherImpl(IPlatformThreadingInterface platformThreading)
     {

src/Avalonia.Base/Threading/ThreadSafeObjectPool.cs

@@ -4,7 +4,7 @@ namespace Avalonia.Threading
 {
     internal class ThreadSafeObjectPool<T> where T : class, new()
     {
-        private Stack<T> _stack = new Stack<T>();
+        private readonly Stack<T> _stack = new Stack<T>();
         public static ThreadSafeObjectPool<T> Default { get; } = new ThreadSafeObjectPool<T>();
 
         public T Get()

src/Avalonia.Base/Utilities/PooledInlineList.cs

@@ -150,9 +150,9 @@ internal struct PooledInlineList<T> : IDisposable, IEnumerable<T> where T : clas
     
     public struct Enumerator : IEnumerator<T>
     {
-        private T? _singleItem;
+        private readonly T? _singleItem;
         private int _index;
-        private SimplePooledList? _list;
+        private readonly SimplePooledList? _list;
         
         public Enumerator(object? item)
         {

src/Avalonia.Base/Utilities/Ref.cs

@@ -105,8 +105,8 @@ namespace Avalonia.Utilities
         class Ref<T> : CriticalFinalizerObject, IRef<T> where T : class
         {
             private T? _item;
-            private RefCounter _counter;
-            private object _lock = new object();
+            private readonly RefCounter _counter;
+            private readonly object _lock = new object();
 
             public Ref(T item, RefCounter counter)
             {

src/Avalonia.Base/Utilities/SingleOrDictionary.cs

@@ -99,7 +99,7 @@ namespace Avalonia.Utilities
 
         private class SingleEnumerator<T> : IEnumerator<T>
         {
-            private T value;
+            private readonly T value;
             private int index = -1;
 
             public SingleEnumerator(T value)

src/Avalonia.Base/Utilities/SmallDictionary.cs

@@ -294,7 +294,7 @@ internal struct InlineDictionary<TKey, TValue> : IEnumerable<KeyValuePair<TKey,
         private readonly KeyValuePair[]? _arr;
         private KeyValuePair<TKey, TValue> _first;
         private int _index;
-        private Type _type;
+        private readonly Type _type;
         enum Type
         {
             Empty, Single, Array, Dictionary

src/Avalonia.Base/Utilities/SpringSolver.cs

@@ -31,11 +31,11 @@ namespace Avalonia.Utilities;
 
 internal struct SpringSolver 
 {
-    private double m_w0;
-    private double m_zeta;
-    private double m_wd;
-    private double m_A;
-    private double m_B;
+    private readonly double m_w0;
+    private readonly double m_zeta;
+    private readonly double m_wd;
+    private readonly double m_A;
+    private readonly double m_B;
 
     /// <summary>
     ///