Avoid "using system" because

src/iOS/Avalonia.iOS/AvaloniaAppDelegate.cs

@@ -12,7 +12,7 @@ namespace Avalonia.iOS
         
         [Export("window")]
         public UIWindow Window { get; set; }
-
+        
         [Export("application:didFinishLaunchingWithOptions:")]
         public bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
         {

src/iOS/Avalonia.iOS/AvaloniaView.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Controls.Embedding;
@@ -94,14 +93,14 @@ namespace Avalonia.iOS
             public Size? FrameSize => null;
             public double RenderScaling => _view.ContentScaleFactor;
             public IEnumerable<object> Surfaces { get; set; }
-            public Action<RawInputEventArgs> Input { get; set; }
-            public Action<Rect> Paint { get; set; }
-            public Action<Size, PlatformResizeReason> Resized { get; set; }
-            public Action<double> ScalingChanged { get; set; }
-            public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
-            public Action Closed { get; set; }
-
-            public Action LostFocus { get; set; }
+            public System.Action<RawInputEventArgs> Input { get; set; }
+            public System.Action<Rect> Paint { get; set; }
+            public System.Action<Size, PlatformResizeReason> Resized { get; set; }
+            public System.Action<double> ScalingChanged { get; set; }
+            public System.Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
+            public System.Action Closed { get; set; }
+
+            public System.Action LostFocus { get; set; }
 
             // legacy no-op
             public IMouseDevice MouseDevice { get; } = new MouseDevice();

src/iOS/Avalonia.iOS/ClipboardImpl.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Threading.Tasks;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
@@ -25,10 +24,10 @@ namespace Avalonia.iOS
             return Task.FromResult(0);
         }
 
-        public Task SetDataObjectAsync(IDataObject data) => throw new PlatformNotSupportedException();
+        public Task SetDataObjectAsync(IDataObject data) => throw new System.PlatformNotSupportedException();
 
-        public Task<string[]> GetFormatsAsync() => throw new PlatformNotSupportedException();
+        public Task<string[]> GetFormatsAsync() => throw new System.PlatformNotSupportedException();
 
-        public Task<object> GetDataAsync(string format) => throw new PlatformNotSupportedException();
+        public Task<object> GetDataAsync(string format) => throw new System.PlatformNotSupportedException();
     }
-}
+}

src/iOS/Avalonia.iOS/DisplayLinkTimer.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
@@ -11,7 +10,7 @@ namespace Avalonia.iOS
 {
     class DisplayLinkTimer : IRenderTimer
     {
-        public event Action<TimeSpan> Tick;
+        public event System.Action<System.TimeSpan> Tick;
         private Stopwatch _st = Stopwatch.StartNew();
 
         public DisplayLinkTimer()
@@ -34,4 +33,4 @@ namespace Avalonia.iOS
             Tick?.Invoke(_st.Elapsed);
         }
     }
-}
+}

src/iOS/Avalonia.iOS/EaglDisplay.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Reactive.Disposables;
 using Avalonia.OpenGL;
 using OpenGLES;
@@ -8,7 +7,7 @@ namespace Avalonia.iOS
     class EaglFeature : IPlatformOpenGlInterface
     {
         public IGlContext PrimaryContext => Context;
-        public IGlContext CreateSharedContext() => throw new NotSupportedException();
+        public IGlContext CreateSharedContext() => throw new System.NotSupportedException();
         public bool CanShareContexts => false;
         public bool CanCreateContexts => false;
         public IGlContext CreateContext() => throw new System.NotSupportedException();
@@ -23,7 +22,7 @@ namespace Avalonia.iOS
         {
             const string path = "/System/Library/Frameworks/OpenGLES.framework/OpenGLES";
             var libGl = ObjCRuntime.Dlfcn.dlopen(path, 1);
-            if (libGl == IntPtr.Zero)
+            if (libGl == System.IntPtr.Zero)
                 throw new OpenGlException("Unable to load " + path);
             GlInterface = new GlInterface(Version, proc => ObjCRuntime.Dlfcn.dlsym(libGl, proc));
             Context = new EAGLContext(EAGLRenderingAPI.OpenGLES3);
@@ -35,7 +34,7 @@ namespace Avalonia.iOS
             Context = null;
         }
 
-        class ResetContext : IDisposable
+        class ResetContext : System.IDisposable
         {
             private EAGLContext _old;
             private bool _disposed;
@@ -55,7 +54,7 @@ namespace Avalonia.iOS
             }
         }
         
-        public IDisposable MakeCurrent()
+        public System.IDisposable MakeCurrent()
         {
             var old = EAGLContext.CurrentContext;
             if (!EAGLContext.SetCurrentContext(Context))
@@ -63,7 +62,7 @@ namespace Avalonia.iOS
             return new ResetContext(old);
         }
 
-        public IDisposable EnsureCurrent()
+        public System.IDisposable EnsureCurrent()
         {
             if(EAGLContext.CurrentContext == Context)
                 return Disposable.Empty;

src/iOS/Avalonia.iOS/EaglLayerSurface.cs

@@ -1,5 +1,3 @@
-
-using System;
 using System.Threading;
 using Avalonia.OpenGL;
 using Avalonia.OpenGL.Surfaces;
@@ -19,10 +17,10 @@ namespace Avalonia.iOS
         class RenderSession : IGlPlatformSurfaceRenderingSession
         {
             private readonly GlContext _ctx;
-            private readonly IDisposable _restoreContext;
+            private readonly System.IDisposable _restoreContext;
             private readonly SizeSynchronizedLayerFbo _fbo;
 
-            public RenderSession(GlContext ctx, IDisposable restoreContext, SizeSynchronizedLayerFbo fbo)
+            public RenderSession(GlContext ctx, System.IDisposable restoreContext, SizeSynchronizedLayerFbo fbo)
             {
                 _ctx = ctx;
                 _restoreContext = restoreContext;
@@ -75,7 +73,7 @@ namespace Avalonia.iOS
         static void CheckThread()
         {
             if (Platform.Timer.TimerThread != Thread.CurrentThread)
-                throw new InvalidOperationException("Invalid thread, go away");
+                throw new System.InvalidOperationException("Invalid thread, go away");
         }
         
         public IGlPlatformSurfaceRenderTarget CreateGlRenderTarget()
@@ -86,7 +84,7 @@ namespace Avalonia.iOS
             {
                 var fbo = new SizeSynchronizedLayerFbo(ctx.Context, ctx.GlInterface, _layer);
                 if (!fbo.Sync())
-                    throw new InvalidOperationException("Unable to create render target");
+                    throw new System.InvalidOperationException("Unable to create render target");
                 return new RenderTarget(ctx, fbo);
             }
         }

src/iOS/Avalonia.iOS/Extensions.cs

@@ -1,4 +1,3 @@
-using System;
 using Avalonia.Media;
 using CoreGraphics;
 using UIKit;

src/iOS/Avalonia.iOS/LayerFbo.cs

@@ -1,8 +1,12 @@
-using System;
 using Avalonia.OpenGL;
 using CoreAnimation;
 using OpenGLES;
 
+// We can't import System because System has a type called nint on iOS and Mac Catalyst.
+// As such, throughout this file System is fully qualified.
+// See https://github.com/xamarin/xamarin-macios/issues/10508
+// And https://github.com/dotnet/Silk.NET/blob/main/src/Windowing/Silk.NET.Windowing.Sdl/SdlView.cs
+
 namespace Avalonia.iOS
 {
     public class LayerFbo
@@ -92,11 +96,11 @@ namespace Avalonia.iOS
             _gl.DeleteRenderbuffers(1, _depthBuffer);
             _gl.DeleteRenderbuffers(1, _renderbuffer);
             if (_context != EAGLContext.CurrentContext)
-                throw new InvalidOperationException("Associated EAGLContext is not current");
+                throw new System.InvalidOperationException("Associated EAGLContext is not current");
         }
     }
 
-    class SizeSynchronizedLayerFbo : IDisposable
+    class SizeSynchronizedLayerFbo : System.IDisposable
     {
         private readonly EAGLContext _context;
         private readonly GlInterface _gl;
@@ -130,7 +134,7 @@ namespace Avalonia.iOS
         public void Dispose()
         {
             if (_context != EAGLContext.CurrentContext)
-                throw new InvalidOperationException("Associated EAGLContext is not current");
+                throw new System.InvalidOperationException("Associated EAGLContext is not current");
             _fbo?.Dispose();
             _fbo = null;
         }
@@ -138,7 +142,7 @@ namespace Avalonia.iOS
         public void Bind()
         {
             if(!Sync())
-                throw new InvalidOperationException("Unable to create a render target");
+                throw new System.InvalidOperationException("Unable to create a render target");
             _fbo.Bind();
         }
 

src/iOS/Avalonia.iOS/Platform.cs

@@ -1,5 +1,3 @@
-using System;
-
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
@@ -32,11 +30,11 @@ namespace Avalonia.iOS
             public Size TouchDoubleClickSize => new Size(10, 10);
 
             /// <inheritdoc cref="IPlatformSettings.TouchDoubleClickTime"/>
-            public TimeSpan TouchDoubleClickTime => TimeSpan.FromMilliseconds(500);
+            public System.TimeSpan TouchDoubleClickTime => System.TimeSpan.FromMilliseconds(500);
 
             public Size DoubleClickSize => new Size(4, 4);
 
-            public TimeSpan DoubleClickTime => TouchDoubleClickTime;
+            public System.TimeSpan DoubleClickTime => TouchDoubleClickTime;
         }
 
         public static void Register()

src/iOS/Avalonia.iOS/PlatformThreadingInterface.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Threading;
 using Avalonia.Platform;
 using Avalonia.Threading;
@@ -13,14 +12,14 @@ namespace Avalonia.iOS
         public static PlatformThreadingInterface Instance { get; } = new PlatformThreadingInterface();
         public bool CurrentThreadIsLoopThread => NSThread.Current.IsMainThread;
         
-        public event Action<DispatcherPriority?> Signaled;
+        public event System.Action<DispatcherPriority?> Signaled;
         public void RunLoop(CancellationToken cancellationToken)
         {
             //Mobile platforms are using external main loop
-            throw new NotSupportedException(); 
+            throw new System.NotSupportedException(); 
         }
         
-        public IDisposable StartTimer(DispatcherPriority priority, TimeSpan interval, Action tick)
+        public System.IDisposable StartTimer(DispatcherPriority priority, System.TimeSpan interval, System.Action tick)
             => NSTimer.CreateRepeatingScheduledTimer(interval, _ => tick());
 
         public void Signal(DispatcherPriority prio)
@@ -40,4 +39,4 @@ namespace Avalonia.iOS
             });
         }
     }
-}
+}

src/iOS/Avalonia.iOS/Stubs.cs

@@ -1,4 +1,3 @@
-using System;
 using System.IO;
 using Avalonia.Input;
 using Avalonia.Platform;
@@ -18,9 +17,9 @@ namespace Avalonia.iOS
 
     class WindowingPlatformStub : IWindowingPlatform
     {
-        public IWindowImpl CreateWindow() => throw new NotSupportedException();
+        public IWindowImpl CreateWindow() => throw new System.NotSupportedException();
 
-        public IWindowImpl CreateEmbeddableWindow() => throw new NotSupportedException();
+        public IWindowImpl CreateEmbeddableWindow() => throw new System.NotSupportedException();
 
         public ITrayIconImpl CreateTrayIcon() => null;
     }