only create the NSWindow when show is called. Cache sizes until needed.

native/Avalonia.Native/src/OSX/WindowBaseImpl.h

@@ -24,10 +24,7 @@ BEGIN_INTERFACE_MAP()
         INTERFACE_MAP_ENTRY(IAvnWindowBase, IID_IAvnWindowBase)
     END_INTERFACE_MAP()
 
-    virtual ~WindowBaseImpl() {
-        View = NULL;
-        Window = NULL;
-    }
+    virtual ~WindowBaseImpl();
 
     AutoFitContentView *StandardContainer;
     AvnView *View;
@@ -36,6 +33,9 @@ BEGIN_INTERFACE_MAP()
     ComPtr<IAvnGlContext> _glContext;
     NSObject <IRenderTarget> *renderTarget;
     AvnPoint lastPositionSet;
+    NSSize lastSize;
+    NSSize lastMinSize;
+    NSSize lastMaxSize;
     NSString *_lastTitle;
 
     bool _shown;
@@ -116,6 +116,9 @@ protected:
 
     void UpdateStyle();
 
+private:
+    void InitialiseNSWindow ();
+
 };
 
 #endif //AVALONIA_NATIVE_OSX_WINDOWBASEIMPL_H

native/Avalonia.Native/src/OSX/WindowBaseImpl.mm

@@ -12,6 +12,13 @@
 #import "cursor.h"
 #include "ResizeScope.h"
 #import "AutoFitContentView.h"
+#include "WindowBaseImpl.h"
+
+
+WindowBaseImpl::~WindowBaseImpl() {
+    View = nullptr;
+    Window = nullptr;
+}
 
 WindowBaseImpl::WindowBaseImpl(IAvnWindowBaseEvents *events, IAvnGlContext *gl) {
     _shown = false;
@@ -22,17 +29,11 @@ WindowBaseImpl::WindowBaseImpl(IAvnWindowBaseEvents *events, IAvnGlContext *gl)
     View = [[AvnView alloc] initWithParent:this];
     StandardContainer = [[AutoFitContentView new] initWithContent:View];
 
-    Window = [[AvnWindow alloc] initWithParent:this];
-    [Window setContentView:StandardContainer];
-
     lastPositionSet.X = 100;
     lastPositionSet.Y = 100;
     _lastTitle = @"";
 
-    [Window setStyleMask:NSWindowStyleMaskBorderless];
-    [Window setBackingType:NSBackingStoreBuffered];
-
-    [Window setOpaque:false];
+    Window = nullptr;
 }
 
 HRESULT WindowBaseImpl::ObtainNSViewHandle(void **ret) {
@@ -83,6 +84,8 @@ HRESULT WindowBaseImpl::Show(bool activate, bool isDialog) {
     START_COM_CALL;
 
     @autoreleasepool {
+        InitialiseNSWindow();
+
         SetPosition(lastPositionSet);
         UpdateStyle();
 
@@ -97,6 +100,10 @@ HRESULT WindowBaseImpl::Show(bool activate, bool isDialog) {
             [Window orderFront:Window];
         }
 
+        [Window setContentMinSize:lastMinSize];
+        [Window setContentMaxSize:lastMaxSize];
+        [Window setContentSize: lastSize];
+
         _shown = true;
 
         return S_OK;
@@ -225,8 +232,13 @@ HRESULT WindowBaseImpl::SetMinMaxSize(AvnSize minSize, AvnSize maxSize) {
     START_COM_CALL;
 
     @autoreleasepool {
-        [Window setMinSize:ToNSSize(minSize)];
-        [Window setMaxSize:ToNSSize(maxSize)];
+        lastMinSize = ToNSSize(minSize);
+        lastMaxSize = ToNSSize(maxSize);
+
+        if(Window != nullptr) {
+            [Window setContentMinSize:lastMinSize];
+            [Window setContentMaxSize:lastMaxSize];
+        }
 
         return S_OK;
     }
@@ -243,8 +255,8 @@ HRESULT WindowBaseImpl::Resize(double x, double y, AvnPlatformResizeReason reaso
     auto resizeBlock = ResizeScope(View, reason);
 
     @autoreleasepool {
-        auto maxSize = [Window maxSize];
-        auto minSize = [Window minSize];
+        auto maxSize = lastMaxSize;
+        auto minSize = lastMinSize;
 
         if (x < minSize.width) {
             x = minSize.width;
@@ -267,8 +279,12 @@ HRESULT WindowBaseImpl::Resize(double x, double y, AvnPlatformResizeReason reaso
                 BaseEvents->Resized(AvnSize{x, y}, reason);
             }
 
-            [Window setContentSize:NSSize{x, y}];
-            [Window invalidateShadow];
+            lastSize = NSSize {x, y};
+
+            if(Window != nullptr) {
+                [Window setContentSize:lastSize];
+                [Window invalidateShadow];
+            }
         }
         @finally {
             _inResize = false;
@@ -502,4 +518,13 @@ NSWindowStyleMask WindowBaseImpl::GetStyle() {
 
 void WindowBaseImpl::UpdateStyle() {
     [Window setStyleMask:GetStyle()];
-}
+}
+
+void WindowBaseImpl::InitialiseNSWindow() {
+    Window = [[AvnWindow alloc] initWithParent:this contentRect:NSRect{ 0, 0, lastSize } styleMask:GetStyle()];
+    [Window setContentView:StandardContainer];
+    [Window setStyleMask:NSWindowStyleMaskBorderless];
+    [Window setBackingType:NSBackingStoreBuffered];
+
+    [Window setOpaque:false];
+}

native/Avalonia.Native/src/OSX/window.h

@@ -8,7 +8,7 @@
 class WindowBaseImpl;
 
 @interface AvnWindow : NSWindow <NSWindowDelegate>
--(AvnWindow* _Nonnull) initWithParent: (WindowBaseImpl* _Nonnull) parent;
+-(AvnWindow* _Nonnull) initWithParent: (WindowBaseImpl* _Nonnull) parent contentRect: (NSRect)contentRect styleMask: (NSWindowStyleMask)styleMask;
 -(void) setCanBecomeKeyAndMain;
 -(void) pollModalSession: (NSModalSession _Nonnull) session;
 -(void) restoreParentWindow;

native/Avalonia.Native/src/OSX/window.mm

@@ -143,9 +143,10 @@
     _canBecomeKeyAndMain = true;
 }
 
--(AvnWindow*)  initWithParent: (WindowBaseImpl*) parent
+-(AvnWindow*)  initWithParent: (WindowBaseImpl*) parent contentRect: (NSRect)contentRect styleMask: (NSWindowStyleMask)styleMask;
 {
-    self = [super init];
+    self = [super initWithContentRect:contentRect styleMask: styleMask backing:NSBackingStoreBuffered defer:false];
+    
     [self setReleasedWhenClosed:false];
     _parent = parent;
     [self setDelegate:self];
@@ -155,6 +156,7 @@
     [self backingScaleFactor];
     [self setOpaque:NO];
     [self setBackgroundColor: [NSColor clearColor]];
+
     _isExtended = false;
     return self;
 }