[OSX] programatically implement child window relationship

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

@@ -300,6 +300,11 @@
 
 - (void)mouseDown:(NSEvent *)event
 {
+    if(_parent != nullptr)
+    {
+        _parent->BringToFront();
+    }
+    
     _isLeftPressed = true;
     _lastMouseDownEvent = event;
     [self mouseEvent:event withType:LeftButtonDown];

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

@@ -183,6 +183,11 @@
     return self;
 }
 
+- (void)mouseDown:(NSEvent *)event
+{
+    _parent->BringToFront();
+}
+
 - (BOOL)windowShouldClose:(NSWindow *)sender
 {
     auto window = dynamic_cast<WindowImpl*>(_parent.getRaw());
@@ -209,7 +214,14 @@
     {
         ComPtr<WindowBaseImpl> parent = _parent;
         _parent = NULL;
-        [self restoreParentWindow];
+        
+        auto window = dynamic_cast<WindowImpl*>(parent.getRaw());
+        
+        if(window != nullptr)
+        {
+            window->SetParent(nullptr);
+        }
+        
         parent->BaseEvents->Closed();
         [parent->View onClosed];
     }
@@ -220,17 +232,11 @@
     if(_canBecomeKeyWindow)
     {
         // If the window has a child window being shown as a dialog then don't allow it to become the key window.
-        for(NSWindow* uch in [self childWindows])
+        auto parent = dynamic_cast<WindowImpl*>(_parent.getRaw());
+        
+        if(parent != nullptr)
         {
-            if (![uch conformsToProtocol:@protocol(AvnWindowProtocol)])
-            {
-                continue;
-            }
-
-            id <AvnWindowProtocol> ch = (id <AvnWindowProtocol>) uch;
-
-            if(ch.isDialog)
-                return false;
+            return parent->CanBecomeKeyWindow();
         }
 
         return true;
@@ -273,16 +279,6 @@
     [super becomeKeyWindow];
 }
 
--(void) restoreParentWindow;
-{
-    auto parent = [self parentWindow];
-
-    if(parent != nil)
-    {
-        [parent removeChildWindow:self];
-    }
-}
-
 - (void)windowDidMiniaturize:(NSNotification *)notification
 {
     auto parent = dynamic_cast<IWindowStateChanged*>(_parent.operator->());

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

@@ -99,6 +99,8 @@ BEGIN_INTERFACE_MAP()
     virtual bool IsDialog();
 
     id<AvnWindowProtocol> GetWindowProtocol ();
+                           
+    virtual void BringToFront ();
 
 protected:
     virtual NSWindowStyleMask GetStyle();

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

@@ -143,8 +143,6 @@ HRESULT WindowBaseImpl::Hide() {
     @autoreleasepool {
         if (Window != nullptr) {
             [Window orderOut:Window];
-
-            [GetWindowProtocol() restoreParentWindow];
         }
 
         return S_OK;
@@ -610,6 +608,11 @@ id <AvnWindowProtocol> WindowBaseImpl::GetWindowProtocol() {
     return (id <AvnWindowProtocol>) Window;
 }
 
+void WindowBaseImpl::BringToFront()
+{
+    // do nothing.
+}
+
 extern IAvnWindow* CreateAvnWindow(IAvnWindowEvents*events, IAvnGlContext* gl)
 {
     @autoreleasepool

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

@@ -8,6 +8,7 @@
 
 #import "WindowBaseImpl.h"
 #include "IWindowStateChanged.h"
+#include <list>
 
 class WindowImpl : public virtual WindowBaseImpl, public virtual IAvnWindow, public IWindowStateChanged
 {
@@ -22,7 +23,8 @@ private:
     bool _transitioningWindowState;
     bool _isClientAreaExtended;
     bool _isDialog;
-    WindowImpl* _lastParent;
+    WindowImpl* _parent;
+    std::list<WindowImpl*> _children;
     AvnExtendClientAreaChromeHints _extendClientHints;
 
     FORWARD_IUNKNOWN()
@@ -91,6 +93,10 @@ BEGIN_INTERFACE_MAP()
     virtual bool IsDialog() override;
     
     virtual void OnInitialiseNSWindow() override;
+    
+    virtual void BringToFront () override;
+    
+    bool CanBecomeKeyWindow ();
 
 protected:
     virtual NSWindowStyleMask GetStyle() override;

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

@@ -10,6 +10,7 @@
 #include "WindowProtocol.h"
 
 WindowImpl::WindowImpl(IAvnWindowEvents *events, IAvnGlContext *gl) : WindowBaseImpl(events, gl) {
+    _children = std::list<WindowImpl*>();
     _isClientAreaExtended = false;
     _extendClientHints = AvnDefaultChrome;
     _fullScreenActive = false;
@@ -20,7 +21,7 @@ WindowImpl::WindowImpl(IAvnWindowEvents *events, IAvnGlContext *gl) : WindowBase
     _lastWindowState = Normal;
     _actualWindowState = Normal;
     _lastTitle = @"";
-    _lastParent = nullptr;
+    _parent = nullptr;
     WindowEvents = events;
 }
 
@@ -63,9 +64,9 @@ void WindowImpl::OnInitialiseNSWindow(){
         SetExtendClientArea(true);
     }
     
-    if(_lastParent != nullptr)
+    if(_parent != nullptr)
     {
-        SetParent(_lastParent);
+        SetParent(_parent);
     }
 }
 
@@ -96,33 +97,56 @@ HRESULT WindowImpl::SetParent(IAvnWindow *parent) {
     START_COM_CALL;
 
     @autoreleasepool {
-        if (parent == nullptr)
-            return E_POINTER;
+        if(_parent != nullptr)
+        {
+            _parent->_children.remove(this);
+        }
 
         auto cparent = dynamic_cast<WindowImpl *>(parent);
-        if (cparent == nullptr)
-            return E_INVALIDARG;
-
         
-        _lastParent = cparent;
+        _parent = cparent;
         
-        if(Window != nullptr){
-        // If one tries to show a child window with a minimized parent window, then the parent window will be
-        // restored but macOS isn't kind enough to *tell* us that, so the window will be left in a non-interactive
-        // state. Detect this and explicitly restore the parent window ourselves to avoid this situation.
-        if (cparent->WindowState() == Minimized)
-            cparent->SetWindowState(Normal);
-
-        [Window setCollectionBehavior:NSWindowCollectionBehaviorFullScreenAuxiliary];
-        [cparent->Window addChildWindow:Window ordered:NSWindowAbove];
-
-        UpdateStyle();
+        if(_parent != nullptr && Window != nullptr){
+            // If one tries to show a child window with a minimized parent window, then the parent window will be
+            // restored but macOS isn't kind enough to *tell* us that, so the window will be left in a non-interactive
+            // state. Detect this and explicitly restore the parent window ourselves to avoid this situation.
+            if (cparent->WindowState() == Minimized)
+                cparent->SetWindowState(Normal);
+
+            [Window setCollectionBehavior:NSWindowCollectionBehaviorFullScreenAuxiliary];
+                
+            cparent->_children.push_back(this);
+                
+            UpdateStyle();
         }
 
         return S_OK;
     }
 }
 
+void WindowImpl::BringToFront()
+{
+    Activate();
+    
+    for(auto iterator = _children.begin(); iterator != _children.end(); iterator++)
+    {
+        (*iterator)->BringToFront();
+    }
+}
+
+bool WindowImpl::CanBecomeKeyWindow()
+{
+    for(auto iterator = _children.begin(); iterator != _children.end(); iterator++)
+    {
+        if((*iterator)->IsDialog())
+        {
+            return false;
+        }
+    }
+    
+    return true;
+}
+
 void WindowImpl::StartStateTransition() {
     _transitioningWindowState = true;
 }
@@ -534,7 +558,7 @@ bool WindowImpl::IsDialog() {
 }
 
 NSWindowStyleMask WindowImpl::GetStyle() {
-    unsigned long s = this->_isDialog ? NSWindowStyleMaskDocModalWindow : NSWindowStyleMaskBorderless;
+    unsigned long s = NSWindowStyleMaskBorderless;
 
     switch (_decorations) {
         case SystemDecorationsNone:

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

@@ -11,7 +11,6 @@
 
 @protocol AvnWindowProtocol
 -(void) pollModalSession: (NSModalSession _Nonnull) session;
--(void) restoreParentWindow;
 -(bool) shouldTryToHandleEvents;
 -(void) setEnabled: (bool) enable;
 -(void) showAppMenuOnly;