MacOS: Make sure macOS child window layer is not lower than parent window.

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

@@ -25,9 +25,14 @@ private:
     PopupImpl(IAvnWindowEvents* events) : TopLevelImpl(events), WindowBaseImpl(events)
     {
         WindowEvents = events;
-        [Window setLevel:NSPopUpMenuWindowLevel];
+        UpdateWindowLevel();
     }
 protected:
+    virtual NSWindowLevel GetBaseWindowLevel() override
+    {
+        return NSPopUpMenuWindowLevel;
+    }
+
     virtual NSWindowStyleMask CalculateStyleMask() override
     {
         return NSWindowStyleMaskBorderless;

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

@@ -80,8 +80,12 @@ public:
     virtual bool CanZoom() { return false; }
                            
     virtual HRESULT SetParent(IAvnWindowBase* parent) override;
-                           
+
+    void UpdateWindowLevel();
+
 protected:
+    virtual NSWindowLevel GetBaseWindowLevel();
+
     virtual NSWindowStyleMask CalculateStyleMask() = 0;
     virtual void UpdateAppearance() override;
     virtual void SetClientSize(NSSize size) override;
@@ -101,6 +105,7 @@ protected:
     AutoFitContentView *StandardContainer;
     AvnPoint lastPositionSet;
     bool _shown;
+    bool _isTopmost = false;
     std::list<ComObjectWeakPtr<WindowBaseImpl>> _children;
 
 public:

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

@@ -18,6 +18,7 @@
 #include "WindowImpl.h"
 #include "AvnTextInputMethod.h"
 #include "AvnView.h"
+#include <algorithm>
 
 @class AutoFitContentView;
 
@@ -206,12 +207,41 @@ HRESULT WindowBaseImpl::SetTopMost(bool value) {
     START_COM_CALL;
 
     @autoreleasepool {
-        [Window setLevel:value ? NSFloatingWindowLevel : NSNormalWindowLevel];
+        _isTopmost = value;
+
+        UpdateWindowLevel();
 
         return S_OK;
     }
 }
 
+NSWindowLevel WindowBaseImpl::GetBaseWindowLevel() {
+    return _isTopmost ? NSFloatingWindowLevel : NSNormalWindowLevel;
+}
+
+void WindowBaseImpl::UpdateWindowLevel() {
+    if (Window == nullptr)
+        return;
+
+    auto level = GetBaseWindowLevel();
+
+    // An owned window must be able to come to the front of its owner.
+    // TODO: It shouldn't be necessary if we used `addChildWindow` API.
+    auto parent = Parent.tryGet();
+
+    if (parent != nullptr && parent->Window != nullptr)
+        level = std::max(level, [parent->Window level]);
+
+    [Window setLevel:level];
+
+    for (auto iterator = _children.begin(); iterator != _children.end(); iterator++) {
+        auto child = (*iterator).tryGet();
+
+        if (child != nullptr)
+            child->UpdateWindowLevel();
+    }
+}
+
 HRESULT WindowBaseImpl::Close() {
     START_COM_CALL;
 
@@ -527,6 +557,8 @@ HRESULT WindowBaseImpl::SetParent(IAvnWindowBase *parent) {
             UpdateAppearance();
         }
 
+        UpdateWindowLevel();
+
         return S_OK;
     }
 }