Allow wxDataViewCtrl to gain focus in wxOSX

Fix numerous focus-handling bugs in wxOSX in combination with
NSScrollView (which cannot get focus by itself and which was already
treated specially in many, but not all, places), including

- inability to set the focus
- loss of wxEVT_SET_FOCUS events
- loss of wxWindow<->NSView association after clearing wxDVC columns

src/osx/cocoa/dataview.mm

@@ -1915,6 +1915,14 @@ outlineView:(NSOutlineView*)outlineView
     }
 }
 
+-(BOOL) becomeFirstResponder
+{
+    BOOL r = [super becomeFirstResponder];
+    if ( r )
+        implementation->DoNotifyFocusSet();
+    return r;
+}
+
 @end
 
 // ============================================================================
@@ -1942,15 +1950,16 @@ wxCocoaDataViewControl::wxCocoaDataViewControl(wxWindow* peer,
     [scrollview setAutohidesScrollers:YES];
     [scrollview setDocumentView:m_OutlineView];
 
-    // we cannot call InstallHandler(m_OutlineView) here, because we are handling
-    // our action:s ourselves, only associate the view with this impl
-    Associate(m_OutlineView,this);
     // initialize the native control itself too
     InitOutlineView(style);
 }
 
 void wxCocoaDataViewControl::InitOutlineView(long style)
 {
+    // we cannot call InstallHandler(m_OutlineView) here, because we are handling
+    // our action:s ourselves, only associate the view with this impl
+    Associate(m_OutlineView,this);
+
     [m_OutlineView setImplementation:this];
     [m_OutlineView setFocusRingType:NSFocusRingTypeNone];
     [m_OutlineView setColumnAutoresizingStyle:NSTableViewLastColumnOnlyAutoresizingStyle];

src/osx/cocoa/window.mm

@@ -2328,12 +2328,18 @@ bool wxWidgetCocoaImpl::GetNeedsDisplay() const
 
 bool wxWidgetCocoaImpl::CanFocus() const
 {
-    return [m_osxView canBecomeKeyView] == YES;
+    NSView* targetView = m_osxView;
+    if ( [m_osxView isKindOfClass:[NSScrollView class] ] )
+        targetView = [(NSScrollView*) m_osxView documentView];
+    return [targetView canBecomeKeyView] == YES;
 }
 
 bool wxWidgetCocoaImpl::HasFocus() const
 {
-    return ( FindFocus() == m_osxView );
+    NSView* targetView = m_osxView;
+    if ( [m_osxView isKindOfClass:[NSScrollView class] ] )
+        targetView = [(NSScrollView*) m_osxView documentView];
+    return ( FindFocus() == targetView );
 }
 
 bool wxWidgetCocoaImpl::SetFocus()
@@ -2341,6 +2347,10 @@ bool wxWidgetCocoaImpl::SetFocus()
     if ( !CanFocus() )
         return false;
 
+    NSView* targetView = m_osxView;
+    if ( [m_osxView isKindOfClass:[NSScrollView class] ] )
+        targetView = [(NSScrollView*) m_osxView documentView];
+
     // TODO remove if no issues arise: should not raise the window, only assign focus
     //[[m_osxView window] makeKeyAndOrderFront:nil] ;
     [[m_osxView window] makeFirstResponder: m_osxView] ;