Fix selection event generation in wxMac wxListBox

Prevents deselecting the selected item in single-selection listbox.

Also generate correct events in the multi-selection case by reusing the
existing wxListBoxBase::CalcAndSendEvent() method.

Closes #15603.

include/wx/osx/listbox.h

@@ -125,6 +125,12 @@ public:
     bool MacGetBlockEvents() const { return m_blockEvents; }
 
     virtual void HandleLineEvent( unsigned int n, bool doubleClick );
+
+    // These are called by wxNSTableView
+    using wxListBoxBase::DoChangeSingleSelection;
+    using wxListBoxBase::CalcAndSendEvent;
+    int GetOldSelection() const { return m_oldSelections.empty() ? wxNOT_FOUND : m_oldSelections[0]; }
+
 protected:
     // callback for derived classes which may have to insert additional data
     // at a certain line - which cannot be predetermined for sorted list data

src/osx/cocoa/listbox.mm

@@ -297,23 +297,33 @@ protected:
 
     int row = [self selectedRow];
 
-    if (row == -1) 
+    wxWidgetCocoaImpl* impl = (wxWidgetCocoaImpl* ) wxWidgetImpl::FindFromWXWidget( self );
-    {
+    wxListBox *list = static_cast<wxListBox*> ( impl->GetWXPeer());
-        // no row selected
+    wxCHECK_RET( list != NULL , wxT("Listbox expected"));
-    } 
-    else 
-    {
-        wxWidgetCocoaImpl* impl = (wxWidgetCocoaImpl* ) wxWidgetImpl::FindFromWXWidget( self );
-        wxListBox *list = static_cast<wxListBox*> ( impl->GetWXPeer());
-        wxCHECK_RET( list != NULL , wxT("Listbox expected"));
 
-        if ((row < 0) || (row > (int) list->GetCount()))  // OS X can select an item below the last item
+    // Correct notification events for multiselection list, like in Carbon version
+    if (list->HasMultipleSelection() && !list->MacGetBlockEvents())
+    {
+        list->CalcAndSendEvent();
+        return;
+    }
+
+    if ( !list->MacGetBlockEvents() )
+    {
+        // OS X can select an item below the last item. In that case keep the old selection because
+        // in wxWidgets API there is no notification event for removing the selection from a single-selection list box.
+        // Otherwise call DoChangeSingleSelection so GetOldSelection() will return the correct value if row < 0 later.
+        if ((row < 0) || (row > (int) list->GetCount()))
+        {
+            int oldsel = list->GetOldSelection();
+            if (oldsel >= 0)
+                list->SetSelection(oldsel);
             return;
-
+        }
-        if ( !list->MacGetBlockEvents() )
+        if ( !list->DoChangeSingleSelection(row) )
-            list->HandleLineEvent( row, false );
+            return ;
+        list->HandleLineEvent( row, false );
     }
-
 }
 
 - (void)setFont:(NSFont *)aFont