Fix wxRadioButton grouping in wxQt

Create QButtonGroup as needed to honour wxRB_GROUP and wxRB_SINGLE
styles.

Co-Authored-By: Cătălin Răceanu <maildus@gmail.com>

Co-Authored-By: liamtreacy <liam.treacy@gmail.com>

src/qt/radiobut.cpp

@@ -12,6 +12,53 @@
 #include "wx/qt/private/converter.h"
 
 #include <QtWidgets/QRadioButton>
+#include <QtWidgets/QButtonGroup>
+
+namespace
+{
+
+// Tiny helper applying a safe cast to return the handle of wxRadioButton as
+// its actual type.
+inline
+QRadioButton* QtGetRadioButton(wxRadioButton* radioBtn)
+{
+    return static_cast<QRadioButton*>(radioBtn->GetHandle());
+}
+
+void QtStartNewGroup(QRadioButton* qtRadioButton)
+{
+    // Note that the QButtonGroup created here will be deallocated when its
+    // parent // QRadioButton is destroyed.
+    QButtonGroup* qtButtonGroup = new QButtonGroup(qtRadioButton);
+    qtButtonGroup->addButton(qtRadioButton);
+}
+
+bool QtTryJoiningExistingGroup(wxRadioButton* radioBtnThis)
+{
+    for ( wxWindow* previous = radioBtnThis->GetPrevSibling();
+          previous;
+          previous = previous->GetPrevSibling() )
+    {
+        if ( wxRadioButton* radioBtn = wxDynamicCast(previous, wxRadioButton) )
+        {
+            // We should never join the exclusive group of wxRB_SINGLE button.
+            if ( !radioBtn->HasFlag(wxRB_SINGLE) )
+            {
+                if ( QButtonGroup *qtGroup = QtGetRadioButton(radioBtn)->group() )
+                {
+                    qtGroup->addButton(QtGetRadioButton(radioBtnThis));
+                    return true;
+                }
+            }
+
+            break;
+        }
+    }
+
+    return false;
+}
+
+} // anonymous namespace
 
 wxRadioButton::wxRadioButton() :
     m_qtRadioButton(NULL)
@@ -42,7 +89,27 @@ bool wxRadioButton::Create( wxWindow *parent,
     m_qtRadioButton = new QRadioButton( parent->GetHandle() );
     m_qtRadioButton->setText( wxQtConvertString( label ));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    if ( !QtCreateControl(parent, id, pos, size, style, validator, name) )
+        return false;
+
+    // Check if we need to create a new button group: this must be done when
+    // explicitly requested to do so (wxRB_GROUP) but also for wxRB_SINGLE
+    // buttons to prevent them implicitly becoming part of an existing group.
+    if ( (style & wxRB_GROUP) || (style & wxRB_SINGLE) )
+    {
+        QtStartNewGroup(m_qtRadioButton);
+    }
+    else
+    {
+        // Otherwise try to join an already existing group. Currently we don't
+        // do anything if joining it fails, i.e. if there is no current group
+        // yet, because the radio buttons not explicitly associated with some
+        // group still work as if they were part of one, so we just ignore the
+        // return value of this function.
+        QtTryJoiningExistingGroup(this);
+    }
+
+    return true;
 }
 
 void wxRadioButton::SetValue(bool value)