Add an interface for creation of QgsLayoutView context menus

Allows display of custom right click menus when right click
events are not handled by the current layout view tool.

python/gui/layout/qgslayoutview.sip

@@ -90,6 +90,19 @@ class QgsLayoutView: QGraphicsView
 .. seealso:: setHorizontalRuler()
 %End
 
+    void setMenuProvider( QgsLayoutViewMenuProvider *provider /Transfer/ );
+%Docstring
+ Sets a ``provider`` for context menus. Ownership of the provider is transferred to the view.
+.. seealso:: menuProvider()
+%End
+
+    QgsLayoutViewMenuProvider *menuProvider() const;
+%Docstring
+ Returns the provider for context menus. Returned value may be None if no provider is set.
+.. seealso:: setMenuProvider()
+ :rtype: QgsLayoutViewMenuProvider
+%End
+
   public slots:
 
     void zoomFull();
@@ -191,6 +204,33 @@ class QgsLayoutView: QGraphicsView
 
 };
 
+
+class QgsLayoutViewMenuProvider
+{
+%Docstring
+
+ Interface for a QgsLayoutView context menu.
+
+ Implementations of this interface can be made to allow QgsLayoutView
+ instances to provide custom context menus (opened upon right-click).
+
+.. seealso:: QgsLayoutView
+.. versionadded:: 3.0
+%End
+
+%TypeHeaderCode
+#include "qgslayoutview.h"
+%End
+  public:
+    virtual ~QgsLayoutViewMenuProvider();
+
+    virtual QMenu *createContextMenu( QWidget *parent /Transfer/, QgsLayout *layout, QPointF layoutPoint ) const = 0 /Factory/;
+%Docstring
+Return a newly created menu instance (or null pointer on error)
+ :rtype: QMenu
+%End
+};
+
 /************************************************************************
  * This file has been generated automatically from                      *
  *                                                                      *

src/gui/layout/qgslayoutview.cpp

@@ -28,6 +28,7 @@
 #include "qgsapplication.h"
 #include <memory>
 #include <QDesktopWidget>
+#include <QMenu>
 
 #define MIN_VIEW_SCALE 0.05
 #define MAX_VIEW_SCALE 1000.0
@@ -139,6 +140,16 @@ void QgsLayoutView::setVerticalRuler( QgsLayoutRuler *ruler )
   updateRulers();
 }
 
+void QgsLayoutView::setMenuProvider( QgsLayoutViewMenuProvider *provider )
+{
+  mMenuProvider.reset( provider );
+}
+
+QgsLayoutViewMenuProvider *QgsLayoutView::menuProvider() const
+{
+  return mMenuProvider.get();
+}
+
 void QgsLayoutView::zoomFull()
 {
   fitInView( scene()->sceneRect(), Qt::KeepAspectRatio );
@@ -205,6 +216,15 @@ void QgsLayoutView::mousePressEvent( QMouseEvent *event )
       setTool( mMidMouseButtonPanTool );
       event->accept();
     }
+    else if ( event->button() == Qt::RightButton && mMenuProvider )
+    {
+      QMenu *menu = mMenuProvider->createContextMenu( this, currentLayout(), mapToScene( event->pos() ) );
+      if ( menu )
+      {
+        menu->exec( event->globalPos() );
+        delete menu;
+      }
+    }
     else
     {
       QGraphicsView::mousePressEvent( event );

src/gui/layout/qgslayoutview.h

@@ -22,13 +22,16 @@
 #include "qgis_gui.h"
 #include <QPointer>
 #include <QGraphicsView>
+#include <memory>
 
+class QMenu;
 class QgsLayout;
 class QgsLayoutViewTool;
 class QgsLayoutViewToolTemporaryKeyPan;
 class QgsLayoutViewToolTemporaryKeyZoom;
 class QgsLayoutViewToolTemporaryMousePan;
 class QgsLayoutRuler;
+class QgsLayoutViewMenuProvider;
 
 /**
  * \ingroup gui
@@ -112,6 +115,18 @@ class GUI_EXPORT QgsLayoutView: public QGraphicsView
      */
     void setVerticalRuler( QgsLayoutRuler *ruler );
 
+    /**
+     * Sets a \a provider for context menus. Ownership of the provider is transferred to the view.
+     * \see menuProvider()
+     */
+    void setMenuProvider( QgsLayoutViewMenuProvider *provider SIP_TRANSFER );
+
+    /**
+    * Returns the provider for context menus. Returned value may be nullptr if no provider is set.
+    * \see setMenuProvider()
+    */
+    QgsLayoutViewMenuProvider *menuProvider() const;
+
   public slots:
 
     /**
@@ -228,9 +243,31 @@ class GUI_EXPORT QgsLayoutView: public QGraphicsView
 
     QgsLayoutRuler *mHorizontalRuler = nullptr;
     QgsLayoutRuler *mVerticalRuler = nullptr;
+    std::unique_ptr< QgsLayoutViewMenuProvider > mMenuProvider;
 
     friend class TestQgsLayoutView;
 
 };
 
+
+/**
+ * \ingroup gui
+ *
+ * Interface for a QgsLayoutView context menu.
+ *
+ * Implementations of this interface can be made to allow QgsLayoutView
+ * instances to provide custom context menus (opened upon right-click).
+ *
+ * \see QgsLayoutView
+ * \since QGIS 3.0
+ */
+class GUI_EXPORT QgsLayoutViewMenuProvider
+{
+  public:
+    virtual ~QgsLayoutViewMenuProvider() = default;
+
+    //! Return a newly created menu instance (or null pointer on error)
+    virtual QMenu *createContextMenu( QWidget *parent SIP_TRANSFER, QgsLayout *layout, QPointF layoutPoint ) const = 0 SIP_FACTORY;
+};
+
 #endif // QGSLAYOUTVIEW_H