Port selection handling code from composer

python/core/layout/qgslayout.sip

@@ -75,6 +75,19 @@ class QgsLayout : QGraphicsScene, QgsExpressionContextGenerator, QgsLayoutUndoOb
  :rtype: list of QgsLayoutItem
 %End
 
+    void setSelectedItem( QgsLayoutItem *item );
+%Docstring
+ Clears any selected items and sets ``item`` as the current selection.
+%End
+
+    void deselectAll();
+%Docstring
+ Clears any selected items in the layout.
+
+ Call this method rather than QGraphicsScene.clearSelection, as the latter does
+ not correctly emit signals to allow the layout's model to update.
+%End
+
     QgsLayoutItem *itemByUuid( const QString &uuid );
 %Docstring
  Returns the layout item with matching ``uuid`` unique identifier, or a None
@@ -302,6 +315,12 @@ class QgsLayout : QGraphicsScene, QgsExpressionContextGenerator, QgsLayoutUndoOb
  Emitted whenever the expression variables stored in the layout have been changed.
 %End
 
+    void selectedItemChanged( QgsLayoutItem *selected );
+%Docstring
+ Emitted whenever the selected item changes.
+ If None, no item is selected.
+%End
+
 };
 
 

src/core/layout/qgslayout.cpp

@@ -63,6 +63,33 @@ QList<QgsLayoutItem *> QgsLayout::selectedLayoutItems( const bool includeLockedI
   return layoutItemList;
 }
 
+void QgsLayout::setSelectedItem( QgsLayoutItem *item )
+{
+  whileBlocking( this )->deselectAll();
+  if ( item )
+  {
+    item->setSelected( true );
+  }
+  emit selectedItemChanged( item );
+}
+
+void QgsLayout::deselectAll()
+{
+  //we can't use QGraphicsScene::clearSelection, as that emits no signals
+  //and we don't know which items are being deselected
+  //accordingly, we can't inform the layout model of selection changes
+  //instead, do the clear selection manually...
+  const QList<QGraphicsItem *> selectedItemList = selectedItems();
+  for ( QGraphicsItem *item : selectedItemList )
+  {
+    if ( QgsLayoutItem *layoutItem = dynamic_cast<QgsLayoutItem *>( item ) )
+    {
+      layoutItem->setSelected( false );
+    }
+  }
+  emit selectedItemChanged( nullptr );
+}
+
 QgsLayoutItem *QgsLayout::itemByUuid( const QString &uuid )
 {
   QList<QgsLayoutItem *> itemList;

src/core/layout/qgslayout.h

@@ -112,6 +112,19 @@ class CORE_EXPORT QgsLayout : public QGraphicsScene, public QgsExpressionContext
      */
     QList<QgsLayoutItem *> selectedLayoutItems( const bool includeLockedItems = true );
 
+    /**
+     * Clears any selected items and sets \a item as the current selection.
+    */
+    void setSelectedItem( QgsLayoutItem *item );
+
+    /**
+     * Clears any selected items in the layout.
+     *
+     * Call this method rather than QGraphicsScene::clearSelection, as the latter does
+     * not correctly emit signals to allow the layout's model to update.
+    */
+    void deselectAll();
+
     /**
      * Returns the layout item with matching \a uuid unique identifier, or a nullptr
      * if a matching item could not be found.
@@ -358,6 +371,12 @@ class CORE_EXPORT QgsLayout : public QGraphicsScene, public QgsExpressionContext
      */
     void variablesChanged();
 
+    /**
+     * Emitted whenever the selected item changes.
+     * If nullptr, no item is selected.
+     */
+    void selectedItemChanged( QgsLayoutItem *selected );
+
   private:
 
     QgsProject *mProject = nullptr;

tests/src/python/test_qgslayout.py

@@ -102,6 +102,44 @@ def testSelectedItems(self):
         self.assertEqual(set(l.selectedLayoutItems(False)), set([item1, item2]))
         self.assertEqual(set(l.selectedLayoutItems(True)), set([item1, item2, item3]))
 
+    def testSelections(self):
+        p = QgsProject()
+        l = QgsLayout(p)
+
+        # add some items
+        item1 = QgsLayoutItemMap(l)
+        l.addItem(item1)
+        item2 = QgsLayoutItemMap(l)
+        l.addItem(item2)
+        item3 = QgsLayoutItemMap(l)
+        l.addItem(item3)
+
+        select_changed_spy = QSignalSpy(l.selectedItemChanged)
+        l.setSelectedItem(None)
+        self.assertFalse(l.selectedLayoutItems())
+        self.assertEqual(len(select_changed_spy), 1)
+        self.assertEqual(select_changed_spy[-1][0], None)
+
+        l.setSelectedItem(item1)
+        self.assertEqual(l.selectedLayoutItems(), [item1])
+        self.assertEqual(len(select_changed_spy), 2)
+        self.assertEqual(select_changed_spy[-1][0], item1)
+
+        l.setSelectedItem(None)
+        self.assertFalse(l.selectedLayoutItems())
+        self.assertEqual(len(select_changed_spy), 3)
+        self.assertEqual(select_changed_spy[-1][0], None)
+
+        l.setSelectedItem(item2)
+        self.assertEqual(l.selectedLayoutItems(), [item2])
+        self.assertEqual(len(select_changed_spy), 4)
+        self.assertEqual(select_changed_spy[-1][0], item2)
+
+        l.deselectAll()
+        self.assertFalse(l.selectedLayoutItems())
+        self.assertEqual(len(select_changed_spy), 5)
+        self.assertEqual(select_changed_spy[-1][0], None)
+
 
 if __name__ == '__main__':
     unittest.main()