Add signal when page is about to be deleted

Author: nyalldawson

python/core/layout/qgslayoutpagecollection.sip

@@ -225,6 +225,14 @@ class QgsLayoutPageCollection : QObject
  Emitted when pages are added or removed from the collection.
 %End
 
+    void pageAboutToBeRemoved( int pageNumber );
+%Docstring
+ Emitted just before a page is removed from the collection.
+
+ Page numbers in collections begin at 0 - so a page number of 0 indicates the
+ first page.
+%End
+
 };
 
 /************************************************************************

src/core/layout/qgslayoutpagecollection.cpp

@@ -221,6 +221,7 @@ void QgsLayoutPageCollection::deletePage( int pageNumber )
   if ( pageNumber < 0 || pageNumber >= mPages.count() )
     return;
 
+  emit pageAboutToBeRemoved( pageNumber );
   QgsLayoutItemPage *page = mPages.takeAt( pageNumber );
   mLayout->removeItem( page );
   page->deleteLater();
@@ -232,6 +233,7 @@ void QgsLayoutPageCollection::deletePage( QgsLayoutItemPage *page )
   if ( !mPages.contains( page ) )
     return;
 
+  emit pageAboutToBeRemoved( mPages.indexOf( page ) );
   mPages.removeAll( page );
   page->deleteLater();
   reflow();

src/core/layout/qgslayoutpagecollection.h

@@ -225,6 +225,14 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      */
     void changed();
 
+    /**
+     * Emitted just before a page is removed from the collection.
+     *
+     * Page numbers in collections begin at 0 - so a page number of 0 indicates the
+     * first page.
+     */
+    void pageAboutToBeRemoved( int pageNumber );
+
   private:
 
     QgsLayout *mLayout = nullptr;

tests/src/python/test_qgslayoutpagecollection.py

@@ -26,6 +26,7 @@
                        QgsSimpleFillSymbolLayer,
                        QgsFillSymbol)
 from qgis.PyQt.QtCore import Qt, QCoreApplication, QEvent, QPointF, QRectF
+from qgis.PyQt.QtTest import QSignalSpy
 
 from qgis.testing import start_app, unittest
 
@@ -152,28 +153,36 @@ def testDeletePages(self):
         page2.setPageSize('A5')
         collection.addPage(page2)
 
+        page_about_to_be_removed_spy = QSignalSpy(collection.pageAboutToBeRemoved)
+
         # delete page
         collection.deletePage(None)
         self.assertEqual(collection.pageCount(), 2)
+        self.assertEqual(len(page_about_to_be_removed_spy), 0)
 
         page3 = QgsLayoutItemPage(l)
         # try deleting a page not in collection
         collection.deletePage(page3)
         QCoreApplication.sendPostedEvents(None, QEvent.DeferredDelete)
         self.assertFalse(sip.isdeleted(page3))
         self.assertEqual(collection.pageCount(), 2)
+        self.assertEqual(len(page_about_to_be_removed_spy), 0)
 
         collection.deletePage(page)
         self.assertEqual(collection.pageCount(), 1)
         self.assertFalse(page in collection.pages())
         QCoreApplication.sendPostedEvents(None, QEvent.DeferredDelete)
         self.assertTrue(sip.isdeleted(page))
+        self.assertEqual(len(page_about_to_be_removed_spy), 1)
+        self.assertEqual(page_about_to_be_removed_spy[-1][0], 0)
 
         collection.deletePage(page2)
         self.assertEqual(collection.pageCount(), 0)
         self.assertFalse(collection.pages())
         QCoreApplication.sendPostedEvents(None, QEvent.DeferredDelete)
         self.assertTrue(sip.isdeleted(page2))
+        self.assertEqual(len(page_about_to_be_removed_spy), 2)
+        self.assertEqual(page_about_to_be_removed_spy[-1][0], 0)
 
     def testMaxPageWidth(self):
         """