Fix #10703 (selection reset after added/removed attribute)

Author: wonder-sk

src/gui/qgsfieldmodel.cpp

@@ -86,8 +86,59 @@ void QgsFieldModel::updateModel()
 {
   if ( mLayer )
   {
-    if ( mFields.toList() != mLayer->pendingFields().toList() )
+    QgsFields newFields = mLayer->pendingFields();
+    if ( mFields.toList() != newFields.toList() )
     {
+      // Try to handle two special cases: addition of a new field and removal of a field.
+      // It would be better to listen directly to attributeAdded/attributeDeleted
+      // so we would not have to check for addition/removal here.
+
+      if ( mFields.count() == newFields.count() - 1 )
+      {
+        QgsFields tmpNewFields = newFields;
+        tmpNewFields.remove( tmpNewFields.count() - 1 );
+        if ( mFields.toList() == tmpNewFields.toList() )
+        {
+          // the only change is a new field at the end
+          beginInsertRows( QModelIndex(), mFields.count(), mFields.count() );
+          mFields = newFields;
+          endInsertRows();
+          return;
+        }
+      }
+
+      if ( mFields.count() == newFields.count() + 1 )
+      {
+        QgsFields tmpOldFields = mFields;
+        tmpOldFields.remove( tmpOldFields.count() - 1 );
+        if ( tmpOldFields.toList() == newFields.toList() )
+        {
+          // the only change is a field removed at the end
+          beginRemoveRows( QModelIndex(), mFields.count() - 1, mFields.count() - 1 );
+          mFields = newFields;
+          endRemoveRows();
+          return;
+        }
+
+        for ( int i = 0; i < newFields.count(); ++i )
+        {
+          if ( mFields.at( i ) != newFields.at( i ) )
+          {
+            QgsFields tmpOldFields = mFields;
+            tmpOldFields.remove( i );
+            if ( tmpOldFields.toList() != newFields.toList() )
+              break; // the change is more complex - go with general case
+
+            // the only change is a field removed at index i
+            beginRemoveRows( QModelIndex(), i, i );
+            mFields = newFields;
+            endRemoveRows();
+            return;
+          }
+        }
+      }
+
+      // general case with reset - not good - resets selections
       beginResetModel();
       mFields = mLayer->pendingFields();
       endResetModel();