fix crash when using plugin that supplies a QDesignerMemberSheetExtension

plugins external to Qt Designer can not define objects inheriting from QDesignerMemberSheet, as that is defined in a private header.  the functions isQt3Signal and isQt3Slot assume that all QDesignerMemberSheetExtension objects at QDesignerMemberSheet, but this is not the case with 3rd party plugins.

Merge-request: 452
Reviewed-By: Thiago Macieira <thiago.macieira@nokia.com>
Reviewed-By: Thorbjørn Lindeijer

1 files changed, 2 insertions, 2 deletions

diff --git a/tools/designer/src/components/signalsloteditor/signalslot_utils.cpp b/tools/designer/src/components/signalsloteditor/signalslot_utils.cpp
index 37269c556b..c268d5f7d7 100644
--- a/tools/designer/src/components/signalsloteditor/signalslot_utils.cpp
+++ b/tools/designer/src/components/signalsloteditor/signalslot_utils.cpp
@@ -275,7 +275,7 @@ namespace qdesigner_internal {
                     const QDesignerMemberSheet *memberSheet
                             = qobject_cast<QDesignerMemberSheet*>(core->extensionManager()->extension(object,
                                                                                                       Q_TYPEID(QDesignerMemberSheetExtension)));
-                    return memberSheet->isQt3Signal(i);
+                    return (memberSheet && memberSheet->isQt3Signal(i));
                 }
         }
 
@@ -294,7 +294,7 @@ namespace qdesigner_internal {
                     const QDesignerMemberSheet *memberSheet
                             = qobject_cast<QDesignerMemberSheet*>(core->extensionManager()->extension(object,
                                                                                                       Q_TYPEID(QDesignerMemberSheetExtension)));
-                    return memberSheet->isQt3Slot(i);
+                    return (memberSheet && memberSheet->isQt3Slot(i));
                 }
         }
         return false;