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I'm developing a Symbian application. I've written a system for easily changing views, roughly like this:

class ViewManager : public QWidget {
   public slots:
      void changeView( const QString &id ) {
         if( currentView_m ) {
            delete currentView_m;
            currentView_m = 0;
         }

         if( id == "main" ) {
            currentView = new MainView( this );
         }
         else if( ... ) {
            //etc..

         layout_m->addWidget( currentView_m );
         connect( currentView_m, SIGNAL( changeView( QString ) ),
                  this, SLOT( changeView( QString ) ) );
      }
   private:
      View *currentView_m;
};

class View : public QWidget {
   signals:
      void ChangeView( const QString &id );
};

class MainView : public View {
   public slots:
      void onButtonClicked() {
         emit changeView( "someview" );
      } 
};

Then as an example, I'm using the ViewManager in main:

int main( int argc, char *argv[] ) {
   QApp app...

   ViewManager man;
   man.changeView( "main" );

   app.exec();
}

When I change the view the first time, it works just fine, then when I change the view another time, it segfaults! You might think it segfaults when I delete the currentView_m pointer, but no! The segmentation fault happens right after the program exits the changeView-slot.

I have no idea how to debug this, as the program crashes and shows a disassembler dump, and the stack trace shows only gibberish.

Could it be that after the slot call, the program goes to the QApplication event loop and crashes there? I'm using a custom widgets inside View implementations that override some of the protected QWidget events.

Gerstmann
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2 Answers2

1

You are deleting a object the signal of which you are processing. Instead of delete, just call deleteLater() on the object, deferring the deletion to a "safe" point.

laalto
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  • calling deleteLater() instead of delete solved the crash, but I now have trouble setting focus for the currentView_m, I have to press the widget/view first. calling setFocus() didn't solve the problem. Any Ideas for that? – Gerstmann May 13 '11 at 11:23
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Try removing the view from your layout first. Then delete the view. You can use removeWidget,removeItem methods of layout for this purpose

Layout might be trying to access a delete view.

Read this Qt - remove all widgets from layout? question as well. It might give you insight.

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