Pointers and Q_PROPERTY

[jacek]

can this be done at all?

To some extent:

#include <QtDebug>
 
#include <QCoreApplication>
#include <QObject>
#include <QVariant>
 
class BInterface
{
   public:
      virtual int foo() = 0;
};
 
class B : public QObject, public BInterface
{
   Q_OBJECT
   Q_PROPERTY( int b READ b WRITE setB )
   public:
 
      virtual int foo() { return mv_b; }
 
      const int b() const { return mv_b; }
      void setB( int b ) { mv_b = b; }
 
   private:
      int mv_b;
};
 
class A : public QObject
{
   Q_OBJECT
   Q_PROPERTY( QObject* B READ B WRITE setB )
   public:
      A( QObject *b = 0 ) : mv_B( b ) {}
      virtual ~A() { if(mv_B) delete mv_B; }
     QObject * B() { return mv_B; }
      void setB( QObject* B ) { if (mv_B) delete mv_B; mv_B = B; }
 
   private:
      QObject* mv_B;
};
 
int main( int argc, char **argv )
{
  QCoreApplication app( argc, argv );
 
  QObject *a = new A( new B() );
 
  // QObject *a = new A();
  // a->setProperty( "B", 0 );   // works
 
  // QObject *a = new A();
  // a->setProperty( "B", new B() ); // crashes
 
  QObject* b1 = a->property( "B" ).value< QObject *>();
  if( b1 != 0 ) {
     b1->setProperty( "b", 1234 );
  }
  else {
     qDebug() << "b1 is null";
  }
 
  QObject* b2 = a->property( "B" ).value< QObject *>();
  if( b2 != 0 ) {
     qDebug() << b2->property( "b" );
  }
  else {
     qDebug() << "b2 is null";
  }
 
  return 0;
}
 
#include "main.moc"

#include <QtDebug>

#include <QCoreApplication>
#include <QObject>
#include <QVariant>

class BInterface
{
   public:
      virtual int foo() = 0;
};

class B : public QObject, public BInterface
{
   Q_OBJECT
   Q_PROPERTY( int b READ b WRITE setB )
   public:

      virtual int foo() { return mv_b; }

      const int b() const { return mv_b; }
      void setB( int b ) { mv_b = b; }

   private:
      int mv_b;
};

class A : public QObject
{
   Q_OBJECT
   Q_PROPERTY( QObject* B READ B WRITE setB )
   public:
      A( QObject *b = 0 ) : mv_B( b ) {}
      virtual ~A() { if(mv_B) delete mv_B; }
     QObject * B() { return mv_B; }
      void setB( QObject* B ) { if (mv_B) delete mv_B; mv_B = B; }

   private:
      QObject* mv_B;
};

int main( int argc, char **argv )
{
  QCoreApplication app( argc, argv );

  QObject *a = new A( new B() );

  // QObject *a = new A();
  // a->setProperty( "B", 0 );   // works

  // QObject *a = new A();
  // a->setProperty( "B", new B() ); // crashes

  QObject* b1 = a->property( "B" ).value< QObject *>();
  if( b1 != 0 ) {
     b1->setProperty( "b", 1234 );
  }
  else {
     qDebug() << "b1 is null";
  }

  QObject* b2 = a->property( "B" ).value< QObject *>();
  if( b2 != 0 ) {
     qDebug() << b2->property( "b" );
  }
  else {
     qDebug() << "b2 is null";
  }

  return 0;
}

#include "main.moc"

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Output:

$ ./properties
QVariant(int, 1234)