Custom Property On Custom Widget

[Santosh Reddy]

May be I asked a wrong question, we should be looking at Extension class, did you properly implement these

virtual QVariant	property ( int index ) const = 0
virtual QString	propertyGroup ( int index ) const = 0
virtual QString	propertyName ( int index ) const = 0

virtual QVariant	property ( int index ) const = 0
virtual QString	propertyGroup ( int index ) const = 0
virtual QString	propertyName ( int index ) const = 0

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[Ashutosh2k1]

Hi
I have not found very clear explanation of implementation of these function in the documenatation .so can provide me some stuff on this

[Santosh Reddy]

Most of the functions should be clear enough, provided you understand how Qt Designer works. What did you implement in the virtual functions of Extension class?

All these virtual functions should be implemented properly for the widget custom properties to be displayed in Qt Designer.

for example if your widget has 2 QString properties "PRO1", "PRO2" then implementation would like this,

int count() const { return 2; }
 
QVariant property(int index) const
{
    if(index == 0) return pro1;
    else if(index == 1) return pro2;
    else return QVariant;
}
 
QString propertyName(int index) const
{
    if(index == 0) return QString("PRO1");
    else if(index == 1) return QString("PRO2");
    else return QString;
}

int count() const { return 2; }

QVariant property(int index) const
{
    if(index == 0) return pro1;
    else if(index == 1) return pro2;
    else return QVariant;
}

QString propertyName(int index) const
{
    if(index == 0) return QString("PRO1");
    else if(index == 1) return QString("PRO2");
    else return QString;
}

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note you need to implement all the functions properly..

[Ashutosh2k1]

Hi
very very Thanks. I think that now i can implement the Custom (Compound Property ) On the Widget .

[Ashutosh2k1]

Hi,
If I implement my own property sheet extension so in this case i will miss the default property editor given by the widget or the qt designer . But i want to use the both property editor the one provided by the QT designer and other which is written by me So is there any way

[Santosh Reddy]

I not very sure, but this should work, as per documentation

"When implementing a custom widget plugin, a pointer to Qt Designer's current QDesignerFormEditorInterface object is provided by the QDesignerCustomWidgetInterface::initialize() function's parameter."

From the QDesignerFormEditorInterface object, get the previous property editor interface instance, and map the properties in your class, like map 0 to n properties from previous property editor, and n to m are your custom properties, as you know you can get and set the 0 to n properties using previous property editor interface instance

[Ashutosh2k1]

Hi
The Problem is that how can i map those property becoz In the QDesignerPropertyEditorInterface No method is there ,also if i will go for meta object and get the Property through meta object i am not sure it will work .However i am doing work on this
By the way Thanks For Reply Sir

[ViRuSTriNiTy]

If I implement my own property sheet extension so in this case i will miss the default property editor given by the widget or the qt designer . But i want to use the both property editor the one provided by the QT designer and other which is written by me So is there any way

@Ashutosh2k1

I had to solve the same issue. Here is what i came up with after several experiments.

First declare a custom property sheet factory:

class CCustomWidgetPropertySheetFactory : public QExtensionFactory
{
  typedef QExtensionFactory inherited;
 
  public:
    CCustomWidgetPropertySheetFactory(QExtensionManager * apParent);
 
  protected:
    virtual QObject * createExtension(QObject * apObject, const QString & arIId, QObject * apParent) const;
 
  private:
    QExtensionManager * mpExtensionManager;
    mutable bool mCreateExtensionCalled;
};

class CCustomWidgetPropertySheetFactory : public QExtensionFactory
{
  typedef QExtensionFactory inherited;

  public:
    CCustomWidgetPropertySheetFactory(QExtensionManager * apParent);

  protected:
    virtual QObject * createExtension(QObject * apObject, const QString & arIId, QObject * apParent) const;

  private:
    QExtensionManager * mpExtensionManager;
    mutable bool mCreateExtensionCalled;
};

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...then add the implementation of the factory...

CCustomWidgetPropertySheetFactory::CCustomWidgetPropertySheetFactory(QExtensionManager * apParent)
  : inherited(apParent)
  , mpExtensionManager(apParent)
  , mCreateExtensionCalled(false)
{}
 
QObject * CCustomWidgetPropertySheetFactory::createExtension(QObject * apObject, const QString & arIId, QObject /* QExtensionFactory */ * apParent) const
{
  QObject * lResult(0);
 
  if (!mCreateExtensionCalled)
  {
    // note: setting flag to avoid infinite loop caused by later usage of qt_extension<>
    mCreateExtensionCalled = true;
 
    if (arIId == Q_TYPEID(QDesignerPropertySheetExtension))
    {
      CCustomWidget * lCustomWidget(qobject_cast<CCustomWidget *>(apObject));
      if (lCustomWidget)
      {
        QDesignerPropertySheetExtension * lDefaultPropertySheetExtensionImplementor(qt_extension<QDesignerPropertySheetExtension *>(mpExtensionManager, apObject));
        if (lDefaultPropertySheetExtensionImplementor)
        {
          lResult = new CCustomWidgetPropertySheetExtension(apParent, *lDefaultPropertySheetExtensionImplementor);
        }
      }
    }
 
    mCreateExtensionCalled = false;
  }
 
  return lResult;
}

CCustomWidgetPropertySheetFactory::CCustomWidgetPropertySheetFactory(QExtensionManager * apParent)
  : inherited(apParent)
  , mpExtensionManager(apParent)
  , mCreateExtensionCalled(false)
{}

QObject * CCustomWidgetPropertySheetFactory::createExtension(QObject * apObject, const QString & arIId, QObject /* QExtensionFactory */ * apParent) const
{
  QObject * lResult(0);

  if (!mCreateExtensionCalled)
  {
    // note: setting flag to avoid infinite loop caused by later usage of qt_extension<>
    mCreateExtensionCalled = true;

    if (arIId == Q_TYPEID(QDesignerPropertySheetExtension))
    {
      CCustomWidget * lCustomWidget(qobject_cast<CCustomWidget *>(apObject));
      if (lCustomWidget)
      {
        QDesignerPropertySheetExtension * lDefaultPropertySheetExtensionImplementor(qt_extension<QDesignerPropertySheetExtension *>(mpExtensionManager, apObject));
        if (lDefaultPropertySheetExtensionImplementor)
        {
          lResult = new CCustomWidgetPropertySheetExtension(apParent, *lDefaultPropertySheetExtensionImplementor);
        }
      }
    }

    mCreateExtensionCalled = false;
  }

  return lResult;
}

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So far we created a custom property sheet and pass the default property sheet to it. Now declare the custom property sheet (i simplified the code for better understanding here):

class CCustomWidgetPropertySheetExtension : public QObject, public QDesignerPropertySheetExtension
{
  Q_OBJECT
  Q_INTERFACES(QDesignerPropertySheetExtension)
 
  public:
    CCustomWidgetPropertySheetExtension(QObject * apParent,
                                      QDesignerPropertySheetExtension & apDefaultPropertySheetExtension);
    virtual ~CCustomWidgetPropertySheetExtension();
 
    virtual int count() const;
 
    virtual int indexOf(const QString &name) const;
 
    virtual QString propertyName(int index) const;
 
    virtual QString propertyGroup(int index) const;
 
    virtual bool isVisible(int index) const;
 
    virtual QVariant property(int index) const;
 
    ...
 
  private:
    QDesignerPropertySheetExtension & mpDefaultPropertySheetExtension;
    int mPropertyCount;
};

class CCustomWidgetPropertySheetExtension : public QObject, public QDesignerPropertySheetExtension
{
  Q_OBJECT
  Q_INTERFACES(QDesignerPropertySheetExtension)

  public:
    CCustomWidgetPropertySheetExtension(QObject * apParent,
                                      QDesignerPropertySheetExtension & apDefaultPropertySheetExtension);
    virtual ~CCustomWidgetPropertySheetExtension();

    virtual int count() const;

    virtual int indexOf(const QString &name) const;

    virtual QString propertyName(int index) const;

    virtual QString propertyGroup(int index) const;

    virtual bool isVisible(int index) const;

    virtual QVariant property(int index) const;

    ...

  private:
    QDesignerPropertySheetExtension & mpDefaultPropertySheetExtension;
    int mPropertyCount;
};

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...and add the implementation of the custom property sheet...

CCustomWidgetPropertySheetExtension::CCustomWidgetPropertySheetExtension(QObject * apParent,
                                                                     QDesignerPropertySheetExtension & apDefaultPropertySheetExtension)
  : QObject(apParent)
  , QDesignerPropertySheetExtension()
  , mpDefaultPropertySheetExtension(apDefaultPropertySheetExtension)
  , mPropertyCount(mpDefaultPropertySheetExtension.count() + 1)
{}
 
CCustomWidgetPropertySheetExtension::~CCustomWidgetPropertySheetExtension()
{}
 
...
 
int CCustomWidgetPropertySheetExtension::count() const
{
  return mPropertyCount;
}
 
int CCustomWidgetPropertySheetExtension::indexOf( const QString& name ) const
{
  if (name == "MyCustomProperty")
    return mPropertyCount - 1;
  else
    return mpDefaultPropertySheetExtension.indexOf(name);
}
 
QString CCustomWidgetPropertySheetExtension::propertyName( int index ) const
{
  if (index == mPropertyCount - 1)
    return "MyCustomProperty";
  else
    return mpDefaultPropertySheetExtension.propertyName(index);
}
 
QString CCustomWidgetPropertySheetExtension::propertyGroup( int index ) const
{
  if (index == mPropertyCount - 1)
    return "MyCustomPropertyGroup";
  else
    return mpDefaultPropertySheetExtension.propertyGroup(index);
}
 
bool CCustomWidgetPropertySheetExtension::isVisible( int index ) const
{
  if (index == mPropertyCount - 1)
    return true;
  else
    return mpDefaultPropertySheetExtension.isVisible(index);
}
 
QVariant CCustomWidgetPropertySheetExtension::property( int index ) const
{
  if (index == mPropertyCount - 1)
    return QVariant(true);
  else
    return mpDefaultPropertySheetExtension.property(index);
}

CCustomWidgetPropertySheetExtension::CCustomWidgetPropertySheetExtension(QObject * apParent,
                                                                     QDesignerPropertySheetExtension & apDefaultPropertySheetExtension)
  : QObject(apParent)
  , QDesignerPropertySheetExtension()
  , mpDefaultPropertySheetExtension(apDefaultPropertySheetExtension)
  , mPropertyCount(mpDefaultPropertySheetExtension.count() + 1)
{}

CCustomWidgetPropertySheetExtension::~CCustomWidgetPropertySheetExtension()
{}

...

int CCustomWidgetPropertySheetExtension::count() const
{
  return mPropertyCount;
}

int CCustomWidgetPropertySheetExtension::indexOf( const QString& name ) const
{
  if (name == "MyCustomProperty")
    return mPropertyCount - 1;
  else
    return mpDefaultPropertySheetExtension.indexOf(name);
}

QString CCustomWidgetPropertySheetExtension::propertyName( int index ) const
{
  if (index == mPropertyCount - 1)
    return "MyCustomProperty";
  else
    return mpDefaultPropertySheetExtension.propertyName(index);
}

QString CCustomWidgetPropertySheetExtension::propertyGroup( int index ) const
{
  if (index == mPropertyCount - 1)
    return "MyCustomPropertyGroup";
  else
    return mpDefaultPropertySheetExtension.propertyGroup(index);
}

bool CCustomWidgetPropertySheetExtension::isVisible( int index ) const
{
  if (index == mPropertyCount - 1)
    return true;
  else
    return mpDefaultPropertySheetExtension.isVisible(index);
}

QVariant CCustomWidgetPropertySheetExtension::property( int index ) const
{
  if (index == mPropertyCount - 1)
    return QVariant(true);
  else
    return mpDefaultPropertySheetExtension.property(index);
}

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Compile and you will see the custom property "MyCustomProperty" displayed in the designer in the property group "MyCustomPropertyGroup" for the widget "CCustomWidget".

Hope this helps.

So lonG
Daniel

[Olumide]

Hello Daniel, thanks for your post. I've tried to follow your example. Unfortunately the cast

QDesignerPropertySheetExtension* defaultPropertySheetExtension = qt_extension<QDesignerPropertySheetExtension*>( m_extensionManager , object );

QDesignerPropertySheetExtension* defaultPropertySheetExtension = qt_extension<QDesignerPropertySheetExtension*>( m_extensionManager , object );

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makes Qt Designer crash.

[ViRuSTriNiTy]

...makes Qt Designer crash.

What kind of crash exactly? Do you get a stack strace, exception message or anything like that?

[Olumide]

What kind of crash exactly? Do you get a stack strace, exception message or anything like that?

I've just found the cause of the problem. I did not guard against recursive calls to createExtension(). I've just done so however and I no longer get crashes, although I used a static variable like so

QObject* CustomWidgetFactory::createExtension(QObject *object, const QString &iid, QObject* parent ) const
{
	static bool extensionSheetIsInitialized = false;
 
	if( !extensionSheetIsInitialized )
	{
		extensionSheetIsInitialized = true;
		...
	}
 
	return 0;
}

QObject* CustomWidgetFactory::createExtension(QObject *object, const QString &iid, QObject* parent ) const
{
	static bool extensionSheetIsInitialized = false;

	if( !extensionSheetIsInitialized )
	{
		extensionSheetIsInitialized = true;
		...
	}

	return 0;
}

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There is now the larger issue of how to proceed. How do I assign my indexes to my widget properties? So that I can control whether they are shown in the the properties editor? Ideally what I'd like to do is to display a subset of relevant properties of the widget depending on the value of a master property. For example, the master property could represent the shape of the wigdet while the remaining properties could include radius (for circles), length for squared etc, where the radius property is displayed only of the mater property is set to circle.

[ViRuSTriNiTy]

I've just found the cause of the problem. I did not guard against recursive calls to createExtension()

Yep, thats why i added the red comment to mCreateExtensionCalled, back then i stumble upon this recursion too.

How do I assign my indexes to my widget properties? So that I can control whether they are shown in the the properties editor? Ideally what I'd like to do is to display a subset of relevant properties of the widget depending on the value of a master property. For example, the master property could represent the shape of the wigdet while the remaining properties could include radius (for circles), length for squared etc, where the radius property is displayed only of the mater property is set to circle.

The only solution i had found was to use a "index"-"property name" map. With that in mind i would suggest you

1) enumerate all properties of your widget in the constructor of the property sheet class
2) remember those properties in the "index"-"property name" map
3) override each virtual function of the property sheet and return the appropriate property values by using the "index"-"property name" map

I'm sorry that i cannot post any additional code because it's lost. But i closely remember what i was doing back then.