A simple template class which implements snap-to-edge functionality for some QWidgets.

CSnapDialog.h

#include <QWidget>

const int ENABLE_STICK_VALUE = 50;

template< typename T>
class CSnapDialog
{

public:
	CSnapDialog( T* source ) 
		: m_source( source ){};

	bool SnapToParent()
	{
		Q_ASSERT( m_source && m_source->parent() );

		if ( m_source == nullptr || m_source->parent() == nullptr )
			return false;

		QRect rtParent = dynamic_cast<QWidget*>( m_source->parent())->frameGeometry();
		QRect rtChild = m_source->frameGeometry();

		QRect rtAdjust = rtParent.adjusted( - ENABLE_STICK_VALUE, - ENABLE_STICK_VALUE, ENABLE_STICK_VALUE, ENABLE_STICK_VALUE );
		if( rtAdjust.contains( rtChild.topLeft() ) )
		{
			if ( rtChild.left() > rtParent.right() )
				m_source->move( rtParent.right(), rtParent.top() );
		}
		else if ( rtAdjust.contains( rtChild.topRight() ) )
		{
			if ( rtChild.right() < rtParent.left() )
				m_source->move( rtParent.left() - rtChild.width(), rtParent.top() );
		}

		return true;
	}

private:
	T* m_source;

};