lazydelete.hxx

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#ifndef INCLUDED_VCL_LAZYDELETE_HXX
#define INCLUDED_VCL_LAZYDELETE_HXX

#include <vcl/dllapi.h>

#include <com/sun/star/lang/XComponent.hpp>

#include <optional>

namespace vcl
{
    /*
    You may not access vcl objects after DeInitVCL has been called this includes their destruction
    therefore disallowing the existence of static vcl object like e.g. a static BitmapEx
    To work around this use DeleteOnDeinit<BitmapEx> which will allow you to have a static object container,
    that will have its contents destroyed on DeinitVCL. The single drawback is that you need to check on the
    container object whether it still contains content before actually accessing it.

    caveat: when constructing a vcl object, you certainly want to ensure that InitVCL has run already.
    However this is not necessarily the case when using a class static member or a file level static variable.
    In these cases make judicious use of the set() method of DeleteOnDeinit, but beware of the changing
    ownership.

    example use case: use a lazy initialized on call BitmapEx in a paint method. Of course a paint method
    would not normally be called after DeInitVCL anyway, so the check might not be necessary in a
    Window::Paint implementation, but always checking is a good idea.

    SomeWindow::Paint()
    {
        static vcl::DeleteOnDeinit< BitmapEx > aBmp( new BitmapEx( ... ) );

        if( aBmp.get() ) // check whether DeInitVCL has been called already
            DrawBitmapEx( Point( 10, 10 ), *aBmp );
    }
    */

    class VCL_DLLPUBLIC DeleteOnDeinitBase
    {
    public:
        static void SAL_DLLPRIVATE ImplDeleteOnDeInit();
        virtual ~DeleteOnDeinitBase();
    protected:
        static void addDeinitContainer( DeleteOnDeinitBase* i_pContainer );

        virtual void doCleanup() = 0;
    };

    enum class DeleteOnDeinitFlag { Empty };

    template < typename T >
    class DeleteOnDeinit final : public DeleteOnDeinitBase
    {
        std::optional<T> m_pT;
        virtual void doCleanup() override { m_pT.reset(); }
    public:
        template <class... Args >
        DeleteOnDeinit(Args&&... args )
        {
            m_pT.emplace(args...);
            addDeinitContainer( this );
        }
        DeleteOnDeinit(DeleteOnDeinitFlag)
        {
            addDeinitContainer( this );
        }

        // get contents
        T* get() { return m_pT ? &*m_pT : nullptr; }

        // set contents, returning old contents
        // ownership is transferred !
        template <class... Args >
        std::optional<T> set(Args&&... args)
        {
            auto pOld = std::move(m_pT);
            m_pT.emplace(args...);
            return pOld;
        }
    };

    template <typename I>
    class DeleteUnoReferenceOnDeinit final : public vcl::DeleteOnDeinitBase
    {
        css::uno::Reference<I> m_xI;
        virtual void doCleanup() override { set(nullptr); }
    public:
        DeleteUnoReferenceOnDeinit(const css::uno::Reference<I>& r_xI ) : m_xI( r_xI ) {
            addDeinitContainer( this ); }

        css::uno::Reference<I> get() { return m_xI; }

        void set (const css::uno::Reference<I>& r_xNew )
        {
            css::uno::Reference< css::lang::XComponent> xComponent (m_xI, css::uno::UNO_QUERY);
            m_xI = r_xNew;
            if (xComponent.is()) try
            {
                xComponent->dispose();
            }
            catch( css::uno::Exception& )
            {
            }
        }
    };
}

#endif
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