wxWidgets/interface/wx/persist.h

/////////////////////////////////////////////////////////////////////////////
// Name:        wx/persist.h
// Purpose:     interface of wxPersistenceManager and related classes
// Author:      Vadim Zeitlin
// RCS-ID:      $Id$
// Copyright:   (c) 2009 Vadim Zeitlin <vadim@wxwidgets.org>
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/**
    Provides support for automatically saving and restoring object properties
    to persistent storage.

    This class is the central element of wxWidgets persistence framework, see
    @ref overview_persistence for its overview.

    This is a singleton class and its unique instance can be retrieved using
    Get() method.

    @library{wxcore}
 */
class wxPersistenceManager
{
public:
    /**
        Returns the unique persistence manager object.
     */
    static wxPersistenceManager& Get();

    /**
        Globally disable saving the persistence object properties.

        By default, saving properties in Save() is enabled but the program may
        wish to disable if, for example, it detects that it is running on a
        system which shouldn't be modified in any way and so configuration
        file (or Windows registry) shouldn't be written to.

        @see DisableRestoring()
     */
    bool DisableSaving();

    /**
        Globally disable restoring the persistence object properties.

        By default, restoring properties in Restore() is enabled but this
        function allows to disable it. This is mostly useful for testing.

        @see DisableSaving()
     */
    bool DisableRestoring();


    /**
        Register an object with the manager automatically creating a
        persistence adapter for it.

        This is equivalent to calling Register(void *, wxPersistentObject *)
        with wxCreatePersistentObject(obj) as the second argument.

        @param obj
            The object to register. wxCreatePersistentObject() overload must be
            defined for the objects of this class.
     */
    template <class T>
    wxPersistentObject *Register(T *obj);

    /**
        Register an object with the manager.

        Note that registering the object doesn't do anything except allowing to
        call Restore() for it later. If you want to register the object and
        restore its properties, use RegisterAndRestore().

        The manager takes ownership of @a po and will delete it when it is
        unregistered.

        @param obj
            The object to register.
        @param po
            The wxPersistentObject to use for saving and restoring this object
            properties.
     */
    wxPersistentObject *Register(void *obj, wxPersistentObject *po);

    /**
        Check if the object is registered and return the associated
        wxPersistentObject if it is or @NULL otherwise.
     */
    wxPersistentObject *Find(void *obj) const;

    /**
        Unregister the object and delete the associated wxPersistentObject.

        For the persistent windows this is done automatically (via
        SaveAndUnregister()) when the window is destroyed so you only need to
        call this function explicitly if you are using custom persistent
        objects or if you want to prevent the object properties from being
        saved.

        @param obj
            An object previously registered with Register().
     */
    void Unregister(void *obj);


    /**
        Save the object properties to persistent storage.

        This method does nothing if DisableSaving() had been called.

        @param obj
            An object previously registered with Register().

        @see SaveAndUnregister()
     */
    void Save(void *obj);

    /**
        Restore the object properties previously saved by Save().

        This method does nothing if DisableRestoring() had been called.

        @param obj
            An object previously registered with Register().
        @return
            @true if the object properties were restored or @false if nothing
            was found to restore or the saved settings were invalid.

        @see RegisterAndRestore()
     */
    bool Restore(void *obj);

    /// Combines both Save() and Unregister() calls.
    void SaveAndUnregister(void *obj);

    /// Combines both Register() and Restore() calls.
    //@{
    template <class T>
    bool RegisterAndRestore(T *obj);

    bool RegisterAndRestore(void *obj, wxPersistentObject *po);
    //@}
};

/**
    Base class for persistent object adapters.

    wxWidgets persistence framework is non-intrusive, i.e. can work with the
    classes which have no relationship to nor knowledge of it. To allow this,
    an intermediate persistence adapter is used: this is just a simple object
    which provides the methods used by wxPersistenceManager to save and restore
    the object properties and implements them using the concrete class methods.

    You may derive your own classes from wxPersistentObject to implement
    persistence support for your common classes, see @ref persistence_defining.

    @see wxPersistentWindow<>
 */
class wxPersistentObject
{
public:
    /**
        Constructor takes the object which we're associated with.

        This object must have life-time greater than ours as we keep a pointer
        to it.
     */
    wxPersistentObject(void *obj);

    /// Trivial but virtual destructor.
    virtual ~wxPersistentObject();


    /**
        @name Methods to be implemented in the derived classes.

        Notice that these methods are only used by wxPersistenceManager
        normally and shouldn't be called directly.
     */
    //@{

    /**
        Save the object properties.

        The implementation of this method should use SaveValue().
     */
    virtual void Save() const = 0;

    /**
        Restore the object properties.

        The implementation of this method should use RestoreValue().
     */
    virtual bool Restore() = 0;


    /**
        Returns the string uniquely identifying the objects supported by this
        adapter.

        This method is called from SaveValue() and RestoreValue() and normally
        returns some short (but not too cryptic) strings, e.g. @c "Checkbox".
     */
    virtual wxString GetKind() const = 0;

    /**
        Returns the string uniquely identifying the object we're associated
        with among all the other objects of the same type.

        This method is used together with GetKind() to construct the unique
        full name of the object in e.g. a configuration file.
     */
    virtual wxString GetName() const = 0;

    //@}


    /// Return the associated object.
    void *GetObject() const;

protected:
    /**
        Save the specified value using the given name.

        @param name
            The name of the value in the configuration file.
        @param value
            The value to save, currently must be a type supported by wxConfig.
        @return
            @true if the value was saved or @false if an error occurred.
     */
    template <typename T>
    bool SaveValue(const wxString& name, T value) const;

    /**
        Restore the value saved by Save().

        @param name
            The same name as was used by Save().
        @param value
            Non-@NULL pointer which will be filled with the value if it was
            read successfully or not modified if it wasn't.
        @return
            @true if the value was successfully read or @false if it was not
            found or an error occurred.
     */
    template <typename T>
    bool RestoreValue(const wxString& name, T *value);
};

/**
    Function used to create the correct persistent adapter for the given type
    of objects.

    To be precise, there is no such template function definition but there are
    overloads of wxCreatePersistentObject() taking different object types for
    all wxWidgets classes supporting persistence. And you may also define your
    own overloads to integrate your custom classes with wxWidgets persistence
    framework.

    @see @ref persistence_defining

    @header{wx/persist.h}
 */
template <class T>
wxPersistentObject *wxCreatePersistentObject(T *obj);

/**
    A shorter synonym for wxPersistenceManager::RegisterAndRestore().

    This function simply calls wxPersistenceManager::RegisterAndRestore() but
    using it results in slightly shorter code as it calls
    wxPersistenceManager::Get() internally.

    For the implementation reasons, this function @em mucst be used instead of
    the template method when using Microsoft Visual C++ 6 compiler.

    @header{wx/persist.h}
 */
template <class T>
bool wxPersistentRegisterAndRestore(T *obj);