/*+
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* Copyright (c) 2006 Nokia Corporation and/or its subsidiary(-ies).+
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* All rights reserved.+
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* This component and the accompanying materials are made available+
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* under the terms of "Eclipse Public License v1.0"+
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* which accompanies this distribution, and is available+
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* at the URL "http://www.eclipse.org/legal/epl-v10.html".+
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*+
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* Initial Contributors:+
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* Nokia Corporation - initial contribution.+
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*+
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* Contributors:+
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*+
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* Description:   Contains MCatalogsBase interface+
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*+
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*/+
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+
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+
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#ifndef M_CATALOGS_BASE_H+
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#define M_CATALOGS_BASE_H+
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+
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#include <e32cmn.h>+
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#include "catalogsinterfaceids.h"+
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+
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/**+
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 *  This interface provides functions for querying the interfaces that+
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 *  a class implements. Also, functions for reference counter are provided.+
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 *  The reference counter is used to keep track of the number of users+
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 *  of the implemented class. +
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 *+
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 *  +
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 */+
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class MCatalogsBase+
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    {+
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    +
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public:+
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 +
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    /**+
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     * KInterfaceUid defines the identifier for this interface.+
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     * Child interfaces should define their own unique values for their+
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     * KInterfaceUid.+
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     *+
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     * +
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     */+
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    enum { KInterfaceUid = ECatalogsBaseUid };+
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+
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+
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    /**+
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     * This function is used to test if this object contains an implementation of+
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     * the interface of the given type.+
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     *+
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     * If the object contains the interface, a pointer to it is returned, and+
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     * the reference count is increased by one. Otherwise, NULL is returned.+
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     *+
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     * @note This interface does not allow the user to delete object directly +
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     * (destructor is protected). The destruction of this object should be done +
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     * by calling Release-function.+
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     *+
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     * A template shorthand version is provided here, making the usage easier.+
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     * An example of using the template method:+
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     * MWantedInterface* object = +
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     *      someObjectInheritedFromMCatalogBase->QueryInterfaceL< MWantedInterface >();+
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     *+
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     * +
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     * @return Pointer to the object's interface, if the object implements the given+
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     *  interface, NULL otherwise. Counted, Release() must be called after use.+
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     * @see MCatalogsBase::QueryInterfaceLC+
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     */+
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    template< class T >+
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    inline T* QueryInterfaceL()+
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        {+
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        const MCatalogsBase* self = this;+
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        const TAny* interface = self->QueryInterfaceL( T::KInterfaceUid );+
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        return const_cast< T* >( static_cast< const T* >( interface ) );+
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        }+
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    +
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    /**+
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     * This is const version of QueryInterfaceL.+
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     * +
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     */+
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    template< class T >+
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    inline const T* QueryInterfaceL() const+
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        {      +
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        return static_cast< const T* >( QueryInterfaceL( T::KInterfaceUid ) );+
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        }+
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+
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    /**+
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     * Like QueryInterfaceL, tries to retrieve an interface of specified type+
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     * from the object. If the interface pointer is returned, it is appended+
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     * to the cleanup stack, so that a following CleanupStack::PopAndDestroy()+
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     * will call Release() on the interface pointer appropriately.+
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     *+
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     * @return Pointer to the object's interface, if the object implements+
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     * the given interface, or NULL if this object does not implement the+
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     * given interface. If NULL is returned then the object is not pushed to+
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     * the cleanupstack. +
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     *+
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     * +
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     * @return Pointer to the object's interface, if the object implements the given+
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     *  interface, NULL otherwise. Returned non-NULL pointer reference is counted, must+
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     *  be released with a call to CleanupStack::PopAndDestroy().+
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     * @see MCatalogsBase::QueryInterfaceL+
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     */ +
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    template< class T >+
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    inline T* QueryInterfaceLC()+
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        {+
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        T* interface( QueryInterfaceL< T >() );+
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        if ( interface )+
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            {+
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            // Do not push NULL object into the cleanup stack.+
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            CleanupReleasePushL( *interface );        +
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            }+
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        return interface;+
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        }+
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+
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    /**+
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     * This is const version of QueryInterfaceLC.+
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     * +
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     */+
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    template< class T >+
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    inline const T* QueryInterfaceLC() const+
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        {+
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        const T* interface( QueryInterfaceL< const T >() );+
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        if ( interface )+
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            {+
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            // Do not push NULL object into the cleanup stack.+
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            CleanupReleasePushL( *const_cast<T*>( interface ) );        +
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            }+
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        return interface;+
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        }+
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    +
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    /**+
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     * Increments the reference counter.+
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     *+
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     * @note QueryInterfaceL() already increases the value by one+
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     *  if interface check was successfull. This function may be used+
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     *  if user knows that the interface is used in multiple places and+
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     *  Release() is called accordingly.+
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     *+
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     * +
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     * @return New reference count value. For debug purposes only.+
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     */+
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    virtual TInt AddRef() const = 0;		+
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    +
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    /**+
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     * Releases a reference. Deletes the object if the reference count+
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     * reaches 0. +
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     * Notice that destructor is defined as protected. So, the object of+
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     * this interface can be deleted using this function and only after +
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     * reference count is zero.+
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     *+
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     * +
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     * @return Reference count after release. For debug purposes only.+
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     */+
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    virtual TInt Release() const = 0;+
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    +
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    +
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protected:+
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+
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    /**+
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     * QueryInterfaceL+
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     *+
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     * This function is used to test if this object contains an implementation of+
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     * the interface of the given type.+
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     * If the object contains the interface, then the reference count is increased+
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     * by one.+
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     *+
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     * +
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     * @param aInterfaceType TInt that specifies the interface that this object should implement.+
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     * @return Pointer to this object if the object implements given interface +
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     * or NULL if this object does not implement the given interface. Counted, Release() must+
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     * be called after use.+
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     */+
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    virtual const TAny* QueryInterfaceL( TInt aInterfaceType ) const = 0;+
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    +
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+
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    /**+
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     * The destructor of an interface is set virtual to make sure that+
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     * the destructors of derived classes are called appropriately when the+
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     * object is destroyed.+
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     *+
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     * Destructors for MCatalogsBase and all derived interfaces are defined as+
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     * protected to prevent direct use of delete on interface pointers (Release()+
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     * must be called instead of delete).+
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     *+
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     * +
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     */+
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    virtual ~MCatalogsBase() {}+
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+
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    };+
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+
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#endif // M_CATALOGS_BASE_H+
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