#include <DisplayFactory>
class CDisplayFactory
{
public:
CDisplay* create(const std::string& type);
CDisplayCreator* getCreator(const std::string& type);
bool addCreator(const std::string& type, CDisplayCreator& rCreator);
CDisplayCreator* removeCreator(const std::string& type);
};
The CDisplayFactory class is resonsible
for associating CDisplayCreator objects
with strings (display types). Upon being presented with a
string CDisplayCreator::create searches
its inventory of creators for a match and then delegates the
creation of a displayer to the matching creator object.
Methods are also provided to maintain the contents of the cretor inventory.
Key to the opertion of CDisplayFactory
is a hierarchy of display creator classes. Instances of
these classes are registered with the factory and associated with
an arbitrary display type string.
The base class of these creators, CDisplayCreator
is defined below.
Concrete classes need only implement the
create method to return a pointer to
a new instance of the display type they create. By
convention these are dynamically allocated instances and
must be destroyed by the factory client when no longer needed.
Each distince call to create
should produce a new, unique CDisplay
object
The CDisplayFactory class
implements the following methods:
CDisplay* create(const std::string& type = );
Locates the creator that matches the type
string and requests that it return a pointer to the
corresponding displayer object. In general the
pointer returned is to a dynamically created object
that must be deleted when the client no longer
needs it.
If there is no matching creator, or if the creation fails, nullptr is returned.
CDisplayCreator* getCreator(const std::string& type = );
Returns a pointer ot the creator that
corresponds to the type
string. If there is no matching
creator a nullptr is returned.
bool addCreator(const std::string& type = , CDisplayCreator& rCreator = );
Adds a new creator, rCreator
to the factory and associates it with the type
string type. In general the
creator object is dynamically allocated, however,
there's no actual requirement that it be.
On successful addition, the method returns
true if there is already
a creator with the same type
name, false is returned instead.
CDisplayCreator* removeCreator(const std::string& type = );
Removes the creator object associated with the
type string. The return
value is a pointer to the object, which is no longer
in the inventory of creators known by the factory.
If there is no matching creator,
nullptr is returned instead.