llevent.h

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#ifndef LL_EVENT_H
#define LL_EVENT_H

#include "llsd.h"
#include "llmemory.h"
#include "llthread.h"

class LLEventListener;
class LLEvent;
class LLEventDispatcher;
class LLObservable;

// Abstract event. All events derive from LLEvent
class LLEvent : public LLThreadSafeRefCount
{
protected:
        virtual ~LLEvent();
        
public:
        LLEvent(LLObservable* source, const std::string& desc = "") : mSource(source), mDesc(desc) { }

        LLObservable* getSource() { return mSource; }
        virtual LLSD            getValue() { return LLSD(); }
        // Determines whether this particular listener
        //   should be notified of this event.
        // If this function returns true, handleEvent is
        //   called on the listener with this event as the
        //   argument.
        // Defaults to handling all events. Override this
        //   if associated with an Observable with many different listeners
        virtual bool accept(LLEventListener* listener);

        // return a string describing the event
        virtual const std::string& desc();

private:
        LLObservable* mSource;
        std::string mDesc;
};

// Abstract listener. All listeners derive from LLEventListener
class LLEventListener : public LLThreadSafeRefCount
{
protected:
        virtual ~LLEventListener();
        
public:

        // Processes the event.
        // TODO: Make the return value less ambiguous?
        virtual bool handleEvent(LLPointer<LLEvent> event, const LLSD& userdata) = 0;

        // Called when an dispatcher starts/stops listening
        virtual bool handleAttach(LLEventDispatcher *dispatcher) = 0;
        virtual bool handleDetach(LLEventDispatcher *dispatcher) = 0;
};

// A listener which tracks references to it and cleans up when it's deallocated
class LLSimpleListener : public LLEventListener
{
public:
        void clearDispatchers();
        virtual bool handleAttach(LLEventDispatcher *dispatcher);
        virtual bool handleDetach(LLEventDispatcher *dispatcher);

protected:
        ~LLSimpleListener();
        std::vector<LLEventDispatcher *> mDispatchers;
};

class LLObservable; // defined below

// A structure which stores a Listener and its metadata
struct LLListenerEntry
{
        LLEventListener* listener;
        LLSD filter;
        LLSD userdata;
};

// Base class for a dispatcher - an object which listens
// to events being fired and relays them to their
// appropriate destinations.
class LLEventDispatcher : public LLThreadSafeRefCount
{
protected:
        virtual ~LLEventDispatcher();
        
public:
        // The default constructor creates a default simple dispatcher implementation.
        // The simple implementation has an array of listeners and fires every event to
        // all of them.
        LLEventDispatcher();
        
        // This dispatcher is being attached to an observable object.
        // If we return false, the attach fails.
        bool engage(LLObservable* observable);

        // This dispatcher is being detached from an observable object.
        void disengage(LLObservable* observable);

        // Adds a listener to this dispatcher, with a given user data
        // that will be passed to the listener when an event is fired.
        // Duplicate pointers are removed on addtion.
        void addListener(LLEventListener *listener, LLSD filter, const LLSD& userdata);

        // Removes a listener from this dispatcher
        void removeListener(LLEventListener *listener);

        // Gets a list of interested listeners
        std::vector<LLListenerEntry> getListeners() const;

        // Handle an event that has just been fired by communicating it
        // to listeners, passing it across a network, etc.
        bool fireEvent(LLPointer<LLEvent> event, LLSD filter);

public:
        class Impl;
private:
        Impl* impl;
};

// Interface for observable data (data that fires events)
// In order for this class to work properly, it needs
// an instance of an LLEventDispatcher to route events to their
// listeners.
class LLObservable
{
public:
        // Initialize with the default Dispatcher
        LLObservable();
        virtual ~LLObservable();

        // Replaces the existing dispatcher pointer to the new one,
        // informing the dispatcher of the change.
        virtual bool setDispatcher(LLPointer<LLEventDispatcher> dispatcher);

        // Returns the current dispatcher pointer.
        virtual LLEventDispatcher* getDispatcher();

        void addListener(LLEventListener *listener, LLSD filter = "", const LLSD& userdata = "")
        {
                if (mDispatcher.notNull()) mDispatcher->addListener(listener, filter, userdata);
        }
        void removeListener(LLEventListener *listener)
        {
                if (mDispatcher.notNull()) mDispatcher->removeListener(listener);
        }
        // Notifies the dispatcher of an event being fired.
        void fireEvent(LLPointer<LLEvent> event, LLSD filter = LLSD());

protected:
        LLPointer<LLEventDispatcher> mDispatcher;
};

class LLValueChangedEvent : public LLEvent
{
public:
        LLValueChangedEvent(LLObservable* source, LLSD value) : LLEvent(source, "value_changed"), mValue(value) { }
        LLSD getValue() { return mValue; }
        LLSD mValue;
};

#endif // LL_EVENT_H

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