Game Development Reference
In-Depth Information
The bolded lines show that the
Game
class inherits from
QuitObserver
, now has a destructor,
and overloads the
OnQuit
method. Listing 23-13 shows how the constructor and destructor are
responsible for adding and removing the class as a listener to
QuitOption
.
Listing 23-13.NThe
Game
Class Constructor and Destructor
Game::Game()
: m_attackDragonOption{ CreateOption(PlayerOptions::AttackEnemy) }
, m_attackOrcOption{ CreateOption(PlayerOptions::AttackEnemy) }
, m_moveNorthOption{ CreateOption(PlayerOptions::GoNorth) }
, m_moveEastOption{ CreateOption(PlayerOptions::GoEast) }
, m_moveSouthOption{ CreateOption(PlayerOptions::GoSouth) }
, m_moveWestOption{ CreateOption(PlayerOptions::GoWest) }
, m_openSwordChest{ CreateOption(PlayerOptions::OpenChest) }
, m_quitOption{ CreateOption(PlayerOptions::Quit) }
, m_swordChest{ &m_sword }
{
static_cast<OpenChestOption*>(m_openSwordChest.get())->SetChest(&m_swordChest);
m_enemies.emplace_back(CreateEnemy(EnemyType::Dragon));
static_cast<AttackEnemyOption*>(m_attackDragonOption.get())->SetEnemy(m_enemies[0]);
m_enemies.emplace_back(CreateEnemy(EnemyType::Orc));
static_cast<AttackEnemyOption*>(m_attackOrcOption.get())->SetEnemy(m_enemies[1]);
static_cast<QuitOption*>(m_quitOption.get())->AddObserver(this);
}
Game::~Game()
{
static_cast<QuitOption*>(m_quitOption.get())->RemoveObserver(this);
}
The bolded lines again show the relevant updates to the code. The last update in Listing 23-14
implements the
OnQuit
method.
Listing 23-14. The
Game::OnQuit
Method
void Game::OnQuit()
{
m_playerQuit = true;
}
This is all there is to implementing the observer pattern. This has achieved another decoupling
between the
QuitOption
class and any other classes in the game that need to know about quit
events. The observer class is especially useful when creating game framework code for systems
such as online features. You can imagine a situation where you implement a class to download
leaderboards from a web server. This class could be used in multiple game projects and each
individual game could simply implement its own class to observe the downloader and act
appropriately when the leaderboard data has been received.
