C++ 外观模式讲解和代码示例

/** * The Subsystem can accept requests either from the facade or client directly. * In any case, to the Subsystem, the Facade is yet another client, and it's not * a part of the Subsystem. */ class Subsystem1 { public: std::string Operation1() const { return "Subsystem1: Ready!\n"; } // ... std::string OperationN() const { return "Subsystem1: Go!\n"; } }; /** * Some facades can work with multiple subsystems at the same time. */ class Subsystem2 { public: std::string Operation1() const { return "Subsystem2: Get ready!\n"; } // ... std::string OperationZ() const { return "Subsystem2: Fire!\n"; } }; /** * The Facade class provides a simple interface to the complex logic of one or * several subsystems. The Facade delegates the client requests to the * appropriate objects within the subsystem. The Facade is also responsible for * managing their lifecycle. All of this shields the client from the undesired * complexity of the subsystem. */ class Facade { protected: Subsystem1 *subsystem1_; Subsystem2 *subsystem2_; /** * Depending on your application's needs, you can provide the Facade with * existing subsystem objects or force the Facade to create them on its own. */ public: /** * In this case we will delegate the memory ownership to Facade Class */ Facade( Subsystem1 *subsystem1 = nullptr, Subsystem2 *subsystem2 = nullptr) { this->subsystem1_ = subsystem1 ?: new Subsystem1; this->subsystem2_ = subsystem2 ?: new Subsystem2; } ~Facade() { delete subsystem1_; delete subsystem2_; } /** * The Facade's methods are convenient shortcuts to the sophisticated * functionality of the subsystems. However, clients get only to a fraction of * a subsystem's capabilities. */ std::string Operation() { std::string result = "Facade initializes subsystems:\n"; result += this->subsystem1_->Operation1(); result += this->subsystem2_->Operation1(); result += "Facade orders subsystems to perform the action:\n"; result += this->subsystem1_->OperationN(); result += this->subsystem2_->OperationZ(); return result; } }; /** * The client code works with complex subsystems through a simple interface * provided by the Facade. When a facade manages the lifecycle of the subsystem, * the client might not even know about the existence of the subsystem. This * approach lets you keep the complexity under control. */ void ClientCode(Facade *facade) { // ... std::cout << facade->Operation(); // ... } /** * The client code may have some of the subsystem's objects already created. In * this case, it might be worthwhile to initialize the Facade with these objects * instead of letting the Facade create new instances. */ int main() { Subsystem1 *subsystem1 = new Subsystem1; Subsystem2 *subsystem2 = new Subsystem2; Facade *facade = new Facade(subsystem1, subsystem2); ClientCode(facade); delete facade; return 0; } 

Facade initializes subsystems: Subsystem1: Ready! Subsystem2: Get ready! Facade orders subsystems to perform the action: Subsystem1: Go! Subsystem2: Fire!