命令模式
定义
将请求封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象。命令模式支持可撤销操作。
类图
代码示例
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| class Light {
public:
void on() {
cout << "Light on!" << endl;
}
void off() {
cout << "light off!" << endl;
}
};
class Door {
public:
void open() {
cout << "Door open!" << endl;
}
void close() {
cout << "Door close!" << endl;
}
};
class Command {
public:
virtual void execute() = 0;
virtual void undo() = 0;
};
class LightOnCommand :public Command {
public:
LightOnCommand(Light* li) :light(li) {
}
void execute() {
light->on();
}
void undo() {
light->off();
}
private:
Light* light;
};
class LightOffCommand :public Command {
public:
LightOffCommand(Light* li) :light(li) {
}
void execute() {
light->off();
}
void undo() {
light->on();
}
private:
Light* light;
};
class DoorOpenCommand :public Command {
public:
DoorOpenCommand(Door* doo) :door(doo) {
}
void execute() {
door->open();
}
void undo() {
door->close();
}
private:
Door* door;
};
class DoorCloseCommand :public Command {
public:
DoorCloseCommand(Door* doo) :door(doo) {
}
void execute() {
door->close();
}
void undo() {
door->open();
}
private:
Door* door;
};
class RemoteControl {
private:
Command* onCommand;
Command* offCommand;
public:
RemoteControl() :onCommand(nullptr), offCommand(nullptr) {
}
void setCommand(Command* onCommand, Command* offCommand) {
this->offCommand = offCommand;
this->onCommand = onCommand;
}
void onButtonPushed() {
if (onCommand) {
onCommand->execute();
}
}
void offButtonPushed() {
if (offCommand) {
offCommand->execute();
}
}
};
|
理解
利用command接口，每个动作都继承这个接口成为一个命令对象，命令对象持有一个执行命令的实体，当该动作执行时，命令对象直接调用执行者的对应动作。有利于动作扩展，新动作只要继承command接口就行。