设计模式之命令模式(c++)

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命令模式的作用是将函数转换为对象，将实际的操作与并行的框架分离，命令模式属于行为级

类图如下：

代码来源于c++编程思想

class Task {public:    virtual void operation() = 0;};class TaskRunner {              //singleton pattern    static vector<Task*> tasks;    TaskRunner() {}    TaskRunner& operator=(TaskRunner&);    TaskRunner(const TaskRunner&);    static TaskRunner tr;public:    static void add(Task& t) { tasks.push_back(&t); }    static void run() {        vector<Task*>::iterator it = tasks.begin();        while (it != tasks.end())            (*it++)->operation();    }};TaskRunner TaskRunner::tr;      //init static member (non-int)vector<Task*> TaskRunner::tasks;class EventSimulator {    clock_t creation;    clock_t delay;public:    EventSimulator() : creation(clock()) {        delay = CLOCKS_PER_SEC/4 * (rand()%20 + 1);        cout << "delay = " << delay << endl;    }    bool fired() {        return clock() > creation + delay;    }};class Button {    bool pressed;    string id;    EventSimulator e;public:    Button(string name) : id(name), pressed(false) {}    void press() { pressed = true; }    bool isPressed() {        if (e.fired()) press();        return pressed;    }    friend ostream&    operator<<(ostream& os, const Button& b) {        return os << b.id;    }};class CheckButton : public Task {    bool handled;    Button button;public:    CheckButton(Button& b) : button(b), handled(false) {}    void operation() {        if (!handled && button.isPressed()) {            cout << button << "pressed" << endl;            handled = true;        }    }};void procedure() {    TaskRunner::run();}void CommandPatternTest(){    srand(time(0));    Button b1("B1"), b2("B2"), b3("B3");    CheckButton cb1(b1), cb2(b2), cb3(b3);    TaskRunner::add(cb1);    TaskRunner::add(cb2);    TaskRunner::add(cb3);    while (true)    {        procedure();    }}

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