我经常需要实现一个对象，它能够根据用户命令切换其行为。例如，这可能是表示连接到PC并通过GUI由用户控制的设备的类的情况。更一般地说，设备必须独立运行，具有自己的操作调度。
由于我想要从特定设备类中“提取”此行为以增强代码重用性，因此在这里我提出了使用Qt的模板化有限状态机类。我还在A类中报告了一个示例用法。你们（比我更有经验的程序员）认为呢？这是设计这样一个类的“正确”方式吗？是否存在性能问题？
template < class Base,
typename T,
class ThreadPolicy>
class FSM
{
public:
typedef bool (Base::*my_func)();
struct SState {
SState(){}
SState(const T& id_arg,
const T& next_arg,
const T& error_arg,
const QList<T>& branches_arg,
const my_func& op_arg) :
id(id_arg),
next(next_arg),
error(error_arg),
branches(branches_arg),
op(op_arg)
{}
T id; // state ID
T next; // next state
T error; // in case of error
QList<T> branches; // allowed state switching from current
my_func op; // operation associated with current state
};
typedef QMap<T ,SState> SMap;
bool switchState(const T& ns){
return _checkAllowed(ns);
}
bool addState(const T& id, const SState& s){
return _register(id, s);
}
protected:
void _loop(Base* ptr){
if ((ptr->*m_states[m_state].op)()) {
ThreadPolicy::Lock();
if(m_externalSwitch){
m_externalSwitch = false;
ThreadPolicy::Unlock();
return;
}
m_state = m_states[m_state].next;
ThreadPolicy::Unlock();
} else {
ThreadPolicy::Lock();
if(m_externalSwitch){
m_externalSwitch = false;
ThreadPolicy::Unlock();
return;
}
m_state = m_states[m_state].error;
ThreadPolicy::Unlock();
}
}
bool _checkAllowed(const T& cmd){
if (!m_states[m_state].branches.contains(cmd)) { return false;}
ThreadPolicy::Lock();
m_state = cmd;
m_externalSwitch = true;
ThreadPolicy::Unlock();
return true;
}
bool _register(const SState& s){
if(m_states.find(s.id) != m_states.end()) { return false; } // state with same ID already exist
m_states[s.id] = s; // add the new state to the map
return true;
}
SMap m_states; // map states to Baseclass methods
T m_state; // holds my current state
bool m_externalSwitch; // check if user request a state switch
};
class A :
public QObject,
public FSM< A, QString, MultiThreaded >
{
Q_OBJECT
A(){
// SState startState; myState.branches << "start" << "stop";
_register(SState("start",
"start",
"stop",QStringList(("start","stop")),
&A::_doStart));
_register(SState("stop",
"stop",
"stop",QStringList(("stop","start")),
&A::_doStop));
}
private slots:
void run(){
for(;;){
_loop(this);
QCoreApplication::processEvents();
}
}
private:
bool _doStart(){ return true;}
bool _doStop(){ return true;}
};