下面是一个fsm的例子，代码如下：

 

1 -module(code_lock2). 2  3 -behaviour(gen_fsm). 4 -export([start_link/1]). 5 -export([button/1]). 6 -export([init/1, locked/2, open/2]). 7 -export([code_change/4, handle_event/3, handle_info/3, handle_sync_event/4, terminate/3]). 8  9 -spec(start_link(Code::string()) -> {ok,pid()} | ignore | {error,term()}).10 start_link(Code) ->11     gen_fsm:start_link({local, code_lock2}, code_lock2, Code, []).12 13 -spec(button(Digit::string()) -> ok).14 button(Digit) ->15     gen_fsm:send_event(code_lock2, {button, Digit}).16 17 init(LockCode) ->18     io:format("init: ~p~n", [LockCode]),19     {ok, locked, {[], LockCode}}.20 21 locked({button, Digit}, {SoFar, Code}) ->22     io:format("buttion: ~p, So far: ~p, Code: ~p~n", [Digit, [SoFar|Digit], Code]),23     InputDigits = lists:append(SoFar, Digit),24     io:format("Right now the password is ~p~n", [InputDigits]),25     case InputDigits of26         Code ->27             do_unlock(),28             {next_state, open, {[], Code}, 10000};29         Incomplete when length(Incomplete)
     
      30             {next_state, locked, {Incomplete, Code}, 5000};31         Wrong ->32             io:format("wrong passwd: ~p~n", [Wrong]),33             {next_state, locked, {[], Code}}34     end;35 locked(timeout, {_SoFar, Code}) ->36     io:format("timout when waiting button inputting, clean the input, button again plz~n"),37     {next_state, locked, {[], Code}}.38 39 open(timeout, State) ->40     do_lock(),41     {next_state, locked, State}.42 43 code_change(_OldVsn, StateName, Data, _Extra) ->44     {ok, StateName, Data}.45 46 terminate(normal, _StateName, _Data) ->47     ok.48 49 handle_event(Event, StateName, Data) ->50     io:format("handle_event... ~n"),51     unexpected(Event, StateName),52     {next_state, StateName, Data}.53 54 handle_sync_event(Event, From, StateName, Data) ->55     io:format("handle_sync_event, for process: ~p... ~n", [From]),56     unexpected(Event, StateName),57     {next_state, StateName, Data}.58 59 handle_info(Info, StateName, Data) ->60     io:format("handle_info...~n"),61     unexpected(Info, StateName),62     {next_state, StateName, Data}.63 64 %% Unexpected allows to log unexpected messages65 unexpected(Msg, State) ->66     io:format("~p RECEIVED UNKNOWN EVENT: ~p, while FSM process in state: ~p~n",67               [self(), Msg, State]).68 %%69 %% actions70 do_unlock() ->71     io:format("passwd is right, open the DOOR.~n").72 73 do_lock() ->74     io:format("over, close the DOOR.~n").
     

 

开锁过程如下：

1 3> code_lock2:button([1]). 2 buttion: [1], So far: [], Code: [1,3,5,3,1,7] 3 Right now the password is [1] 4 ok 5 4> code_lock2:button([3]). 6 buttion: [3], So far: [1], Code: [1,3,5,3,1,7] 7 Right now the password is [1,3] 8 ok 9 5> code_lock2:button([5]).10 buttion: [5], So far: [1,3], Code: [1,3,5,3,1,7]11 Right now the password is [1,3,5]12 ok13 timout when waiting button inputting, clean the input, button again plz14 6> code_lock2:button([3]).15 buttion: [3], So far: [], Code: [1,3,5,3,1,7]16 Right now the password is [3]17 ok18 timout when waiting button inputting, clean the input, button again plz19 7> code_lock2:button([1]).20 buttion: [1], So far: [], Code: [1,3,5,3,1,7]21 Right now the password is [1]22 ok23 8> code_lock2:button([3]).24 buttion: [3], So far: [[1],3], Code: [1,3,5,3,1,7]25 Right now the password is [1,3]26 ok27 9> code_lock2:button([5]).28 buttion: [5], So far: [[1,3],5], Code: [1,3,5,3,1,7]29 Right now the password is [1,3,5]30 ok31 10> code_lock2:button([3]).32 buttion: [3], So far: [1,3,5], Code: [1,3,5,3,1,7]33 Right now the password is [1,3,5,3]34 ok35 11> code_lock2:button([1]).36 buttion: [1], So far: [1,3,5,3], Code: [1,3,5,3,1,7]37 Right now the password is [1,3,5,3,1]38 ok39 12> code_lock2:button([7]).40 buttion: [7], So far: [1,3,5,3,1], Code: [1,3,5,3,1,7]41 Right now the password is [1,3,5,3,1,7]42 ok43 passwd is right, open the DOOR.44 over, close the DOOR.45 13>

 

有一个地方解释一下，使用fsm:send_event(code_lock2, {button, Digit})相当于发送了一个消息，这个消息怎么处理呢？

如果没有fsm，这样的一个问题几乎没法回答！

 

这个消息先交给fsm，由fsm判断该交给谁去处理？众所周知，fsm是有限状态机的那种behaviour，当然有多个不同状态，按照fsm的约定这个消息会交给“当前的状态”。

因为start_link启动fsm，然后init执行后的状态是locked，所以，上面的消息就交道locked函数！

 

其他的代码，看起来就很明白，不说了。

 

抄代码，执行一下，纯玩。