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Android 状态机的样例代码.md
  // 状态分层结构设定
    mP1      mP2
   /   \
  mS2   mS1
class Hsm1 extends StateMachine {
    public static final int CMD_1 = 1;
    public static final int CMD_2 = 2;
    public static final int CMD_3 = 3;
    public static final int CMD_4 = 4;
    public static final int CMD_5 = 5;

    public static Hsm1 makeHsm1() {
        log("makeHsm1 E");
        Hsm1 sm = new Hsm1("hsm1");
        sm.start();
        log("makeHsm1 X");
        return sm;
    }

    Hsm1(String name) {
        super(name);
        log("ctor E");

        // Add states, use indentation to show hierarchy
        addState(mP1);
            addState(mS1, mP1);
            addState(mS2, mP1);
        addState(mP2);

        // Set the initial state
        setInitialState(mS1);
        log("ctor X");
    }

    class P1 extends State {
        @Override public void enter() {
            log("mP1.enter");
        }
        @Override public boolean processMessage(Message message) {
            boolean retVal;
            log("mP1.processMessage what=" + message.what);
            switch(message.what) {
            case CMD_2:
                // CMD_2 will arrive in mS2 before CMD_3
                sendMessage(obtainMessage(CMD_3));
                deferMessage(message);
                transitionTo(mS2);
                retVal = HANDLED;
                break;
            default:
                // Any message we don't understand in this state invokes unhandledMessage
                retVal = NOT_HANDLED;
                break;
            }
            return retVal;
        }
        @Override public void exit() {
            log("mP1.exit");
        }
    }

    class S1 extends State {
        @Override public void enter() {
            log("mS1.enter");
        }
        @Override public boolean processMessage(Message message) {
            log("S1.processMessage what=" + message.what);
            if (message.what == CMD_1) {
                // Transition to ourself to show that enter/exit is called
                transitionTo(mS1);
                return HANDLED;
            } else {
                // Let parent process all other messages
                return NOT_HANDLED;
            }
        }
        @Override public void exit() {
            log("mS1.exit");
        }
    }

    class S2 extends State {
        @Override public void enter() {
            log("mS2.enter");
        }
        @Override public boolean processMessage(Message message) {
            boolean retVal;
            log("mS2.processMessage what=" + message.what);
            switch(message.what) {
            case(CMD_2):
                sendMessage(obtainMessage(CMD_4));
                retVal = HANDLED;
                break;
            case(CMD_3):
                deferMessage(message);
                transitionTo(mP2);
                retVal = HANDLED;
                break;
            default:
                retVal = NOT_HANDLED;
                break;
            }
            return retVal;
        }
        @Override public void exit() {
            log("mS2.exit");
        }
    }

    class P2 extends State {
        @Override public void enter() {
            log("mP2.enter");
            sendMessage(obtainMessage(CMD_5));
        }
        @Override public boolean processMessage(Message message) {
            log("P2.processMessage what=" + message.what);
            switch(message.what) {
            case(CMD_3):
                break;
            case(CMD_4):
                break;
            case(CMD_5):
                transitionToHaltingState();
                break;
            }
            return HANDLED;
        }
        @Override public void exit() {
            log("mP2.exit");
        }
    }

    @Override
    void onHalting() {
        log("halting");
        synchronized (this) {
            this.notifyAll();
        }
    }

    P1 mP1 = new P1();
    S1 mS1 = new S1();
    S2 mS2 = new S2();
    P2 mP2 = new P2();
}

</code>
 * <p>If this is executed by sending two messages CMD_1 and CMD_2
 * (Note the synchronize is only needed because we use hsm.wait())</p>
<code>
Hsm1 hsm = makeHsm1();
synchronize(hsm) {
     hsm.sendMessage(obtainMessage(hsm.CMD_1));
     hsm.sendMessage(obtainMessage(hsm.CMD_2));
     try {
          // wait for the messages to be handled
          hsm.wait();
     } catch (InterruptedException e) {
          loge("exception while waiting " + e.getMessage());
     }
}
</code>
 * <p>The output is:</p>
<code>
D/hsm1    ( 1999): makeHsm1 E
D/hsm1    ( 1999): ctor E
D/hsm1    ( 1999): ctor X
D/hsm1    ( 1999): mP1.enter
D/hsm1    ( 1999): mS1.enter
D/hsm1    ( 1999): makeHsm1 X
D/hsm1    ( 1999): mS1.processMessage what=1
D/hsm1    ( 1999): mS1.exit
D/hsm1    ( 1999): mS1.enter
D/hsm1    ( 1999): mS1.processMessage what=2
D/hsm1    ( 1999): mP1.processMessage what=2
D/hsm1    ( 1999): mS1.exit
D/hsm1    ( 1999): mS2.enter
D/hsm1    ( 1999): mS2.processMessage what=2
D/hsm1    ( 1999): mS2.processMessage what=3
D/hsm1    ( 1999): mS2.exit
D/hsm1    ( 1999): mP1.exit
D/hsm1    ( 1999): mP2.enter
D/hsm1    ( 1999): mP2.processMessage what=3
D/hsm1    ( 1999): mP2.processMessage what=4
D/hsm1    ( 1999): mP2.processMessage what=5
D/hsm1    ( 1999): mP2.exit
D/hsm1    ( 1999): halting
</code>

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