Android Data Analyse(4)--StateMachine

StateMachine 定义

英文定义

/* * * <p>The state machine defined here is a hierarchical state machine which processes messages * and can have states arranged hierarchically.</p> * * <p>A state is a <code>State</code> object and must implement * <code>processMessage</code> and optionally <code>enter/exit/getName</code>. * The enter/exit methods are equivalent to the construction and destruction * in Object Oriented programming and are used to perform initialization and * cleanup of the state respectively. The <code>getName</code> method returns the * name of the state; the default implementation returns the class name. It may be * desirable to have <code>getName</code> return the the state instance name instead, * in particular if a particular state class has multiple instances.</p> * * <p>When a state machine is created, <code>addState</code> is used to build the * hierarchy and <code>setInitialState</code> is used to identify which of these * is the initial state. After construction the programmer calls <code>start</code> * which initializes and starts the state machine. The first action the StateMachine * is to the invoke <code>enter</code> for all of the initial state's hierarchy, * starting at its eldest parent. The calls to enter will be done in the context * of the StateMachine's Handler, not in the context of the call to start, and they * will be invoked before any messages are processed. For example, given the simple * state machine below, mP1.enter will be invoked and then mS1.enter. Finally, * messages sent to the state machine will be processed by the current state; * in our simple state machine below that would initially be mS1.processMessage.</p><pre>        mP1       /   \      mS2   mS1 ----&gt; initial state</pre> * <p>After the state machine is created and started, messages are sent to a state * machine using <code>sendMessage</code> and the messages are created using * <code>obtainMessage</code>. When the state machine receives a message the * current state's <code>processMessage</code> is invoked. In the above example * mS1.processMessage will be invoked first. The state may use <code>transitionTo</code> * to change the current state to a new state.</p> * * <p>Each state in the state machine may have a zero or one parent states. If * a child state is unable to handle a message it may have the message processed * by its parent by returning false or NOT_HANDLED. If a message is not handled by * a child state or any of its ancestors, <code>unhandledMessage</code> will be invoked * to give one last chance for the state machine to process the message.</p> * * <p>When all processing is completed a state machine may choose to call * <code>transitionToHaltingState</code>. When the current <code>processingMessage</code> * returns the state machine will transfer to an internal <code>HaltingState</code> * and invoke <code>halting</code>. Any message subsequently received by the state * machine will cause <code>haltedProcessMessage</code> to be invoked.</p> * * <p>If it is desirable to completely stop the state machine call <code>quit</code> or * <code>quitNow</code>. These will call <code>exit</code> of the current state and its parents, * call <code>onQuitting</code> and then exit Thread/Loopers.</p> * * <p>In addition to <code>processMessage</code> each <code>State</code> has * an <code>enter</code> method and <code>exit</code> method which may be overridden.</p> * * <p>Since the states are arranged in a hierarchy transitioning to a new state * causes current states to be exited and new states to be entered. To determine * the list of states to be entered/exited the common parent closest to * the current state is found. We then exit from the current state and its * parent's up to but not including the common parent state and then enter all * of the new states below the common parent down to the destination state. * If there is no common parent all states are exited and then the new states * are entered.</p> * * <p>Two other methods that states can use are <code>deferMessage</code> and * <code>sendMessageAtFrontOfQueue</code>. The <code>sendMessageAtFrontOfQueue</code> sends * a message but places it on the front of the queue rather than the back. The * <code>deferMessage</code> causes the message to be saved on a list until a * transition is made to a new state. At which time all of the deferred messages * will be put on the front of the state machine queue with the oldest message * at the front. These will then be processed by the new current state before * any other messages that are on the queue or might be added later. Both of * these are protected and may only be invoked from within a state machine.</p> * * <p>To illustrate some of these properties we'll use state machine with an 8 * state hierarchy:</p><pre>          mP0         /   \        mP1   mS0       /   \      mS2   mS1     /  \    \    mS3  mS4  mS5  ---&gt; initial state</pre> * <p>After starting mS5 the list of active states is mP0, mP1, mS1 and mS5. * So the order of calling processMessage when a message is received is mS5, * mS1, mP1, mP0 assuming each processMessage indicates it can't handle this * message by returning false or NOT_HANDLED.</p> * * <p>Now assume mS5.processMessage receives a message it can handle, and during * the handling determines the machine should change states. It could call * transitionTo(mS4) and return true or HANDLED. Immediately after returning from * processMessage the state machine runtime will find the common parent, * which is mP1. It will then call mS5.exit, mS1.exit, mS2.enter and then * mS4.enter. The new list of active states is mP0, mP1, mS2 and mS4. So * when the next message is received mS4.processMessage will be invoked.</p> * * <p>Now for some concrete examples, here is the canonical HelloWorld as a state machine. * It responds with "Hello World" being printed to the log for every message.</p><pre>class HelloWorld extends StateMachine {    HelloWorld(String name) {        super(name);        addState(mState1);        setInitialState(mState1);    }    public static HelloWorld makeHelloWorld() {        HelloWorld hw = new HelloWorld("hw");        hw.start();        return hw;    }    class State1 extends State {        &#64;Override public boolean processMessage(Message message) {            log("Hello World");            return HANDLED;        }    }    State1 mState1 = new State1();}void testHelloWorld() {    HelloWorld hw = makeHelloWorld();    hw.sendMessage(hw.obtainMessage());}</pre> * <p>A more interesting state machine is one with four states * with two independent parent states.</p><pre>        mP1      mP2       /   \      mS2   mS1</pre> * <p>Here is a description of this state machine using pseudo code.</p> <pre>state mP1 {     enter { log("mP1.enter"); }     exit { log("mP1.exit");  }     on msg {         CMD_2 {             send(CMD_3);             defer(msg);             transitionTo(mS2);             return HANDLED;         }         return NOT_HANDLED;     }}INITIALstate mS1 parent mP1 {     enter { log("mS1.enter"); }     exit  { log("mS1.exit");  }     on msg {         CMD_1 {             transitionTo(mS1);             return HANDLED;         }         return NOT_HANDLED;     }}state mS2 parent mP1 {     enter { log("mS2.enter"); }     exit  { log("mS2.exit");  }     on msg {         CMD_2 {             send(CMD_4);             return HANDLED;         }         CMD_3 {             defer(msg);             transitionTo(mP2);             return HANDLED;         }         return NOT_HANDLED;     }}state mP2 {     enter {         log("mP2.enter");         send(CMD_5);     }     exit { log("mP2.exit"); }     on msg {         CMD_3, CMD_4 { return HANDLED; }         CMD_5 {             transitionTo(HaltingState);             return HANDLED;         }         return NOT_HANDLED;     }}</pre> * <p>The implementation is below and also in StateMachineTest:</p><pre>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 {        &#64;Override public void enter() {            log("mP1.enter");        }        &#64;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;        }        &#64;Override public void exit() {            log("mP1.exit");        }    }    class S1 extends State {        &#64;Override public void enter() {            log("mS1.enter");        }        &#64;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;            }        }        &#64;Override public void exit() {            log("mS1.exit");        }    }    class S2 extends State {        &#64;Override public void enter() {            log("mS2.enter");        }        &#64;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;        }        &#64;Override public void exit() {            log("mS2.exit");        }    }    class P2 extends State {        &#64;Override public void enter() {            log("mP2.enter");            sendMessage(obtainMessage(CMD_5));        }        &#64;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;        }        &#64;Override public void exit() {            log("mP2.exit");        }    }    &#64;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();}</pre> * <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><pre>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());     }}</pre> * <p>The output is:</p><pre>D/hsm1    ( 1999): makeHsm1 ED/hsm1    ( 1999): ctor ED/hsm1    ( 1999): ctor XD/hsm1    ( 1999): mP1.enterD/hsm1    ( 1999): mS1.enterD/hsm1    ( 1999): makeHsm1 XD/hsm1    ( 1999): mS1.processMessage what=1D/hsm1    ( 1999): mS1.exitD/hsm1    ( 1999): mS1.enterD/hsm1    ( 1999): mS1.processMessage what=2D/hsm1    ( 1999): mP1.processMessage what=2D/hsm1    ( 1999): mS1.exitD/hsm1    ( 1999): mS2.enterD/hsm1    ( 1999): mS2.processMessage what=2D/hsm1    ( 1999): mS2.processMessage what=3D/hsm1    ( 1999): mS2.exitD/hsm1    ( 1999): mP1.exitD/hsm1    ( 1999): mP2.enterD/hsm1    ( 1999): mP2.processMessage what=3D/hsm1    ( 1999): mP2.processMessage what=4D/hsm1    ( 1999): mP2.processMessage what=5D/hsm1    ( 1999): mP2.exitD/hsm1    ( 1999): halting</pre> */

中文翻译

StateMachine 能有层次的处理状态消息。
State 是某种状态的对象，它必须实现processMessage 的方法，可以选择性的实现enter()/exit()/getName()的方法。enter()/exit() 方法是为了创建和销毁State. getName ()这个方法返回该state的名字，默认返回的是state 的类名。这样可以避免一个特定的state有多个对象从而导致返回值不同。
当StateMachine被创建，将会调用addState()这个方法来创建state的层次（？），然后调用setInitialState()方法来初始化一些state.当这些完成后，会调用start()来start StateMachine. 等StateMachine初始化完毕后，从最父类型的state开始依次调用enter()。这个操作会在StateMachine的handler里面去执行而不是通过对象的调用。这个操作在所有message执行前完成。
例如：当执行mP1.enter 时，将会调用mS1.enter.最终，message 将会传递到StateMachine从而被当前的state去执行。在如下这个例子中，将会最终执行mS1.processMessage.

     mP1   /     \  mS2   mS1 ----> initial state

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