Android状态机StateMachine
1.StateMachine 源码分析
1.1 StateMachine 简介
The state machine defined here is a hierarchical state machine which processes messages and can have states arranged hierarchically.
1.2 StateMachine 适用范围
-
一个对象的行为取决于它的状态，并且它必须在运行时候根据状态来改变行为；
-
一个操作中含有庞大的多分支条件语句，且这些分支依赖于该对象的状态。
在Android系统源码中，蓝牙，WIFI的状态处理就使用的StateMachine
1.3 StateMachine 作用
- 将状态封装成对象，在特定的状态下执行不同的操作，得到不同的行为模式；
- 将状态和行为封装在一起，解决庞大分支语句带来的阅读性差和不方便扩展问题，降低程序的复杂性和提升灵活性
1.4 StateMachine 各个模块的作用
1.4.1 State
public class State implements IState
{
protected State() {}
public void enter() {}
public void exit() {}
public boolean processMessage(Message msg) {}
public String getName() {}
}
状态的基类，StateMachine中的状态都是由State派生而来。
1.4.2 StateMachine
StateMachine的构造函数都是protected类型，不能实例化，都是由其子类进行初始化操作。 StateMachine有三个重载的构造函数，一个是通过指定消息循环对象来构造状态机，一个是通过指定Handler对象来构造状态机，另一个则是直接启动一个消息循环线程来构造一个状态机；他们均通过initStateMachine函数来初始化该状态机
/**
* Initialize.
*
* @param looper for this state machine
* @param name of the state machine
*/
private void initStateMachine(String name, Looper looper) {
mName = name;
mSmHandler = new SmHandler(looper, this);
}
/**
* Constructor creates a StateMachine with its own thread.
*
* @param name of the state machine
*/
protected StateMachine(String name) {
mSmThread = new HandlerThread(name);
mSmThread.start();
Looper looper = mSmThread.getLooper();
initStateMachine(name, looper);
}
/**
* Constructor creates a StateMachine using the looper.
*
* @param name of the state machine
*/
protected StateMachine(String name, Looper looper) {
initStateMachine(name, looper);
}
/**
* Constructor creates a StateMachine using the handler.
*
* @param name of the state machine
*/
protected StateMachine(String name, Handler handler) {
initStateMachine(name, handler.getLooper());
}
/**
* Add a new state to the state machine
* @param state the state to add
* @param parent the parent of state
*/
protected final void addState(State state, State parent) {
mSmHandler.addState(state, parent);
}
1.4.3 SmHandler
SmHandler是消息处理派发和状态控制切换的核心，运行在单独的线程上。
private static class SmHandler extends Handler {
...
/** State used when state machine is halted */
private HaltingState mHaltingState = new HaltingState();
/** State used when state machine is quitting */
private QuittingState mQuittingState = new QuittingState();
/** Reference to the StateMachine */
private StateMachine mSm;
/**
* Information about a state.
* Used to maintain the hierarchy.
*/
private class StateInfo {
/** The state */
State state;
/** The parent of this state, null if there is no parent */
StateInfo parentStateInfo;
/** True when the state has been entered and on the stack */
boolean active;
}
/** The map of all of the states in the state machine */
private HashMap<State, StateInfo> mStateInfo = new HashMap<State, StateInfo>();
/** The initial state that will process the first message */
private State mInitialState;
/** The destination state when transitionTo has been invoked */
private State mDestState;
/** The list of deferred messages */
private ArrayList<Message> mDeferredMessages = new ArrayList<Message>();
/**
* Constructor
*
* @param looper for dispatching messages
* @param sm the hierarchical state machine
*/
private SmHandler(Looper looper, StateMachine sm) {
super(looper);
mSm = sm;
addState(mHaltingState, null);
addState(mQuittingState, null);
}
...
SmHandler 中有三个内部类
-
StateInfo（存储当前State和其parentState，以及是否是激活状态，用来构建树形结构）
在StateMachine类中，StateInfo就是包装State组成一个Node，建立State父子关系。
private HashMap<State, StateInfo> mStateInfo = new HashMap<State, StateInfo>(); -
HaltingState和QuittingState都是从State派生，重写了processMessage方法，用于状态为停止后的逻辑处理
/**
* State entered when transitionToHaltingState is called.
*/
private class HaltingState extends State {
@Override
public boolean processMessage(Message msg) {
mSm.haltedProcessMessage(msg);
return true;
}
}
/**
* State entered when a valid quit message is handled.
*/
private class QuittingState extends State {
@Override
public boolean processMessage(Message msg) {
return NOT_HANDLED;
}
}
下面列出SmHandler核心接口实现：
/**
* Handle messages sent to the state machine by calling
* the current state's processMessage. It also handles
* the enter/exit calls and placing any deferred messages
* back onto the queue when transitioning to a new state.
*/
@Override
public final void handleMessage(Message msg) {
...
}
/**
* Do any transitions
* @param msgProcessedState is the state that processed the message
*/
private void performTransitions(State msgProcessedState, Message msg) {
...
}
/**
* Complete the construction of the state machine.
*/
private final void completeConstruction() {
...
}
/**
* Process the message. If the current state doesn't handle
* it, call the states parent and so on. If it is never handled then
* call the state machines unhandledMessage method.
* @return the state that processed the message
*/
private final State processMsg(Message msg) {
...
}
/**
* Initialize StateStack to mInitialState.
*/
private final void setupInitialStateStack() {
...
}
/**
* Add a new state to the state machine. Bottom up addition
* of states is allowed but the same state may only exist
* in one hierarchy.
*
* @param state the state to add
* @param parent the parent of state
* @return stateInfo for this state
*/
private final StateInfo addState(State state, State parent) {
...
}
/** @see StateMachine#setInitialState(State) */
private final void setInitialState(State initialState) {
...
}
/** @see StateMachine#transitionTo(IState) */
private final void transitionTo(IState destState) {
mDestState = (State) destState;
if (mDbg) mSm.log("transitionTo: destState=" + mDestState.getName());
}
/** @see StateMachine#deferMessage(Message) */
private final void deferMessage(Message msg) {
if (mDbg) mSm.log("deferMessage: msg=" + msg.what);
/* Copy the "msg" to "newMsg" as "msg" will be recycled */
Message newMsg = obtainMessage();
newMsg.copyFrom(msg);
mDeferredMessages.add(newMsg);
}
/** @see StateMachine#quit() */
private final void quit() {
if (mDbg) mSm.log("quit:");
sendMessage(obtainMessage(SM_QUIT_CMD, mSmHandlerObj));
}
/** @see StateMachine#quitNow() */
private final void quitNow() {
if (mDbg) mSm.log("quitNow:");
sendMessageAtFrontOfQueue(obtainMessage(SM_QUIT_CMD, mSmHandlerObj));
}
可以看到SmHandler是消息转发和处理的核心。
接下来根据StateMachine的标准使用流程一步一步分析：
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 {
@Override
public boolean processMessage(Message message) {
log("Hello World");
return HANDLED;
}
}
State1 mState1 = new State1();
}
void testHelloWorld() {
HelloWorld hw = makeHelloWorld();
hw.sendMessage(hw.obtainMessage());
}
1.在StateMachine初始化时，创建SmHandler对象
private void initStateMachine(String name, Looper looper) {
mName = name;
mSmHandler = new SmHandler(looper, this);
}
2.在SmHandler构造时，默认添加了mHaltingState、mQuittingState
private SmHandler(Looper looper, StateMachine sm) {
super(looper);
mSm = sm;
addState(mHaltingState, null);
addState(mQuittingState, null);
}
3.调用SmHandler的addState，格式化树形层次结构的mStateInfo
/**
* Add a new state to the state machine. Bottom up addition
* of states is allowed but the same state may only exist
* in one hierarchy.
*
* @param state the state to add
* @param parent the parent of state
* @return stateInfo for this state
*/
private final StateInfo addState(State state, State parent) {
if (mDbg) {
mSm.log("addStateInternal: E state=" + state.getName() + ",parent="
+ ((parent == null) ? "" : parent.getName()));
}
StateInfo parentStateInfo = null;
if (parent != null) {
parentStateInfo = mStateInfo.get(parent);
if (parentStateInfo == null) {
// Recursively add our parent as it's not been added yet.
parentStateInfo = addState(parent, null);
}
}
StateInfo stateInfo = mStateInfo.get(state);
if (stateInfo == null) {
stateInfo = new StateInfo();
mStateInfo.put(state, stateInfo);
}
// Validate that we aren't adding the same state in two different hierarchies.
if ((stateInfo.parentStateInfo != null)
&& (stateInfo.parentStateInfo != parentStateInfo)) {
throw new RuntimeException("state already added");
}
stateInfo.state = state;
stateInfo.parentStateInfo = parentStateInfo;
stateInfo.active = false;
if (mDbg) mSm.log("addStateInternal: X stateInfo: " + stateInfo);
return stateInfo;
}
那么目前的树形层次结构(不计mHaltingState、mQuittingState，这两个状态是负责内部逻辑处理的)中就只有mState1.
4.设置状态机状态setInitialState
/** @see StateMachine#setInitialState(State) */
private final void setInitialState(State initialState) {
if (mDbg) mSm.log("setInitialState: initialState=" + initialState.getName());
mInitialState = initialState;
}
5.StateMachine准备完毕，开始启动，调整mStateStack中各种State堆栈的次序
/**
* Start the state machine.
*/
public void start() {
// mSmHandler can be null if the state machine has quit.
SmHandler smh = mSmHandler;
if (smh == null) return;
/** Send the complete construction message */
smh.completeConstruction();
}
smh.completeConstruction()这个方法用来构建状态机运行模型
/**
* Complete the construction of the state machine.
*/
private final void completeConstruction() {
if (mDbg) mSm.log("completeConstruction: E");
/**
* Determine the maximum depth of the state hierarchy
* so we can allocate the state stacks.
*/
int maxDepth = 0;
for (StateInfo si : mStateInfo.values()) {
int depth = 0;
for (StateInfo i = si; i != null; depth++) {
i = i.parentStateInfo;
}
if (maxDepth < depth) {
maxDepth = depth;
}
}
if (mDbg) mSm.log("completeConstruction: maxDepth=" + maxDepth);
mStateStack = new StateInfo[maxDepth];
mTempStateStack = new StateInfo[maxDepth];
setupInitialStateStack();
/** Sending SM_INIT_CMD message to invoke enter methods asynchronously */
sendMessageAtFrontOfQueue(obtainMessage(SM_INIT_CMD, mSmHandlerObj));
if (mDbg) mSm.log("completeConstruction: X");
}
/**
* Initialize StateStack to mInitialState.
*/
private final void setupInitialStateStack() {
if (mDbg) {
mSm.log("setupInitialStateStack: E mInitialState=" + mInitialState.getName());
}
StateInfo curStateInfo = mStateInfo.get(mInitialState);
for (mTempStateStackCount = 0; curStateInfo != null; mTempStateStackCount++) {
mTempStateStack[mTempStateStackCount] = curStateInfo;
curStateInfo = curStateInfo.parentStateInfo;
}
// Empty the StateStack
mStateStackTopIndex = -1;
moveTempStateStackToStateStack();
}
6.StateMachine消息处理sendMessage
/**
* Enqueue a message to this state machine.
*
* Message is ignored if state machine has quit.
*/
public final void sendMessage(int what) {
// mSmHandler can be null if the state machine has quit.
SmHandler smh = mSmHandler;
if (smh == null) return;
smh.sendMessage(obtainMessage(what));
}
SmHandler是从Handler派生的，因此对应于sendMessage的是handleMessage:
/**
* Handle messages sent to the state machine by calling
* the current state's processMessage. It also handles
* the enter/exit calls and placing any deferred messages
* back onto the queue when transitioning to a new state.
*/
@Override
public final void handleMessage(Message msg) {
if (!mHasQuit) {
if (mDbg) mSm.log("handleMessage: E msg.what=" + msg.what);
/** Save the current message */
mMsg = msg;
/** State that processed the message */
State msgProcessedState = null;
if (mIsConstructionCompleted) {
/** Normal path */
msgProcessedState = processMsg(msg);
} else if (!mIsConstructionCompleted && (mMsg.what == SM_INIT_CMD)
&& (mMsg.obj == mSmHandlerObj)) {
/** Initial one time path. */
mIsConstructionCompleted = true;
invokeEnterMethods(0);
} else {
throw new RuntimeException("StateMachine.handleMessage: "
+ "The start method not called, received msg: " + msg);
}
performTransitions(msgProcessedState, msg);
// We need to check if mSm == null here as we could be quitting.
if (mDbg && mSm != null) mSm.log("handleMessage: X");
}
}
实际的消息处理调用了processMsg：
/**
* Process the message. If the current state doesn't handle
* it, call the states parent and so on. If it is never handled then
* call the state machines unhandledMessage method.
* @return the state that processed the message
*/
private final State processMsg(Message msg) {
StateInfo curStateInfo = mStateStack[mStateStackTopIndex];
if (mDbg) {
mSm.log("processMsg: " + curStateInfo.state.getName());
}
if (isQuit(msg)) {
transitionTo(mQuittingState);
} else {
while (!curStateInfo.state.processMessage(msg)) {
/**
* Not processed
*/
curStateInfo = curStateInfo.parentStateInfo;
if (curStateInfo == null) {
/**
* No parents left so it's not handled
*/
mSm.unhandledMessage(msg);
break;
}
if (mDbg) {
mSm.log("processMsg: " + curStateInfo.state.getName());
}
}
}
return (curStateInfo != null) ? curStateInfo.state : null;
}
/** Validate that the message was sent by quit or quitNow. */
private final boolean isQuit(Message msg) {
return (msg.what == SM_QUIT_CMD) && (msg.obj == mSmHandlerObj);
}
在这个函数中可以看到，如果是显示调用了quit和quitNow接口，就会把Status状态转换为mQuittingState；其他正常调用时，首先会判断当前Status是否HANDLED了消息，如果是NOT_HANDLED状态，就会递归到父类Status中处理消息。
processMessage方法中当前state先处理消息，不处理则丢给parent state，这些StateMachine对象通过同一个Handler和Loop，实现了Mesage的传递和责任链式的处理。
7.消息分发后同步状态机performTransitions
/**
* Do any transitions
* @param msgProcessedState is the state that processed the message
*/
private void performTransitions(State msgProcessedState, Message msg) {
/**
* If transitionTo has been called, exit and then enter
* the appropriate states. We loop on this to allow
* enter and exit methods to use transitionTo.
*/
State orgState = mStateStack[mStateStackTopIndex].state;
/**
* Record whether message needs to be logged before we transition and
* and we won't log special messages SM_INIT_CMD or SM_QUIT_CMD which
* always set msg.obj to the handler.
*/
boolean recordLogMsg = mSm.recordLogRec(mMsg) && (msg.obj != mSmHandlerObj);
if (mLogRecords.logOnlyTransitions()) {
/** Record only if there is a transition */
if (mDestState != null) {
mLogRecords.add(mSm, mMsg, mSm.getLogRecString(mMsg), msgProcessedState,
orgState, mDestState);
}
} else if (recordLogMsg) {
/** Record message */
mLogRecords.add(mSm, mMsg, mSm.getLogRecString(mMsg), msgProcessedState, orgState,
mDestState);
}
State destState = mDestState;
if (destState != null) {
/**
* Process the transitions including transitions in the enter/exit methods
*/
while (true) {
if (mDbg) mSm.log("handleMessage: new destination call exit/enter");
/**
* Determine the states to exit and enter and return the
* common ancestor state of the enter/exit states. Then
* invoke the exit methods then the enter methods.
*/
StateInfo commonStateInfo = setupTempStateStackWithStatesToEnter(destState);
invokeExitMethods(commonStateInfo);
int stateStackEnteringIndex = moveTempStateStackToStateStack();
invokeEnterMethods(stateStackEnteringIndex);
/**
* Since we have transitioned to a new state we need to have
* any deferred messages moved to the front of the message queue
* so they will be processed before any other messages in the
* message queue.
*/
moveDeferredMessageAtFrontOfQueue();
if (destState != mDestState) {
// A new mDestState so continue looping
destState = mDestState;
} else {
// No change in mDestState so we're done
break;
}
}
mDestState = null;
}
/**
* After processing all transitions check and
* see if the last transition was to quit or halt.
*/
if (destState != null) {
if (destState == mQuittingState) {
/**
* Call onQuitting to let subclasses cleanup.
*/
mSm.onQuitting();
cleanupAfterQuitting();
} else if (destState == mHaltingState) {
/**
* Call onHalting() if we've transitioned to the halting
* state. All subsequent messages will be processed in
* in the halting state which invokes haltedProcessMessage(msg);
*/
mSm.onHalting();
}
}
}
/** @see StateMachine#transitionTo(IState) */
private final void transitionTo(IState destState) {
mDestState = (State) destState;
if (mDbg) mSm.log("transitionTo: destState=" + mDestState.getName());
}
/** @see StateMachine#deferMessage(Message) */
private final void deferMessage(Message msg) {
if (mDbg) mSm.log("deferMessage: msg=" + msg.what);
/* Copy the "msg" to "newMsg" as "msg" will be recycled */
Message newMsg = obtainMessage();
newMsg.copyFrom(msg);
mDeferredMessages.add(newMsg);
}
/**
* Move the deferred message to the front of the message queue.
*/
private final void moveDeferredMessageAtFrontOfQueue() {
/**
* The oldest messages on the deferred list must be at
* the front of the queue so start at the back, which
* as the most resent message and end with the oldest
* messages at the front of the queue.
*/
for (int i = mDeferredMessages.size() - 1; i >= 0; i--) {
Message curMsg = mDeferredMessages.get(i);
if (mDbg) mSm.log("moveDeferredMessageAtFrontOfQueue; what=" + curMsg.what);
sendMessageAtFrontOfQueue(curMsg);
}
mDeferredMessages.clear();
}
这个阶段是Status的enter/exit逻辑处理：
private final StateInfo setupTempStateStackWithStatesToEnter(State destState) {
/**
* Search up the parent list of the destination state for an active
* state. Use a do while() loop as the destState must always be entered
* even if it is active. This can happen if we are exiting/entering
* the current state.
*/
mTempStateStackCount = 0;
StateInfo curStateInfo = mStateInfo.get(destState);
do {
mTempStateStack[mTempStateStackCount++] = curStateInfo;
curStateInfo = curStateInfo.parentStateInfo;
} while ((curStateInfo != null) && !curStateInfo.active);
if (mDbg) {
mSm.log("setupTempStateStackWithStatesToEnter: X mTempStateStackCount="
+ mTempStateStackCount + ",curStateInfo: " + curStateInfo);
}
return curStateInfo;
}
/**
* Call the exit method for each state from the top of stack
* up to the common ancestor state.
*/
private final void invokeExitMethods(StateInfo commonStateInfo) {
while ((mStateStackTopIndex >= 0)
&& (mStateStack[mStateStackTopIndex] != commonStateInfo)) {
State curState = mStateStack[mStateStackTopIndex].state;
if (mDbg) mSm.log("invokeExitMethods: " + curState.getName());
curState.exit();
mStateStack[mStateStackTopIndex].active = false;
mStateStackTopIndex -= 1;
}
}
从setupTempStateStackWithStatesToEnter可以看出查找的是当前子类State层级中的未激活的顶层父类State，而invokeExitMethods可以看出首先会调用子类State的exit()，递归调用父类State的exit()，直至匹配到指定State（注意!curStateInfo.active这个限制条件）；
/**
* Move the contents of the temporary stack to the state stack
* reversing the order of the items on the temporary stack as
* they are moved.
*
* @return index into mStateStack where entering needs to start
*/
private final int moveTempStateStackToStateStack() {
int startingIndex = mStateStackTopIndex + 1;
int i = mTempStateStackCount - 1;
int j = startingIndex;
while (i >= 0) {
if (mDbg) mSm.log("moveTempStackToStateStack: i=" + i + ",j=" + j);
mStateStack[j] = mTempStateStack[i];
j += 1;
i -= 1;
}
mStateStackTopIndex = j - 1;
if (mDbg) {
mSm.log("moveTempStackToStateStack: X mStateStackTop=" + mStateStackTopIndex
+ ",startingIndex=" + startingIndex + ",Top="
+ mStateStack[mStateStackTopIndex].state.getName());
}
return startingIndex;
}
/**
* Invoke the enter method starting at the entering index to top of state stack
*/
private final void invokeEnterMethods(int stateStackEnteringIndex) {
for (int i = stateStackEnteringIndex; i <= mStateStackTopIndex; i++) {
if (mDbg) mSm.log("invokeEnterMethods: " + mStateStack[i].state.getName());
mStateStack[i].state.enter();
mStateStack[i].active = true;
}
}
从setupInitialStateStack和moveTempStateStackToStateStack接口可知，mTempStateStack是子类在栈底模式； mStateStack是顶层父类在栈底模式；
举例一幅层级图描述如下：
State树结构层次图
那么在sendMessage前mTempStateStack的堆栈情况：
mTempStateStack堆栈状态
mStateStack的堆栈情况：
mStateStack堆栈状态
因此在此阶段是先调用顶层父类State的enter()接口，然后再递归到子类的enter()逻辑处理。
2. StateMachine 的使用
Google源码中已经将使用案例添加到源码注释中
路径如下:
frameworks\base\core\java\com\android\internal\util\StateMachine.java
/* <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 StateMachines 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>
<code>
mP1
/ \
mS2 mS1 ----> initial state
</code>
* <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 and 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 never processed
* <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>onQuiting</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</exit> 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>
<code>
mP0
/ \
mP1 mS0
/ \
mS2 mS1
/ \ \
mS3 mS4 mS5 ---> initial state
</code>
* <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>
<code>
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 {
@Override public boolean processMessage(Message message) {
log("Hello World");
return HANDLED;
}
}
State1 mState1 = new State1();
}
void testHelloWorld() {
HelloWorld hw = makeHelloWorld();
hw.sendMessage(hw.obtainMessage());
}
</code>
* <p>A more interesting state machine is one with four states
* with two independent parent states.</p>
<code>
mP1 mP2
/ \
mS2 mS1
</code>
* <p>Here is a description of this state machine using pseudo code.</p>
<code>
state mP1 {
enter { log("mP1.enter"); }
exit { log("mP1.exit"); }
on msg {
CMD_2 {
send(CMD_3);
defer(msg);
transitonTo(mS2);
return HANDLED;
}
return NOT_HANDLED;
}
}
INITIAL
state 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;
}
}
</code>
* <p>The implementation is below and also in StateMachineTest:</p>
<code>
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>
*/
若想在项目中使用StateMachine需要将源码（路径需保持一致）导入到你所需要的项目中
3.总结
StateMachine内部有个HandlerThread，SmHandler用于处理自有消息loop的消息，还有一项重要的任务就是管理StateInfo，StateInfo包含parentState的信息，Message产生的时候，交给当前的栈顶的State处理，然后交由它的parentState继续处理，parentState处理完毕后，没有更多的parentState，Message就处理完毕了。
