Android 状态机stateMachine的应用

最新推荐文章于 2024-06-01 21:16:49 发布

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最新推荐文章于 2024-06-01 21:16:49 发布 · 1.7k 阅读

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本文探讨了Android源码中广泛使用的状态机概念，特别是在蓝牙、WiFi和事件处理模块中的应用。以WiFi状态机为例，从Default状态开始，详细解析了状态机的运行流程，包括enter、processMessage和exit方法的执行。StateMachine内部使用HandlerThread和SmHandler来管理消息处理，并通过StateInfo维护状态间的转换。特别指出，当Message被当前State处理后，会传递给其parentState，直到没有更多的parentState，Message处理结束。最后，以WifiStateMachine为例，展示了复杂状态转换路径的设计智慧。

研究Android源码发现很多状态机的应用，比如蓝牙，WiFi，事件处理等处，这些模块对于流程的要求很高，WiFi的连接到断开经历了一系列的操作

        addState(mDefaultState);
            addState(mInitialState, mDefaultState);
            addState(mSupplicantStartingState, mDefaultState);
            addState(mSupplicantStartedState, mDefaultState);
                addState(mDriverStartingState, mSupplicantStartedState);
                addState(mDriverStartedState, mSupplicantStartedState);
                    addState(mScanModeState, mDriverStartedState);
                    addState(mConnectModeState, mDriverStartedState);
                        addState(mL2ConnectedState, mConnectModeState);
                            addState(mObtainingIpState, mL2ConnectedState);
                            addState(mConnectedState, mL2ConnectedState);
                            addState(mRoamingState, mL2ConnectedState);
                        addState(mDisconnectingState, mConnectModeState);
                        addState(mDisconnectedState, mConnectModeState);
                        addState(mWpsRunningState, mConnectModeState);
                addState(mWaitForP2pDisableState, mSupplicantStartedState);
                addState(mDriverStoppingState, mSupplicantStartedState);
                addState(mDriverStoppedState, mSupplicantStartedState);
            addState(mSupplicantStoppingState, mDefaultState);
            addState(mSoftApState, mDefaultState);

WifiStateMachine源码里面关于WiFi状态的处理就是树状的，分层状态机，处理各种state的转化

如上图所示，WifistateMachine状态是从Default状态开始的，它的子state里面有InitialState，我们从最简单的状态分析StateMachine的运行情况。

public class State implements IState {

    /**
     * Constructor
     */
    protected State() {
    }

    /* (non-Javadoc)
     * @see com.android.internal.util.IState#enter()
     */
    @Override
    public void enter() {
    }

    /* (non-Javadoc)
     * @see com.android.internal.util.IState#exit()
     */
    @Override
    public void exit() {
    }

    /* (non-Javadoc)
     * @see com.android.internal.util.IState#processMessage(android.os.Message)
     */
    @Override
    public boolean processMessage(Message msg) {
        return false;
    }

    /**
     * Name of State for debugging purposes.
     *
     * This default implementation returns the class name, returning
     * the instance name would better in cases where a State class
     * is used for multiple states. But normally there is one class per
     * state and the class name is sufficient and easy to get. You may
     * want to provide a setName or some other mechanism for setting
     * another nam