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需求

基于MTK8163 8.1平台定制导航栏部分，在左边增加音量减，右边增加音量加

思路

需求开始做之前，一定要研读SystemUI Navigation模块的代码流程！！！不要直接去网上copy别人改的需求代码，盲改的话很容易出现问题，然而无从解决。网上有老平台（8.0-）的讲解System UI的导航栏模块的博客，自行搜索。8.0对System UI还是做了不少细节上的改动，代码改动体现上也比较多，但是总体基本流程并没变。

源码阅读可以沿着一条线索去跟代码，不要过分在乎代码细节！例如我客制化这个需求，可以跟着导航栏的返回(back)，桌面（home），最近任务（recent）中的一个功能跟代码流程，大体知道比如recen这个view是哪个方法调哪个方法最终加载出来，加载的关键代码在哪，点击事件怎么生成，而不在意里面的具体逻辑判断等等。

代码流程

1.SystemUI\src\com\android\systemui\statusbar\phone\StatusBar.java；

从状态栏入口开始看。

protected void makeStatusBarView() {    final Context context = mContext;    updateDisplaySize(); // populates mDisplayMetrics    updateResources();    updateTheme();    ...    ...     try {        boolean showNav = mWindowManagerService.hasNavigationBar();        if (DEBUG) Log.v(TAG, "hasNavigationBar=" + showNav);        if (showNav) {            createNavigationBar();//创建导航栏        }    } catch (RemoteException ex) {    }}

2.进入 createNavigationBar 方法，发现主要是用 NavigationBarFragment 来管理.

protected void createNavigationBar() {    mNavigationBarView = NavigationBarFragment.create(mContext, (tag, fragment) -> {        mNavigationBar = (NavigationBarFragment) fragment;        if (mLightBarController != null) {            mNavigationBar.setLightBarController(mLightBarController);        }        mNavigationBar.setCurrentSysuiVisibility(mSystemUiVisibility);    });}

3.看 NavigationBarFragment 的create方法，终于知道，是WindowManager去addView了导航栏的布局，最终add了fragment的onCreateView加载的布局。（其实SystemUI所有的模块都是WindowManager来加载View）

public static View create(Context context, FragmentListener listener) {    WindowManager.LayoutParams lp = new WindowManager.LayoutParams(            LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT,            WindowManager.LayoutParams.TYPE_NAVIGATION_BAR,            WindowManager.LayoutParams.FLAG_TOUCHABLE_WHEN_WAKING                    | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE                    | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL                    | WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH                    | WindowManager.LayoutParams.FLAG_SPLIT_TOUCH                    | WindowManager.LayoutParams.FLAG_SLIPPERY,            PixelFormat.TRANSLUCENT);    lp.token = new Binder();    lp.setTitle("NavigationBar");    lp.windowAnimations = 0;    View navigationBarView = LayoutInflater.from(context).inflate(            R.layout.navigation_bar_window, null);    if (DEBUG) Log.v(TAG, "addNavigationBar: about to add " + navigationBarView);    if (navigationBarView == null) return null;    context.getSystemService(WindowManager.class).addView(navigationBarView, lp);    FragmentHostManager fragmentHost = FragmentHostManager.get(navigationBarView);    NavigationBarFragment fragment = new NavigationBarFragment();    fragmentHost.getFragmentManager().beginTransaction()            .replace(R.id.navigation_bar_frame, fragment, TAG) //注意！fragment里onCreateView加载的布局是add到这个Window属性的view里的。            .commit();    fragmentHost.addTagListener(TAG, listener);    return navigationBarView;	}}

4.SystemUI\res\layout\navigation_bar_window.xml；

来看WindowManager加载的这个view的布局：navigation_bar_window.xml，发现根布局是自定义的view类NavigationBarFrame.(其实SystemUI以及其他系统应用如Launcher,都是这种自定义view的方式，好多逻辑处理也都是在自定义view里，不能忽略)

5.SystemUI\src\com\android\systemui\statusbar\phone\NavigationBarFrame.java；

我们进入NavigationBarFrame类。发现类里并不是我们的预期，就是一个FrameLayout，对DeadZone功能下的touch事件做了手脚，不管了。

6.再回来看看NavigationBarFragment的生命周期呢。onCreateView()里，导航栏的真正的rootView。

@Overridepublic View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,        Bundle savedInstanceState) {    return inflater.inflate(R.layout.navigation_bar, container, false);}

进入导航栏的真正根布局：navigation_bar.xml，好吧又是自定义view，NavigationBarView 和 NavigationBarInflaterView 都要仔细研读。

7.SystemUI\src\com\android\systemui\statusbar\phone\NavigationBarInflaterView.java；继承自FrameLayout

先看构造方法，因为加载xml布局首先走的是初始化

public NavigationBarInflaterView(Context context, AttributeSet attrs) {    super(context, attrs);    createInflaters();//根据屏幕旋转角度创建子view（单个back home or recent）的父布局    Display display = ((WindowManager)            context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();    Mode displayMode = display.getMode();    isRot0Landscape = displayMode.getPhysicalWidth() > displayMode.getPhysicalHeight();}private void inflateChildren() {    removeAllViews();    mRot0 = (FrameLayout) mLayoutInflater.inflate(R.layout.navigation_layout, this, false);    mRot0.setId(R.id.rot0);    addView(mRot0);    mRot90 = (FrameLayout) mLayoutInflater.inflate(R.layout.navigation_layout_rot90, this, false);    mRot90.setId(R.id.rot90);    addView(mRot90);    updateAlternativeOrder();}

再看onFinishInflate()方法，这是view的生命周期，每个view被inflate之后都会回调。

@Overrideprotected void onFinishInflate() {    super.onFinishInflate();    inflateChildren();//进去看无关紧要 忽略    clearViews();//进去看无关紧要 忽略    inflateLayout(getDefaultLayout());//关键方法：加载了 back.home.recent三个按钮的layout}

看inflateLayout()：里面的newLayout参数很重要！！！根据上一个方法看到getDefaultLayout()，他return了一个在xml写死的字符串。再看inflateLayout方法，他解析分割了xml里配置的字符串，并传给了inflateButtons方法

protected void inflateLayout(String newLayout) {    mCurrentLayout = newLayout;    if (newLayout == null) {        newLayout = getDefaultLayout();    }    String[] sets = newLayout.split(GRAVITY_SEPARATOR, 3);//根据“；”号分割成长度为3的数组    String[] start = sets[0].split(BUTTON_SEPARATOR);//根据“，”号分割，包含 left[.5W]和back[1WC]    String[] center = sets[1].split(BUTTON_SEPARATOR);//包含home    String[] end = sets[2].split(BUTTON_SEPARATOR);//包含recent[1WC]和right[.5W]    // Inflate these in start to end order or accessibility traversal will be messed up.    inflateButtons(start, mRot0.findViewById(R.id.ends_group), isRot0Landscape, true);    inflateButtons(start, mRot90.findViewById(R.id.ends_group), !isRot0Landscape, true);    inflateButtons(center, mRot0.findViewById(R.id.center_group), isRot0Landscape, false);    inflateButtons(center, mRot90.findViewById(R.id.center_group), !isRot0Landscape, false);    addGravitySpacer(mRot0.findViewById(R.id.ends_group));    addGravitySpacer(mRot90.findViewById(R.id.ends_group));    inflateButtons(end, mRot0.findViewById(R.id.ends_group), isRot0Landscape, false);    inflateButtons(end, mRot90.findViewById(R.id.ends_group), !isRot0Landscape, false);}    protected String getDefaultLayout() {    return mContext.getString(R.string.config_navBarLayout);}

SystemUI\res\values\config.xml

   
   
    left[.5W],back[1WC];home;recent[1WC],right[.5W]
   

再看inflateButtons()方法，遍历加载inflateButton：

private void inflateButtons(String[] buttons, ViewGroup parent, boolean landscape,        boolean start) {    for (int i = 0; i < buttons.length; i++) {        inflateButton(buttons[i], parent, landscape, start);    }}@Nullableprotected View inflateButton(String buttonSpec, ViewGroup parent, boolean landscape,        boolean start) {    LayoutInflater inflater = landscape ? mLandscapeInflater : mLayoutInflater;    View v = createView(buttonSpec, parent, inflater);//创建view    if (v == null) return null;    v = applySize(v, buttonSpec, landscape, start);    parent.addView(v);//addView到父布局    addToDispatchers(v);    View lastView = landscape ? mLastLandscape : mLastPortrait;    View accessibilityView = v;    if (v instanceof ReverseFrameLayout) {        accessibilityView = ((ReverseFrameLayout) v).getChildAt(0);    }    if (lastView != null) {        accessibilityView.setAccessibilityTraversalAfter(lastView.getId());    }    if (landscape) {        mLastLandscape = accessibilityView;    } else {        mLastPortrait = accessibilityView;    }    return v;}

我们来看createView()方法：以home按键为例，加载了home的button,其实是加载了 R.layout.home 的layout布局

private View createView(String buttonSpec, ViewGroup parent, LayoutInflater inflater) {    View v = null;    ...    ...    if (HOME.equals(button)) {        v = inflater.inflate(R.layout.home, parent, false);    } else if (BACK.equals(button)) {        v = inflater.inflate(R.layout.back, parent, false);    } else if (RECENT.equals(button)) {        v = inflater.inflate(R.layout.recent_apps, parent, false);    } else if (MENU_IME.equals(button)) {        v = inflater.inflate(R.layout.menu_ime, parent, false);    } else if (NAVSPACE.equals(button)) {        v = inflater.inflate(R.layout.nav_key_space, parent, false);    } else if (CLIPBOARD.equals(button)) {        v = inflater.inflate(R.layout.clipboard, parent, false);    }     ...    ...    return v;}//SystemUI\res\layout\home.xml //这里布局里没有src显示home的icon,肯定是在代码里设置了//这里也是自定义view:KeyButtonView
   

8.SystemUI\src\com\android\systemui\statusbar\policy\KeyButtonView.java

先来看KeyButtonView的构造方法：我们之前xml的systemui:keyCode=”3”方法在这里获取。再来看Touch事件，通过sendEvent()方法可以看出，back等view的点击touch事件不是自己处理的，而是交由系统以实体按键（keycode）的形式处理的.

当然KeyButtonView类还处理了支持长按的button,按键的响声等，这里忽略。

至此，导航栏按键事件我们梳理完毕。

public KeyButtonView(Context context, AttributeSet attrs, int defStyle) {    super(context, attrs);    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.KeyButtonView,            defStyle, 0);    mCode = a.getInteger(R.styleable.KeyButtonView_keyCode, 0);    mSupportsLongpress = a.getBoolean(R.styleable.KeyButtonView_keyRepeat, true);    mPlaySounds = a.getBoolean(R.styleable.KeyButtonView_playSound, true);    TypedValue value = new TypedValue();    if (a.getValue(R.styleable.KeyButtonView_android_contentDescription, value)) {        mContentDescriptionRes = value.resourceId;    }    a.recycle();    setClickable(true);    mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();    mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);    mRipple = new KeyButtonRipple(context, this);    setBackground(mRipple);}......public boolean onTouchEvent(MotionEvent ev) {   ...    switch (action) {        case MotionEvent.ACTION_DOWN:            mDownTime = SystemClock.uptimeMillis();            mLongClicked = false;            setPressed(true);            if (mCode != 0) {                sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);//关键方法            } else {                // Provide the same haptic feedback that the system offers for virtual keys.                performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);            }            playSoundEffect(SoundEffectConstants.CLICK);            removeCallbacks(mCheckLongPress);            postDelayed(mCheckLongPress, ViewConfiguration.getLongPressTimeout());            break;        ...        ...    }    return true;}void sendEvent(int action, int flags, long when) {    mMetricsLogger.write(new LogMaker(MetricsEvent.ACTION_NAV_BUTTON_EVENT)            .setType(MetricsEvent.TYPE_ACTION)            .setSubtype(mCode)            .addTaggedData(MetricsEvent.FIELD_NAV_ACTION, action)            .addTaggedData(MetricsEvent.FIELD_FLAGS, flags));    final int repeatCount = (flags & KeyEvent.FLAG_LONG_PRESS) != 0 ? 1 : 0;    //这里根据mCode new了一个KeyEvent事件，通过injectInputEvent使事件生效。    final KeyEvent ev = new KeyEvent(mDownTime, when, action, mCode, repeatCount,            0, KeyCharacterMap.VIRTUAL_KEYBOARD, 0,            flags | KeyEvent.FLAG_FROM_SYSTEM | KeyEvent.FLAG_VIRTUAL_HARD_KEY,            InputDevice.SOURCE_KEYBOARD);    InputManager.getInstance().injectInputEvent(ev,            InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);}

9.还遗留一个问题：设置图片的icon到底在哪？我们之前一直阅读的是NavigationBarInflaterView，根据布局我们还有一个类没有看，NavigationBarView.java

SystemUI\src\com\android\systemui\statusbar\phone\NavigationBarView.java；

进入NavigationBarView类里，找到构造方法。

public NavigationBarView(Context context, AttributeSet attrs) {    super(context, attrs);    mDisplay = ((WindowManager) context.getSystemService(            Context.WINDOW_SERVICE)).getDefaultDisplay();    ...    ...    updateIcons(context, Configuration.EMPTY, mConfiguration);//关键方法    mBarTransitions = new NavigationBarTransitions(this);    //mButtonDispatchers 是维护这些home back recent图标view的管理类，会传递到他的child,NavigationBarInflaterView类中    mButtonDispatchers.put(R.id.back, new ButtonDispatcher(R.id.back));    mButtonDispatchers.put(R.id.home, new ButtonDispatcher(R.id.home));    mButtonDispatchers.put(R.id.recent_apps, new ButtonDispatcher(R.id.recent_apps));    mButtonDispatchers.put(R.id.menu, new ButtonDispatcher(R.id.menu));    mButtonDispatchers.put(R.id.ime_switcher, new ButtonDispatcher(R.id.ime_switcher));    mButtonDispatchers.put(R.id.accessibility_button,new ButtonDispatcher(R.id.accessibility_button));} private void updateIcons(Context ctx, Configuration oldConfig, Configuration newConfig) {       ...        iconLight = mNavBarPlugin.getHomeImage(                                    ctx.getDrawable(R.drawable.ic_sysbar_home));        iconDark = mNavBarPlugin.getHomeImage(                                    ctx.getDrawable(R.drawable.ic_sysbar_home_dark));        //mHomeDefaultIcon = getDrawable(ctx,        //        R.drawable.ic_sysbar_home, R.drawable.ic_sysbar_home_dark);        mHomeDefaultIcon = getDrawable(iconLight,iconDark);        //亮色的icon资源        iconLight = mNavBarPlugin.getRecentImage(                                    ctx.getDrawable(R.drawable.ic_sysbar_recent));        //暗色的icon资源        iconDark = mNavBarPlugin.getRecentImage(                                    ctx.getDrawable(R.drawable.ic_sysbar_recent_dark));        //mRecentIcon = getDrawable(ctx,        //        R.drawable.ic_sysbar_recent, R.drawable.ic_sysbar_recent_dark);        mRecentIcon = getDrawable(iconLight,iconDark);        mMenuIcon = getDrawable(ctx, R.drawable.ic_sysbar_menu,                                    R.drawable.ic_sysbar_menu_dark);       ...       ...}

10.从第10可以看到，以recent为例，在初始化时得到了mRecentIcon的资源，再看谁调用了了mRecentIcon就可知道，即反推看调用流程。

private void updateRecentsIcon() {    getRecentsButton().setImageDrawable(mDockedStackExists ? mDockedIcon : mRecentIcon);    mBarTransitions.reapplyDarkIntensity();}

updateRecentsIcon这个方法设置了recent图片的资源，再看谁调用了updateRecentsIcon方法:onConfigurationChanged屏幕旋转会重新设置资源图片

@Overrideprotected void onConfigurationChanged(Configuration newConfig) {    super.onConfigurationChanged(newConfig);    boolean uiCarModeChanged = updateCarMode(newConfig);    updateTaskSwitchHelper();    updateIcons(getContext(), mConfiguration, newConfig);    updateRecentsIcon();    if (uiCarModeChanged || mConfiguration.densityDpi != newConfig.densityDpi            || mConfiguration.getLayoutDirection() != newConfig.getLayoutDirection()) {        // If car mode or density changes, we need to reset the icons.        setNavigationIconHints(mNavigationIconHints, true);    }    mConfiguration.updateFrom(newConfig);}public void setNavigationIconHints(int hints, boolean force) {    ...    ...    mNavigationIconHints = hints;    // We have to replace or restore the back and home button icons when exiting or entering    // carmode, respectively. Recents are not available in CarMode in nav bar so change    // to recent icon is not required.    KeyButtonDrawable backIcon = (backAlt)            ? getBackIconWithAlt(mUseCarModeUi, mVertical)            : getBackIcon(mUseCarModeUi, mVertical);    getBackButton().setImageDrawable(backIcon);    updateRecentsIcon();    ...    ...}

reorient()也调用了setNavigationIconHints()方法：

public void reorient() {    updateCurrentView();    ...    setNavigationIconHints(mNavigationIconHints, true);    getHomeButton().setVertical(mVertical);}

再朝上推，最终追溯到NavigationBarFragment的onConfigurationChanged()方法 和 NavigationBarView的onAttachedToWindow()和onSizeChanged()方法。也就是说，在NavigationBarView导航栏这个布局加载的时候就会设置图片资源，和长度改变，屏幕旋转都有可能引起重新设置

至此，SystemUI的虚拟导航栏模块代码流程结束。

总结

1. 创建一个window属性的父view
2. 通过读取解析xml里config的配置，addView需要的icon,或者调换顺序
3. src图片资源通过代码设置亮色和暗色
4. touch事件以keycode方式交由系统处理

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