需求
基于MTK 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。
@Override
public 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。
@Override
protected 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);
}
}
@Nullable
protected 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
@Override
protected 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
- 创建一个window属性的父view
- 通过读取解析xml里config的配置，addView需要的icon,或者调换顺序
- src图片资源通过代码设置亮色和暗色
- touch事件以keycode方式交由系统处理