Android 8.1平台SystemUI 导航栏加载流程解析

本文主要是介绍Android 8.1平台SystemUI 导航栏加载流程解析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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 mDisplayMetricsupdateResources();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)

<com.android.systemui.statusbar.phone.NavigationBarFramexmlns:android="http://schemas.android.com/apk/res/android"xmlns:systemui="http://schemas.android.com/apk/res-auto"android:id="@+id/navigation_bar_frame"android:layout_height="match_parent"android:layout_width="match_parent">	</com.android.systemui.statusbar.phone.NavigationBarFrame>

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。

<com.android.systemui.statusbar.phone.NavigationBarViewxmlns:android="http://schemas.android.com/apk/res/android"xmlns:systemui="http://schemas.android.com/apk/res-auto"android:layout_height="match_parent"android:layout_width="match_parent"android:background="@drawable/system_bar_background"><com.android.systemui.statusbar.phone.NavigationBarInflaterViewandroid:id="@+id/navigation_inflater"android:layout_width="match_parent"android:layout_height="match_parent" /></com.android.systemui.statusbar.phone.NavigationBarView>

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homeString[] 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

 <!-- Nav bar button default ordering/layout -->
<string name="config_navBarLayout" translatable="false">left[.5W],back[1WC];home;recent[1WC],right[.5W]</string>

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viewif (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
<com.android.systemui.statusbar.policy.KeyButtonView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:systemui="http://schemas.android.com/apk/res-auto"
android:id="@+id/home"
android:layout_width="@dimen/navigation_key_width"//引用了dimens.xml里的navigation_key_width
android:layout_height="match_parent"
android:layout_weight="0"
systemui:keyCode="3"//systemui自定义的属性
android:scaleType="fitCenter"
android:contentDescription="@string/accessibility_home"
android:paddingTop="@dimen/home_padding"
android:paddingBottom="@dimen/home_padding"
android:paddingStart="@dimen/navigation_key_padding"
android:paddingEnd="@dimen/navigation_key_padding"/>

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。