Android 导航栏虚拟按键

Android 虚拟按键

Android手机可分为有导航栏以及没导航栏两种，一般有物理按键的机器不会带有导航栏，而没有物理按键的机器则基本会带，比如华为的手机基本都是带导航栏的。当然现在全面屏手机大多都有全面屏手势，但这并不影响我们对导航栏的分析。

导航栏是如何加载到桌面上？是如何实现与物理按键相同的功能的呢？带着种种疑问，我们来read the fucking source code。

导航栏是属于系统界面的一部分，也就是SystemUI的一部分。在SystemUI中导航栏实质上是一个继承LinearLayout的ViewGroup：NavigationBarView，在系统界面初始化的时候在phone/StatusBar.java的makeStatusBarView方法中进行的

从状态栏入口函数makeStatusBarView开始看

protected void makeStatusBarView(@Nullable RegisterStatusBarResult result) {final Context context = mContext;updateDisplaySize(); // populates mDisplayMetricsupdateResources();updateTheme();inflateStatusBarWindow();//...createNavigationBar(result);}

进入 createNavigationBar 方法，发现主要是用NavigationBarController来管理

protected void createNavigationBar(@Nullable RegisterStatusBarResult result) {mNavigationBarController.createNavigationBars(true /* includeDefaultDisplay */, result);}

看NavigationBarController，调用的是NavigationBarFragment.create静态方法

public void createNavigationBars() {for (Display display : displays) {if (includeDefaultDisplay || display.getDisplayId() != DEFAULT_DISPLAY) {createNavigationBar(display, result);}}}void createNavigationBar(Display display, RegisterStatusBarResult result) {NavigationBarFragment.create(context, (tag, fragment) -> {NavigationBarFragment navBar = (NavigationBarFragment) fragment;});}

看 NavigationBarFragment 的create方法，终于知道，先载入navigation_bar_window.xml创建一个navigationBarView对象，内部就是一个NavigationBarFrame extend FrameLayout，在这个View的onViewAttachedToWindow时用来加载NavigationBarFragment对象到其中，然后是WindowManager去addView了这个导航栏的navigationBarView，触发内部的NavigationBarFragment的onCreateView来加载实际的布局。（其实SystemUI所有的模块都是WindowManager来加载View）

public static View create(Context context, FragmentListener listener) {View navigationBarView = LayoutInflater.from(context).inflate(R.layout.navigation_bar_window, null);final NavigationBarFragment fragment = FragmentHostManager.get(navigationBarView).create(NavigationBarFragment.class);navigationBarView.addOnAttachStateChangeListener(new View.OnAttachStateChangeListener() {@Overridepublic void onViewAttachedToWindow(View v) {final FragmentHostManager fragmentHost = FragmentHostManager.get(v);fragmentHost.getFragmentManager().beginTransaction().replace(R.id.navigation_bar_frame, fragment, TAG).commit();fragmentHost.addTagListener(TAG, listener);}@Overridepublic void onViewDetachedFromWindow(View v) {FragmentHostManager.removeAndDestroy(v);navigationBarView.removeOnAttachStateChangeListener(this);}});context.getSystemService(WindowManager.class).addView(navigationBarView, lp);return navigationBarView;}

navigation_bar_window.xml<com.android.systemui.statusbar.phone.NavigationBarFramexmlns:android="/apk/res/android"xmlns:systemui="/apk/res-auto"android:id="@+id/navigation_bar_frame"android:theme="@style/Theme.SystemUI"android:layout_height="match_parent"android:layout_width="match_parent"></com.android.systemui.statusbar.phone.NavigationBarFrame>

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

navigation_bar_window.xml只是多了一层嵌套，进入导航栏的真正根布局：navigation_bar.xml，好吧又是自定义view，又是嵌套结构，我们来看NavigationBarView和NavigationBarInflaterView

<com.android.systemui.statusbar.phone.NavigationBarViewxmlns:android="/apk/res/android"xmlns:systemui="/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>

来看NavigationBarView的构造方法，就是初始化了一堆ButtonDispatcher对象，这个是用来处理虚拟按键图标显示的，之后再说

public NavigationBarView(Context context, AttributeSet attrs) {super(context, attrs);mButtonDispatchers.put(R.id.back, new ButtonDispatcher(R.id.back));mButtonDispatchers.put(R.id.home, new ButtonDispatcher(R.id.home));mButtonDispatchers.put(R.id.home_handle, new ButtonDispatcher(R.id.home_handle));mButtonDispatchers.put(R.id.recent_apps, new ButtonDispatcher(R.id.recent_apps));//...}

而它实际生成NavigationBarInflaterView对象是在它的onFinishInflate方法中，NavigationBarView和NavigationBarInflaterView都是继承自View，

而onFinishInflate()方法，这是view的生命周期，每个view被inflate之后都会回调。两个类都Override了onFinishInflate方法，这个在inflate完会触发，其中NavigationBarInflaterView就在这个方法里调用inflateLayout用来创建虚拟按键布局

//NavigationBarView@Overridepublic void onFinishInflate() {super.onFinishInflate();mNavigationInflaterView = findViewById(R.id.navigation_inflater);mNavigationInflaterView.setButtonDispatchers(mButtonDispatchers);}//NavigationBarInflaterView@Overrideprotected void onFinishInflate() {super.onFinishInflate();inflateChildren();clearViews();inflateLayout(getDefaultLayout());}

我们大体看一下这个inflateLayout方法，通过getDefaultLayout获取导航栏的布局配置，然后进行解析

//NavigationInflaterViewprotected void inflateLayout(String newLayout) {mCurrentLayout = newLayout;if (newLayout == null) {newLayout = getDefaultLayout();}//解析left[.5W],back[1WC];home;recent[1WC],right[.5W]String[] sets = newLayout.split(GRAVITY_SEPARATOR, 3);if (sets.length != 3) {Log.d(TAG, "Invalid layout.");newLayout = getDefaultLayout();sets = newLayout.split(GRAVITY_SEPARATOR, 3);}//GRAVITY_SEPARATOR=";"//BUTTON_SEPARATOR=","//split字符串String[] start = sets[0].split(BUTTON_SEPARATOR);String[] center = sets[1].split(BUTTON_SEPARATOR);String[] end = sets[2].split(BUTTON_SEPARATOR);// Inflate these in start to end order or accessibility traversal will be messed up.inflateButtons(start, mHorizontal.findViewById(R.id.ends_group),false /* landscape */, true /* start */);inflateButtons(start, mVertical.findViewById(R.id.ends_group),true /* landscape */, true /* start */);inflateButtons(center, mHorizontal.findViewById(R.id.center_group),false /* landscape */, false /* start */);inflateButtons(center, mVertical.findViewById(R.id.center_group),true /* landscape */, false /* start */);inflateButtons(end, mHorizontal.findViewById(R.id.ends_group),false /* landscape */, false /* start */);inflateButtons(end, mVertical.findViewById(R.id.ends_group),true /* landscape */, false /* start */);updateButtonDispatchersCurrentView();}//获取默认导航栏布局配置protected String getDefaultLayout() {final int defaultResource = QuickStepContract.isGesturalMode(mNavBarMode)? R.string.config_navBarLayoutHandle: mOverviewProxyService.shouldShowSwipeUpUI()? R.string.config_navBarLayoutQuickstep: R.string.config_navBarLayout;return getContext().getString(defaultResource);}

下图中的三个绿框分别对应start、center、end

<!-- Nav bar button default ordering/layout --><string name="config_navBarLayout" translatable="false">left[.5W],back[1WC];home;recent[1WC],right[.5W]</string><string name="config_navBarLayoutQuickstep" translatable="false">back[1.7WC];home;contextual[1.7WC]</string><string name="config_navBarLayoutHandle" translatable="false">back[40AC];home_handle;ime_switcher[40AC]</string>

在看inflateButtons方法，调用createView创建相应View

private void inflateButtons() {for (int i = 0; i < buttons.length; i++) {inflateButton(buttons[i], parent, landscape, start);}}protected View inflateButton() {//创建相应布局View v = createView(buttonSpec, parent, inflater);//调整大小v = applySize(v, buttonSpec, landscape, start);parent.addView(v);//加到mButtonDispatchers中，设置图标addToDispatchers(v);//...return v;}private View createView() {View v = null;//提炼字符串，去掉[]，根据home，back，recent等对应不同的布局String button = extractButton(buttonSpec);if (LEFT.equals(button)) {button = extractButton(NAVSPACE);} else if (RIGHT.equals(button)) {button = extractButton(MENU_IME_ROTATE);}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_ROTATE.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;}

以HOME键为例， inflater.inflate(R.layout.home)就是解析的home.xml，返回KeyButtonView对象

//home.xml<com.android.systemui.statusbar.policy.KeyButtonViewxmlns:android="/apk/res/android"xmlns:systemui="/apk/res-auto"android:id="@+id/home"android:layout_width="@dimen/navigation_key_width"android:layout_height="match_parent"android:layout_weight="0"systemui:keyCode="3"android:scaleType="center"android:contentDescription="@string/accessibility_home"android:paddingStart="@dimen/navigation_key_padding"android:paddingEnd="@dimen/navigation_key_padding"/>

applySize主要是控制所占布局的大小，[.5W]表示0.5个weight

private static final String WEIGHT_SUFFIX = "W";private static final String WEIGHT_CENTERED_SUFFIX = "WC";private static final String ABSOLUTE_SUFFIX = "A";private static final String ABSOLUTE_VERTICAL_CENTERED_SUFFIX = "C";private View applySize(View v, String buttonSpec, boolean landscape, boolean start) {String sizeStr = extractSize(buttonSpec);if (sizeStr == null) return v;if (sizeStr.contains(WEIGHT_SUFFIX) || sizeStr.contains(ABSOLUTE_SUFFIX)) {// To support gravity, wrap in RelativeLayout and apply gravity to it.// Children wanting to use gravity must be smaller then the frame.ReverseRelativeLayout frame = new ReverseRelativeLayout(mContext);LayoutParams childParams = new LayoutParams(v.getLayoutParams());// Compute gravity to applyint gravity = (landscape) ? (start ? Gravity.TOP : Gravity.BOTTOM): (start ? Gravity.START : Gravity.END);if (sizeStr.endsWith(WEIGHT_CENTERED_SUFFIX)) {gravity = Gravity.CENTER;} else if (sizeStr.endsWith(ABSOLUTE_VERTICAL_CENTERED_SUFFIX)) {gravity = Gravity.CENTER_VERTICAL;}// Set default gravity, flipped if needed in reversed layouts (270 RTL and 90 LTR)frame.setDefaultGravity(gravity);frame.setGravity(gravity); // Apply gravity to rootframe.addView(v, childParams);if (sizeStr.contains(WEIGHT_SUFFIX)) {// Use weighting to set the width of the framefloat weight = Float.parseFloat(sizeStr.substring(0, sizeStr.indexOf(WEIGHT_SUFFIX)));frame.setLayoutParams(new LinearLayout.LayoutParams(0, MATCH_PARENT, weight));} else {int width = (int) convertDpToPx(mContext,Float.parseFloat(sizeStr.substring(0, sizeStr.indexOf(ABSOLUTE_SUFFIX))));frame.setLayoutParams(new LinearLayout.LayoutParams(width, MATCH_PARENT));}// Ensure ripples can be drawn outside boundsframe.setClipChildren(false);frame.setClipToPadding(false);return frame;}float size = Float.parseFloat(sizeStr);ViewGroup.LayoutParams params = v.getLayoutParams();params.width = (int) (params.width * size);return v;}

布局和大小都已确定，那相应的图标是怎么设置的呢？

我们来看这个addToDispatchers(v)方法，v是createView生成的KeyButtonView

private void addToDispatchers(View v) {if (mButtonDispatchers != null) {final int indexOfKey = mButtonDispatchers.indexOfKey(v.getId());if (indexOfKey >= 0) {mButtonDispatchers.valueAt(indexOfKey).addView(v);}if (v instanceof ViewGroup) {final ViewGroup viewGroup = (ViewGroup)v;final int N = viewGroup.getChildCount();for (int i = 0; i < N; i++) {addToDispatchers(viewGroup.getChildAt(i));}}}}

首先这个mButtonDispatchers是在NavigationBarView的构造方法中初始化的，然后在onFinishInflate时设置到NavigationBarInflaterView里，上面我们说过，我们以HOME为例，初始化的代码是这样的mButtonDispatchers.put(R.id.home, new ButtonDispatcher(R.id.home));

当我们addToDispatchers一个HOME View的时候，通过v.getId正好匹配到R.id.home，获取这个new ButtonDispatcher(R.id.home))，并调用它的addView方法，在方法中KeyButtonView正好 extends ImageView implements ButtonInterface，setImageDrawable其实就是调用的ImageView的setImageDrawable方法设置图片

void addView(View view) {mViews.add(view);if (view instanceof ButtonInterface) {final ButtonInterface button = (ButtonInterface) view;if (mImageDrawable != null) {button.setImageDrawable(mImageDrawable);}}}

在看这个mImageDrawable是哪来的，发现是ButtonDispatcher的setImageDrawable方法设置的，这个时候我们再回到NavigationBarView中搜索setImageDrawable方法，还是以HOME为例

public ButtonDispatcher getHomeButton() {return mButtonDispatchers.get(R.id.home);}public void updateNavButtonIcons() {KeyButtonDrawable homeIcon = mHomeDefaultIcon;getHomeButton().setImageDrawable(homeIcon);}

getHomeButton获得HOME对应的ButtonDispatcher对象，设置mHomeDefaultIcon。

对应图片资源为R.drawable.ic_sysbar_home，所以想要修改虚拟按键样式，直接替换相应资源即可

mHomeDefaultIcon = getHomeDrawable();public KeyButtonDrawable getHomeDrawable() {final boolean quickStepEnabled = mOverviewProxyService.shouldShowSwipeUpUI();KeyButtonDrawable drawable = quickStepEnabled? getDrawable(R.drawable.ic_sysbar_home_quick_step): getDrawable(R.drawable.ic_sysbar_home);orientHomeButton(drawable);return drawable;}

注意：为了方便多分辨适配，保证在高分辨率下也能显示精细画面，系统中大部分的图标资源都是矢量图，类似这样的，在替换的时候最好要求客户也提供这样的资源

ic_sysbar_home.xml<vector xmlns:android="/apk/res/android"android:width="28dp"android:height="28dp"android:viewportWidth="28"android:viewportHeight="28"><pathandroid:fillColor="?attr/singleToneColor"android:pathData="M 14 7 C 17.8659932488 7 21 10.1340067512 21 14 C 21 17.8659932488 17.8659932488 21 14 21 C 10.1340067512 21 7 17.8659932488 7 14 C 7 10.1340067512 10.1340067512 7 14 7 Z" /></vector>

而实现实际HOME按键的功能逻辑其实很简单。

当布局都加载好，我们触摸BACK键的相应区域，触发对应KeyButtonView的onTouchEvent方法

//KeyButtonViewpublic boolean onTouchEvent(MotionEvent ev) {final int action = ev.getAction();switch (action) {case MotionEvent.ACTION_DOWN:mDownTime = SystemClock.uptimeMillis();if (mCode != KEYCODE_UNKNOWN) {sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);} break;//...}return true;}

然后调用InputManager.injectInputEvent方法注入input事件，这里的mCode其实就是根据home.xml中的systemui:keyCode="3"得来的，对应KeyEvent.java中HOME键值的定义

public static final int KEYCODE_HOME = 3;

//KeyButtonViewmCode = a.getInteger(R.styleable.KeyButtonView_keyCode, KEYCODE_UNKNOWN);private void sendEvent(int action, int flags, long when) {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);mInputManager.injectInputEvent(ev, InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);}