一.NavigationBar的创建
NavigationBar的创建是从StatusBar.makeStatusBarView 开始的
public class StatusBar ...{
...
protected void makeStatusBarView() {
...
try {
boolean showNav = mWindowManagerService.hasNavigationBar();
if (DEBUG) Log.v(TAG, "hasNavigationBar=" + showNav);
if (showNav) {
createNavigationBar();
}
} catch (RemoteException ex) {
// no window manager? good luck with that
}
}
...
protected void createNavigationBar() {
mNavigationBarView = NavigationBarFragment.create(mContext, (tag, fragment) -> {
mNavigationBar = (NavigationBarFragment) fragment;
if (mLightBarController != null) {
mNavigationBar.setLightBarController(mLightBarController);
}
mNavigationBar.setCurrentSysuiVisibility(mSystemUiVisibility);
});
}
...
}
在NavigationBarFragment的onCreate方法中创建了mNavigationBarView：
public class NavigationBarFragment ...{
public static View create(Context context, FragmentListener listener) {
...
View navigationBarView = LayoutInflater.from(context).inflate(
R.layout.navigation_bar_window, null);
context.getSystemService(WindowManager.class).addView(navigationBarView, lp);
NavigationBarFragment fragment = new NavigationBarFragment();
fragmentHost.getFragmentManager().beginTransaction()
.replace(R.id.navigation_bar_frame, fragment, TAG)
.commit();
...
return navigationBarView;
}
}
WindowManager添加了navigation_bar_window布局，接着新键NavigationBarFragment，NavigationBarFragment.onCreateView:
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.navigation_bar, container, false);
}
onCreateView加载了导航栏的根布局R.layout.navigation_bar.xml
<com.android.systemui.statusbar.phone.NavigationBarView
xmlns: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.NavigationBarInflaterView
android:id="@+id/navigation_inflater"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</com.android.systemui.statusbar.phone.NavigationBarView>
二.每个按钮创建流程
导航栏的容器为NavigationBarInflaterView，继承自FrameLayout：
public class NavigationBarInflaterView extends FrameLayout{
...
@Override
protected void onFinishInflate() {
super.onFinishInflate();
inflateChildren();
clearViews();
inflateLayout(getDefaultLayout());
}
...
protected String getDefaultLayout() {
final int defaultResource = mOverviewProxyService.shouldShowSwipeUpUI()
? R.string.config_navBarLayoutQuickstep
: R.string.config_navBarLayout;
return mContext.getString(defaultResource);
}
}
当NavigationBarInflaterView实例化完成之后调用了inflateLayout方法，参数由getDefaultLayout方法返回，对应的字符串在config.xml中配置：
<string name="config_navBarLayoutQuickstep" translatable="false">back[1.7WC];home;contextual[1.7WC]</string>
<string name="config_navBarLayout" translatable="false">left[.5W],back[1WC];home;recent[1WC],right[.5W]</string>
可以看到包含了back、home、recent这些字符串，那么是怎么处理的呢？
NavigationBarInflaterView.inflateLayout():
protected void inflateLayout(String newLayout) {
mCurrentLayout = newLayout;
if (newLayout == null) {
newLayout = getDefaultLayout();
}
...
//GRAVITY_SEPARATOR = ";";
String[] sets = newLayout.split(GRAVITY_SEPARATOR, 3);
//BUTTON_SEPARATOR = ",";
String[] start = sets[0].split(BUTTON_SEPARATOR);
String[] center = sets[1].split(BUTTON_SEPARATOR);
String[] end = sets[2].split(BUTTON_SEPARATOR);
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);
inflateButtons(end, mRot0.findViewById(R.id.ends_group), isRot0Landscape, false);
inflateButtons(end, mRot90.findViewById(R.id.ends_group), !isRot0Landscape, false);
...
}
可以看到先用“;”号分割得到sets,因为配置中有两个";" 所以sets为长度为3的数组，在对数组中每个字符用“，”分割得到start、center、end三个数组。分成三部分后再转入inflateButtons方法：
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);
}
}
inflateButtons遍历数组调用inflateButton方法：
@Nullable
protected View inflateButton(String buttonSpec, ViewGroup parent, boolean landscape,
boolean start) {
LayoutInflater inflater = landscape ? mLandscapeInflater : mLayoutInflater;
View v = createView(buttonSpec, parent, inflater);
if (v == null) return null;
...
return v;
}
最终每个字符传到了createView方法：
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_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);
} else if (CONTEXTUAL.equals(button)) {
v = inflater.inflate(R.layout.contextual, parent, false);
}
...
return v;
}
createView方法根据传入的字符串创建对应的布局，如home对应R.layout.home、back对应R.layout.back。。。
至此，导航栏每个按钮对应布局终于加载到了。
最后回到NavigationBarFragment.onViewCreated：
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
...
prepareNavigationBarView();
...
}
view创建完之后调用了prepareNavigationBarView方法：
private void prepareNavigationBarView() {
mNavigationBarView.reorient();
ButtonDispatcher recentsButton = mNavigationBarView.getRecentsButton();
recentsButton.setOnClickListener(this::onRecentsClick);
recentsButton.setOnTouchListener(this::onRecentsTouch);
recentsButton.setLongClickable(true);
recentsButton.setOnLongClickListener(this::onLongPressBackRecents);
ButtonDispatcher backButton = mNavigationBarView.getBackButton();
backButton.setLongClickable(true);
ButtonDispatcher homeButton = mNavigationBarView.getHomeButton();
homeButton.setOnTouchListener(this::onHomeTouch);
homeButton.setOnLongClickListener(this::onHomeLongClick);
ButtonDispatcher accessibilityButton = mNavigationBarView.getAccessibilityButton();
accessibilityButton.setOnClickListener(this::onAccessibilityClick);
accessibilityButton.setOnLongClickListener(this::onAccessibilityLongClick);
updateAccessibilityServicesState(mAccessibilityManager);
ButtonDispatcher rotateSuggestionButton = mNavigationBarView.getRotateSuggestionButton();
rotateSuggestionButton.setOnClickListener(this::onRotateSuggestionClick);
rotateSuggestionButton.setOnHoverListener(this::onRotateSuggestionHover);
updateScreenPinningGestures();
}
prepareNavigationBarView方法获取了home键、返回键及任务键，并添加了点击事件Listener。
三.总结
根据上述分析，在导航栏添加按键大致需要以下步骤：
1.修改默认布局配置config.xml中的字段：config_navBarLayout
2. NavigationBarInflaterView中，inflateLayout(String newLayout)方法中对增加的字段进行解析。
3.NavigationBarInflaterView中，inflateButton()方法处增加相应的创建Button View的方法。
4.PhoneStatusBar中，添加按键点击事件处理方法并在prepareNavigationBarView()方法中设置点击事件,设置按键可见。
5.NavigationBarView构造方法里添加到mButtonDisatchers集合，
如：mButtonDisatchers.put(R.id.back, new ButtonDispatcher(R.id.back));