简介

Android系统中有3个非常重要的应用，分别是SystemUI，launcher,Setting

1. Setting：显示需要用户知道的设置项目，以前让用户配置自己系统的设置
2. launcher：显示所有的应用，展示应用入口
3. SystemUI：显示重要的信息，比如信号，电量，供用户操作的导航栏

Android 的 SystemUI 其实就是 Android 的系统界面，它包括了界面上方的状态栏 status bar，下方的导航栏Navigation Bar，锁屏界面 Keyguard ，电源界面 PowerUI，近期任务界面 Recent Task 等等。对于用户而言，SystemUI 的改动是最能直观感受到的。因此，每个 Android 版本在 SystemUI 上都有比较大的改动。而对开发者而言，理解 Android SystemUI 对优化Android系统界面，改善用户体验十分重要。

SystemUI的启动

Android系统在启动系统服务器SystemService的时候，会启动各个服务器，而在启动这个服务器之后会启动launcher和SystemUI

frameworks/base/services/java/com/android/server/SystemServer.java

public final class SystemServer { private void run() { startBootstrapServices(); startCoreServices(); startOtherServices(); } private void startOtherServices() { // We now tell the activity manager it is okay to run third party // code. It will call back into us once it has gotten to the state // where third party code can really run (but before it has actually // started launching the initial applications), for us to complete our // initialization. mActivityManagerService.systemReady(() -> { startSystemUi(context, windowManagerF); } } ｝ 

可以看出在系统在启动所有服务器之后，监听mActivityManagerService状态，如果“systemReady”后，启动SytemUI，AMS的systemReady先启动SystemUI之后启动launcher，我们这里只关注SystemUI

讯享网 static final void startSystemUi(Context context, WindowManagerService windowManager) { Intent intent = new Intent(); intent.setComponent(new ComponentName("com.android.systemui", "com.android.systemui.SystemUIService")); intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING); //Slog.d(TAG, "Starting service: " + intent); context.startServiceAsUser(intent, UserHandle.SYSTEM); windowManager.onSystemUiStarted(); } 

可以看见启动的是SystemUI的服务，然后调用 windowManager.onSystemUiStarted();

windowManager.onSystemUiStarted();执行了下面的流程

1. windowManagerSerivce#onSystemUiStarted
2. PhoneWindoiwManager#onSystemUiStarted
3. KeyguardServiceDelegate#KeyguardServiceDelegate

 public void bindService(Context context) { context.bindServiceAsUser(intent, mKeyguardConnection,//注1 Context.BIND_AUTO_CREATE, mHandler, UserHandle.SYSTEM) } 

注1：这里的intent是SystemUI的keygaurdServUC儿，通过获取SystemUI的keyguard，控制SystemU的锁屏。

SystemService启动SystemUIService

SystemUIService类十分简短，下面基本就是他全部的代码，

讯享网

讯享网public class SystemUIService extends Service { @Override public void onCreate() { super.onCreate(); ((SystemUIApplication) getApplication()).startServicesIfNeeded(); } @Override public IBinder onBind(Intent intent) { return null; } } 

他只是调用SystemUIApplication的startServicesIfNeeded方法

public class SystemUIApplication extends Application implements SysUiServiceProvider { public void startServicesIfNeeded() { String[] names = getResources().getStringArray(R.array.config_systemUIServiceComponents); startServicesIfNeeded(names); } private void startServicesIfNeeded(String[] services) { if (mServicesStarted) { return; } mServices = new SystemUI[services.length]; final int N = services.length; for (int i = 0; i < N; i++) { String clsName = services[i]; if (DEBUG) Log.d(TAG, "loading: " + clsName); log.traceBegin("StartServices" + clsName); long ti = System.currentTimeMillis(); Class cls; try { cls = Class.forName(clsName); mServices[i] = (SystemUI) cls.newInstance();//new it } catch(ClassNotFoundException ex){ throw new RuntimeException(ex); } catch (IllegalAccessException ex) { throw new RuntimeException(ex); } catch (InstantiationException ex) { throw new RuntimeException(ex); } mServices[i].mContext = this; mServices[i].mComponents = mComponents; } ｝ 

讯享网 <string-array name="config_systemUIServiceComponents" translatable="false"> <item>com.android.systemui.Dependency</item> <item>com.android.systemui.util.NotificationChannels</item> <item>com.android.systemui.statusbar.CommandQueue$CommandQueueStart</item> <item>com.android.systemui.keyguard.KeyguardViewMediator</item> <item>com.android.systemui.recents.Recents</item> <item>com.android.systemui.volume.VolumeUI</item> <item>com.android.systemui.stackdivider.Divider</item> <item>com.android.systemui.SystemBars</item> <item>com.android.systemui.usb.StorageNotification</item> <item>com.android.systemui.power.PowerUI</item> <item>com.android.systemui.media.RingtonePlayer</item> <item>com.android.systemui.keyboard.KeyboardUI</item> <item>com.android.systemui.pip.PipUI</item> <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item> <item>@string/config_systemUIVendorServiceComponent</item> <item>com.android.systemui.util.leak.GarbageMonitor$Service</item> <item>com.android.systemui.LatencyTester</item> <item>com.android.systemui.globalactions.GlobalActionsComponent</item> <item>com.android.systemui.ScreenDecorations</item> <item>com.android.systemui.fingerprint.FingerprintDialogImpl</item> <item>com.android.systemui.SliceBroadcastRelayHandler</item> </string-array> 

启动SystemBars

各个模块比较多，已SystemBars为例进行分析。在startServicesIfNeeded方法中会实例化这个模块，然后调用其start方法。

SystemBars类（去除不重要的代码，以及log）

public class SystemBars extends SystemUI { @Override public void start() { createStatusBarFromConfig(); } private void createStatusBarFromConfig() { // final String clsName =com.android.systemui.statusbar.phone.StatusBar mContext.getString(R.string.config_statusBarComponent); Class<?> cls = null; cls = mContext.getClassLoader().loadClass(clsName); mStatusBar = (SystemUI) cls.newInstance(); mStatusBar.mContext = mContext; mStatusBar.mComponents = mComponents; mStatusBar.start(); } } 

SystemBars实例化了R.string.config_statusBarComponent对应的com.android.systemui.statusbar.phone.StatusBar这个类,并调用其start方法。

讯享网public class StatusBar extends SystemUI｛ @Override public void start() { createAndAddWindows(); ｝ public void createAndAddWindows() { addStatusBarWindow(); } private void addStatusBarWindow() { makeStatusBarView(); mStatusBarWindowManager = Dependency.get(StatusBarWindowManager.class); mRemoteInputManager.setUpWithPresenter(this, mEntryManager, this, new RemoteInputController.Delegate() { public void setRemoteInputActive(NotificationData.Entry entry, boolean remoteInputActive) { mHeadsUpManager.setRemoteInputActive(entry, remoteInputActive); entry.row.notifyHeightChanged(true /* needsAnimation */); updateFooter(); } public void lockScrollTo(NotificationData.Entry entry) { mStackScroller.lockScrollTo(entry.row); } public void requestDisallowLongPressAndDismiss() { mStackScroller.requestDisallowLongPress(); mStackScroller.requestDisallowDismiss(); } }); mRemoteInputManager.getController().addCallback(mStatusBarWindowManager); mStatusBarWindowManager.add(mStatusBarWindow, getStatusBarHeight()); } protected void inflateStatusBarWindow(Context context) { mStatusBarWindow = (StatusBarWindowView) View.inflate(context, R.layout.super_status_bar, null); } ｝ 

最后通过inflateStatusBarWindow获取view，然后mStatusBarWindowManager添加这个view，并显示出来。

SystemBars加载各个视图

SystemBars加载基本全部SystemUI的界面显示，由于布局太多，查找起来十分麻烦，我从其他人那里copy过来，链接:++https://www.jianshu.com/p/2e0f403e5299++