Android Framework系列–Launcher3各启动场景源码分析
Launcher3启动场景
Launcher3是Android系统提供的默认桌面应用(Launcher)，它的源码路径在“packages/apps/Launcher3/”。
Launcher3的启动场景主要包括：
- 开机后启动：开机时，android ams服务拉起Launcher
- 按键启动：比如短压home键，android wms中的PhoneWindowManager拉起Launcher
- 异常崩溃后启动：Launcher异常崩溃后，android ams再次拉起Launcher
针对这三种情况，分析一下Aosp源码如何实现。
源码基于Android10版本，时序图基于Android12（基本上与Android10的流程差不多，可以参考）。
下述说明中Launcher3和Launcher意思相同。
开机启动Launcher
Launcher的开机启动由Android的AMS服务完成。
AMS在SystemReady阶段会调用startHomeOnAllDisplays函数。Android支持多Display（虚拟Display或者由硬件上报的实际Display），多Display情况下一般Launcher会针对不同Display做不同的效果。
// frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
// 启动Home，也就是Launcher
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
}
调用ActivityTaskManagerInternal类型的接口startHomeOnAllDisplays，这个接口在ActivityTaskManagerService.java文件中实现。
// frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
final class LocalService extends ActivityTaskManagerInternal {
@Override
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
// 这个对象是RootActivityContainer类型
return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);
}
}
}
接下来调用RootActivityContainer的接口startHomeOnAllDisplays，第二个参数reson的值为“systemReady”。
// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
boolean startHomeOnAllDisplays(int userId, String reason) {
boolean homeStarted = false;
for (int i = mActivityDisplays.size() - 1; i >= 0; i--) {
final int displayId = mActivityDisplays.get(i).mDisplayId;
homeStarted |= startHomeOnDisplay(userId, reason, displayId);
}
return homeStarted;
}
遍历mActivityDisplays对于所有处于Active状态的Display调用startHomeOnDisplay，在每个Display上都启动Home（Launcher）。
// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
boolean startHomeOnDisplay(int userId, String reason, int displayId) {
// allowInstrumenting ：false
// fromHomeKey : false
return startHomeOnDisplay(userId, reason, displayId, false /* allowInstrumenting */,
false /* fromHomeKey */);
}
boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
boolean fromHomeKey) {
// 如果DisplayID是非法的，使用当前处于顶层焦点的 Display
// Fallback to top focused display if the displayId is invalid.
if (displayId == INVALID_DISPLAY) {
displayId = getTopDisplayFocusedStack().mDisplayId;
}
// 构建一个Intent
Intent homeIntent = null;
ActivityInfo aInfo = null;
if (displayId == DEFAULT_DISPLAY) {
// 如果DisplayID是默认的Display（一般是主屏）
// 调用ActivityTaskManagerService的getHomeIntent，拿到用来启动Home的Intent
homeIntent = mService.getHomeIntent();
// 查找当前系统里包含 android.intent.category.HOME的Activity。
// 择优选择使用哪个Activity
aInfo = resolveHomeActivity(userId, homeIntent);
} else if (shouldPlaceSecondaryHomeOnDisplay(displayId)) {
// 如果不是默认Display屏幕
Pair<ActivityInfo, Intent> info = resolveSecondaryHomeActivity(userId, displayId);
aInfo = info.first;
homeIntent = info.second;
}
if (aInfo == null || homeIntent == null) {
return false;
}
// 判断是否运行启动Home
if (!canStartHomeOnDisplay(aInfo, displayId, allowInstrumenting)) {
return false;
}
// 更新Home Intent
// Updates the home component of the intent.
homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
// 如果是从HomeKey启动的，添加额外参数
// Updates the extra information of the intent.
if (fromHomeKey) {
homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);
}
// Update the reason for ANR debugging to verify if the user activity is the one that
// actually launched.
final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(
aInfo.applicationInfo.uid) + ":" + displayId;
// 启动Home
mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
displayId);
return true;
}
startHomeOnDisplay函数中查询当前系统中包含 android.intent.category.HOME信息的Activity(resolveHomeActivity)，如果找到了多个Activity则选择高优先级的。根据查找的Activity信息构建Intent，使用ActivityTaskManagerService的ActivityStartController启动Home对应的Activity。
getHomeIntent函数在ActivityTaskManagerService中实现。
// frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
Intent getHomeIntent() {
// String mTopAction = Intent.ACTION_MAIN;
Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
intent.setComponent(mTopComponent);
intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
// 非FactoryTest模式下走这里。
// android.intent.category.HOME
intent.addCategory(Intent.CATEGORY_HOME);
}
return intent;
}
resolveHomeActivity函数用于查找包含android.intent.category.HOME信息的Activity。实现上是通过PMS完成的。
// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
/**
* This resolves the home activity info.
* @return the home activity info if any.
*/
@VisibleForTesting
ActivityInfo resolveHomeActivity(int userId, Intent homeIntent) {
final ComponentName comp = homeIntent.getComponent();
try {
if (comp != null) {
// Factory test.
} else {
final String resolvedType =
homeIntent.resolveTypeIfNeeded(mService.mContext.getContentResolver());
// 调用PMS查找信息
final ResolveInfo info = AppGlobals.getPackageManager()
.resolveIntent(homeIntent, resolvedType, flags, userId);
if (info != null) {
aInfo = info.activityInfo;
}
}
} catch (RemoteException e) {
// ignore
}
aInfo = new ActivityInfo(aInfo);
aInfo.applicationInfo = mService.getAppInfoForUser(aInfo.applicationInfo, userId);
return aInfo;
}
当找到所需信息后，调用ActivityStartController的startHomeActivity启动Home。该接口与AMS的startActivity和startActivityAsUser实现上基本原理一样，都是通过Intent启动Activity（fork一个进程出来）
// frameworks/base/services/core/java/com/android/server/wm/ActivityStartController.java
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason, int displayId) {
final ActivityOptions options = ActivityOptions.makeBasic();
options.setLaunchWindowingMode(WINDOWING_MODE_FULLSCREEN);
if (!ActivityRecord.isResolverActivity(aInfo.name)) {
// The resolver activity shouldn't be put in home stack because when the foreground is
// standard type activity, the resolver activity should be put on the top of current
// foreground instead of bring home stack to front.
options.setLaunchActivityType(ACTIVITY_TYPE_HOME);
}
options.setLaunchDisplayId(displayId);
// 启动Activity
mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
.setOutActivity(tmpOutRecord)
.setCallingUid(0)
.setActivityInfo(aInfo)
.setActivityOptions(options.toBundle())
.execute();
mLastHomeActivityStartRecord = tmpOutRecord[0];
final ActivityDisplay display =
mService.mRootActivityContainer.getActivityDisplay(displayId);
final ActivityStack homeStack = display != null ? display.getHomeStack() : null;
if (homeStack != null && homeStack.mInResumeTopActivity) {
// If we are in resume section already, home activity will be initialized, but not
// resumed (to avoid recursive resume) and will stay that way until something pokes it
// again. We need to schedule another resume.
mSupervisor.scheduleResumeTopActivities();
}
}
短压Home键启动Launcher
短压与长按区分，点一下Home键就属于短压。短压Home键后，Android会启动Home。
// frameworks/base/services/core/java/com/android/server/input/InputManagerService.java
// Native callback.
private long interceptKeyBeforeDispatching(IBinder focus, KeyEvent event, int policyFlags) {
// native层的 inputservice，通过这个接口上报回调
return mWindowManagerCallbacks.interceptKeyBeforeDispatching(focus, event, policyFlags);
}
// frameworks/base/services/core/java/com/android/server/wm/InputManagerCallback.java
/**
* Provides an opportunity for the window manager policy to process a key before
* ordinary dispatch.
*/
@Override
public long interceptKeyBeforeDispatching(IBinder focus, KeyEvent event, int policyFlags) {
WindowState windowState = mService.windowForClientLocked(null, focus, false);
return mService.mPolicy.interceptKeyBeforeDispatching(windowState, event, policyFlags);
}
mService是WindowManagerService类型，WindowManagerService中的mPolicy是PhoneWindowManager。PhoneWindowManager作为WMS的Policy配置文件，专门用来处理与UI行为有关的事件。PhoneWindowManager会拦截HomeKey事件进行相应处理后选择不再派发Home（PhoneWindowManager处理完就不需要其他人处理了），或者继续派发HomeKey给当前焦点View。
// frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
private long interceptKeyBeforeDispatchingInner(WindowState win, KeyEvent event,
int policyFlags) {
final boolean keyguardOn = keyguardOn();
final int keyCode = event.getKeyCode();
final int repeatCount = event.getRepeatCount();
final int metaState = event.getMetaState();
final int flags = event.getFlags();
final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
final boolean canceled = event.isCanceled();
final int displayId = event.getDisplayId();
// First we always handle the home key here, so applications
// can never break it, although if keyguard is on, we do let
// it handle it, because that gives us the correct 5 second
// timeout.
if (keyCode == KeyEvent.KEYCODE_HOME) {
// 处理HomeKey
DisplayHomeButtonHandler handler = mDisplayHomeButtonHandlers.get(displayId);
if (handler == null) {
handler = new DisplayHomeButtonHandler(displayId);
mDisplayHomeButtonHandlers.put(displayId, handler);
}
return handler.handleHomeButton(win, event);
} else if (keyCode == KeyEvent.KEYCODE_MENU) {
// 省略
}
}
/** A handler to handle home keys per display */
private class DisplayHomeButtonHandler {
int handleHomeButton(WindowState win, KeyEvent event) {
final boolean keyguardOn = keyguardOn();
final int repeatCount = event.getRepeatCount();
final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
final boolean canceled = event.isCanceled();
// If we have released the home key, and didn't do anything else
// while it was pressed, then it is time to go home!
if (!down) {
// 省略
// Post to main thread to avoid blocking input pipeline.
// 处理短压Home
mHandler.post(() -> handleShortPressOnHome(mDisplayId));
return -1;
}
// 省略
return -1;
}
}
private void handleShortPressOnHome(int displayId) {
// Turn on the connected TV and switch HDMI input if we're a HDMI playback device.
final HdmiControl hdmiControl = getHdmiControl();
if (hdmiControl != null) {
hdmiControl.turnOnTv();
}
// If there's a dream running then use home to escape the dream
// but don't actually go home.
if (mDreamManagerInternal != null && mDreamManagerInternal.isDreaming()) {
mDreamManagerInternal.stopDream(false /*immediate*/);
return;
}
// 启动Home
// Go home!
launchHomeFromHotKey(displayId);
}
PhoneWindowManager针对每个Display创建一个DisplayHomeButtonHandler ，通过它处理HomeKey。在启动Home期间如果开始了dream模式（类似于屏保），会先退出dream。最后调用launchHomeFromHotKey来启动Home，后续流程基本上与Home开机启动一致了。
Launcher异常崩溃后的自启动
Launcher意外退出（比如崩溃了）时，会触发AMS的forceStopPackage。AMS会再次将Home拉起。
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@Override
public void forceStopPackage(final String packageName, int userId) {
try {
IPackageManager pm = AppGlobals.getPackageManager();
synchronized(this) {
int[] users = userId == UserHandle.USER_ALL
? mUserController.getUsers() : new int[] {
userId };
for (int user : users) {
if (mUserController.isUserRunning(user, 0)) {
// 对每个运行的User，停掉 packageName对应的应用
forceStopPackageLocked(packageName, pkgUid, "from pid " + callingPid);
finishForceStopPackageLocked(packageName, pkgUid);
}
}
}
} finally {
Binder.restoreCallingIdentity(callingId);
}
}
forceStopPackageLocked函数中，会先Kill掉应用对应的进程。然后 resume focused app，在resume的过程中会拉起Home。
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@GuardedBy("this")
final boolean forceStopPackageLocked(String packageName, int appId,
boolean callerWillRestart, boolean purgeCache, boolean doit,
boolean evenPersistent, boolean uninstalling, int userId, String reason) {
// kill进程
boolean didSomething = mProcessList.killPackageProcessesLocked(packageName, appId, userId,
ProcessList.INVALID_ADJ, callerWillRestart, true /* allowRestart */, doit,
evenPersistent, true /* setRemoved */,
packageName == null ? ("stop user " + userId) : ("stop " + packageName));
if (doit) {
if (purgeCache && packageName != null) {
AttributeCache ac = AttributeCache.instance();
if (ac != null) {
ac.removePackage(packageName);
}
}
if (mBooted) {
// resume focused app
// 通过这个函数重新拉起Home
mAtmInternal.resumeTopActivities(true /* scheduleIdle */);
}
}
return didSomething;
}
调用ActivityTaskManagerServiced的resumeTopActivities函数。在 Home崩溃的情况下，调用这个函数，可以保证Home重新被拉起（这个函数最终会调用到RootActivityContainer 的resumeHomeActivity函数。感兴趣的可以继续顺着代码往下看）
//frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
@Override
public void resumeTopActivities(boolean scheduleIdle) {
synchronized (mGlobalLock) {
mRootActivityContainer.resumeFocusedStacksTopActivities();
if (scheduleIdle) {
mStackSupervisor.scheduleIdleLocked();
}
}
}
// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
boolean resumeFocusedStacksTopActivities(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
// 省略
if (!resumedOnDisplay) {
// In cases when there are no valid activities (e.g. device just booted or launcher
// crashed) it's possible that nothing was resumed on a display. Requesting resume
// of top activity in focused stack explicitly will make sure that at least home
// activity is started and resumed, and no recursion occurs.
final ActivityStack focusedStack = display.getFocusedStack();
if (focusedStack != null) {
focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
}
}
return result;
}