App启动流程分为2个部分，一个是系统开机，拉起Launcher APP。另一个流程分为Launcher APP点击桌面应用图标，然后启动APP。我们首先分析Launcher APP的启动。
Launcher APP的启动：
在android启动流程-SystemServer一篇文章中我们简单提过Launcher APP启动的过程，本章我们具体分析一下Launcher APP是怎么启动的。
还是先从ActivityManagerService.systemReady看起，往下执行。
ActivityManagerService
ActivityManagerService.systemReady->ActivityTaskManagerInternal.startHomeOnAllDisplays
/**
* Ready. Set. Go!
*/
public void systemReady(final Runnable goingCallback, @NonNull TimingsTraceAndSlog t) {
...
if (isBootingSystemUser && !UserManager.isHeadlessSystemUserMode()) {
t.traceBegin("startHomeOnAllDisplays");
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
t.traceEnd();
}
...
}ActivityTaskManagerService
ActivityTaskManagerInternal.startHomeOnAllDisplays->ActivityTaskManagerService.startHomeOnAllDisplays->RootWindowContainer.startHomeOnAllDisplaysex
final class LocalService extends ActivityTaskManagerInternal {
...
@Override
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
return mRootWindowContainer.startHomeOnAllDisplays(userId, reason);
}
}
...
}
RootWindowContainer
boolean startHomeOnAllDisplays(int userId, String reason) {
boolean homeStarted = false;
for (int i = getChildCount() - 1; i >= 0; i--) {
final int displayId = getChildAt(i).mDisplayId;
homeStarted |= startHomeOnDisplay(userId, reason, displayId);
}
return homeStarted;
}
boolean startHomeOnDisplay(int userId, String reason, int displayId) {
return startHomeOnDisplay(userId, reason, displayId, false /* allowInstrumenting */,
false /* fromHomeKey */);
}
boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
boolean fromHomeKey) {
// Fallback to top focused display or default display if the displayId is invalid.
if (displayId == INVALID_DISPLAY) {
final Task rootTask = getTopDisplayFocusedRootTask();
displayId = rootTask != null ? rootTask.getDisplayId() : DEFAULT_DISPLAY;
}
final DisplayContent display = getDisplayContent(displayId);
return display.reduceOnAllTaskDisplayAreas((taskDisplayArea, result) ->
result | startHomeOnTaskDisplayArea(userId, reason, taskDisplayArea,
allowInstrumenting, fromHomeKey),
false /* initValue */);
}
boolean startHomeOnTaskDisplayArea(int userId, String reason, TaskDisplayArea taskDisplayArea,boolean allowInstrumenting, boolean fromHomeKey) {
...
mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
taskDisplayArea);
return true;
}
ActivityStartController
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason,
TaskDisplayArea taskDisplayArea) {
...
mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
.setOutActivity(tmpOutRecord)
.setCallingUid(0)
.setActivityInfo(aInfo)
.setActivityOptions(options.toBundle())
.execute();
mLastHomeActivityStartRecord = tmpOutRecord[0];
if (rootHomeTask.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();
}
}我们接着看：
ActivityStarter obtainStarter(Intent intent, String reason) {
return mFactory.obtain().setIntent(intent).setReason(reason);
}
static class DefaultFactory implements Factory {
@Override
public ActivityStarter obtain() {
ActivityStarter starter = mStarterPool.acquire();
if (starter == null) {
if (mService.mRootWindowContainer == null) {
throw new IllegalStateException("Too early to start activity.");
}
starter = new ActivityStarter(mController, mService, mSupervisor, mInterceptor);
}
return starter;
}
}
int execute() {
...
try {
res = executeRequest(mRequest);
} finally {
mRequest.logMessage.append(" result code=").append(res);
Slog.i(TAG, mRequest.logMessage.toString());
mRequest.logMessage.setLength(0);
}
...
}接着看executeRequest:
private int executeRequest(Request request) {
...
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, checkedOptions,
inTask, inTaskFragment, balCode, intentGrants, realCallingUid);
if (request.outActivity != null) {
request.outActivity[0] = mLastStartActivityRecord;
}
return mLastStartActivityResult;
}private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, @BalCode int balCode,
NeededUriGrants intentGrants, int realCallingUid) {
...
try {
Trace.traceBegin(Trace.TRACE_TAG_WINDOW_MANAGER, "startActivityInner");
result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, options, inTask, inTaskFragment, balCode,
intentGrants, realCallingUid);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_WINDOW_MANAGER);
startedActivityRootTask = handleStartResult(r, options, result, newTransition,
remoteTransition);
}
...
return result;
}int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, @BalCode int balCode,
NeededUriGrants intentGrants, int realCallingUid) {
...
mRootWindowContainer.resumeFocusedTasksTopActivities(
mTargetRootTask, mStartActivity, mOptions, mTransientLaunch);
...
return START_SUCCESS;
}Launcher APP点击普通APP的启动：
ItemClickHandler:
Launcher APP点击普通APP时，会触发onClick方法：
private static void onClick(View v) {
if (tag instanceof WorkspaceItemInfo) {
onClickAppShortcut(v, (WorkspaceItemInfo) tag, launcher);
} else if (tag instanceof FolderInfo) {
if (v instanceof FolderIcon) {
onClickFolderIcon(v);
}
} else if (tag instanceof AppInfo) {
startAppShortcutOrInfoActivity(v, (AppInfo) tag, launcher);
} else if (tag instanceof LauncherAppWidgetInfo) {
if (v instanceof PendingAppWidgetHostView) {
onClickPendingWidget((PendingAppWidgetHostView) v, launcher);
}
} else if (tag instanceof ItemClickProxy) {
((ItemClickProxy) tag).onItemClicked(v);
}
}
//最终会执行到这里
private static void startAppShortcutOrInfoActivity(View v, ItemInfo item, Launcher launcher) {
...
launcher.startActivitySafely(v, intent, item);
}
然后执行到ActivityContext中：
default RunnableList startActivitySafely(
View v, Intent intent, @Nullable ItemInfo item) {
...
if (isShortcut) {
// Shortcuts need some special checks due to legacy reasons.
startShortcutIntentSafely(intent, optsBundle, item);
} else if (user == null || user.equals(Process.myUserHandle())) {
// Could be launching some bookkeeping activity
context.startActivity(intent, optsBundle);
} else {
context.getSystemService(LauncherApps.class).startMainActivity(
intent.getComponent(), user, intent.getSourceBounds(), optsBundle);
}
...
}Activity:
然后会执行到Activity.startActivity:
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
getAutofillClientController().onStartActivity(intent, mIntent);
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
// Note we want to go through this call for compatibility with
// applications that may have overridden the method.
startActivityForResult(intent, -1);
}
}
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
}
...
}然后执行Instrumentation.execStartActivity:
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
...
int result = ActivityTaskManager.getService().startActivity(whoThread,
who.getOpPackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token,
target != null ? target.mEmbeddedID : null, requestCode, 0, null, options);
...
}ActivityTaskManagerService
上面代码中ActivityTaskManager.getService()获取到ActivityTaskManagerService，所以我们接下来看ActivityTaskManagerService：
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
private int startActivityAsUser(IApplicationThread caller, String callingPackage,
@Nullable String callingFeatureId, Intent intent, String resolvedType,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
...
// TODO: Switch to user app stacks here.
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setCallingFeatureId(callingFeatureId)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(opts)
.setUserId(userId)
.execute();
}接下来的流程和Launcher APP启动流程一样了，最后附上整理了很久的流程图。供大家参考
流程图
