Android Launcher啟動應用程式流程原始碼解析
阿新 • • 發佈：2019-01-07
帶著問題看原始碼
- 點選桌面Launcher圖示後做了哪些工作？
- 應用程式什麼時候被建立的？
- Application和MainActivity的onCreate()方法什麼時候被呼叫的？
概述
在Android系統中，啟動四大元件中的任何一個都可以啟動應用程式。但絕大部分時候我們是通過點選Launcher圖示啟動應用程式。本文依據Android6.0原始碼，從點選Launcher圖示，直至解析到MainActivity#OnCreate()被呼叫。
Launcher簡析
Launcher也是個應用程式，不過是個特殊的應用。俗稱“桌面”。通過PackageManagerService查詢所有已安裝的應用程式，並儲存相應的圖示、應用名稱、包名和第一個要啟動的類名等。
原始碼位置：frameworks/base/core/Java/android/app/LauncherActivity.java
LauncherActivity#onListItemClick()
public abstract classLauncherActivityextendsListActivity {
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = intentForPosition(position);
startActivity(intent);
}
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可以看到LauncherActivity繼承自ListActivity，而ListActivity繼承自Activity。在LauncherActivity#onListItemClick()方法中首先通過intentForPosition()獲取了一個Intent，然後呼叫startActivity(intent)啟動一個Activity。由於ListActivity並沒有重寫Activity#startActivity()方法，所以這裡會直接呼叫Activity#startActivity()。在此之前先看下intentForPosition()是怎樣構造Intent
protected Intent intentForPosition(int position) {
ActivityAdapter adapter = (ActivityAdapter) mAdapter;
return adapter.intentForPosition(position);
}
private classActivityAdapterextendsBaseAdapterimplementsFilterable {
public Intent intentForPosition(int position) {
if (mActivitiesList == null) {
return null;
}
Intent intent = new Intent(mIntent);
ListItem item = mActivitiesList.get(position);
intent.setClassName(item.packageName, item.className);
if (item.extras != null) {
intent.putExtras(item.extras);
}
return intent;
}
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Intent中只是指定了即將啟動的Activity。
原始碼位置：frameworks/base/core/java/android/app/Activity.java
Activity#startActivity()
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
startActivityForResult(intent, -1);
}
}
/** @param requestCode If >= 0, this code will be returned inonActivityResult() when the activity exits. */
public void startActivityForResult(Intent intent, int requestCode) {
startActivityForResult(intent, requestCode, null);
}
public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
...
}
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在呼叫的過程中可以觀察到，無論呼叫StartActivity()還是startActivityForResult()，最終呼叫的都是startActivityForResult()。而且註釋說明只有requestCode >= 0時onActivityResult()才會被呼叫。經過一系列的呼叫，最終呼叫了Instrumentation#execStartActivity()。跟進。
原始碼位置：frameworks/base/core/java/android/app/Instrumentation.java
Instrumentation#execStartActivity()
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
...
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
...
}
這裡ActivityManagerNative.getDefault()涉及到Binder程序間通訊機制。下面進行一個簡短的介紹，這不是本文的重點。瞭解過同學的可以略過下面這段Binder簡析，不想了解的也可以直接理解為返回的是ActivityManagerService（以下簡稱AMS）。實際呼叫的是AMS#startActivity()
AMS中Binder機制簡析
ActivityManagerNative.getDefault()
static public IActivityManager getDefault() {
return gDefault.get();
}
private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
IActivityManager am = asInterface(b);
return am;
}
};
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
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本例中AMS作為伺服器端，ActivityManagerNative作為客戶端。在getDefault()方法中通過呼叫asInterface()方法中的 new ActivityManagerProxy(obj)返回了IActivityManager的子類物件AMS。從哪裡可以看出來呢？這個就比較難找了，不過細心點還是可以發現寫蛛絲馬跡。重點在於IBinder b = ServiceManager.getService("activity")，這裡的引數是“activity”。在上篇博文SystemServer啟動流程原始碼解析中，分析SystemServer#startBootstrapServices()方法啟動AMS之後呼叫mActivityManagerService.setSystemProcess()，跟進。
原始碼位置：frameworks/base/services/java/com/android/server/SystemServer.java
SystemServer#startBootstrapServices()
private void startBootstrapServices() {
Installer installer = mSystemServiceManager.startService(Installer.class);
// Activity manager runs the show.
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
// Set up the Application instance for the system process and get started.
mActivityManagerService.setSystemProcess();
}
public void setSystemProcess() {
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
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靜態常量Context.ACTIVITY_SERVICE = "activity"。到這裡就對上了。先addService("activity")，然後getService("activity")。其實在add和get的時候，又是一次通過Binder進行程序間通訊的過程。這次和本文關係不大，這裡不再拓展。下面回到AMS#startActivity()
呼叫過程解析
前方高能，可能會導致身體感到嚴重不適。請做好心理準備！
原始碼位置：frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
ActivityManagerService#startActivity()
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, options,
UserHandle.getCallingUserId());
}
@Override
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
// 驗證CallingUid是否合法
enforceNotIsolatedCaller("startActivity");
// 檢查限權
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, false, userId, null, null);
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簡單驗證後開始呼叫StackSupervisor#startActivityMayWait()，跟進。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/StackSupervisor.java
StackSupervisor#startActivityMayWait()、StackSupervisor#resolveActivity()
final int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, WaitResult outResult, Configuration config,
Bundle options, boolean ignoreTargetSecurity, int userId,
IActivityContainer iContainer, TaskRecord inTask) {
...
// 解析intent資訊
ActivityInfo aInfo = resolveActivity(intent, resolvedType, startFlags, profilerInfo, userId);
// 驗證pid uid(省略)
...
int res = startActivityLocked(caller, intent, resolvedType, aInfo,
voiceSession, voiceInteractor, resultTo, resultWho,
requestCode, callingPid, callingUid, callingPackage,
realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity,
componentSpecified, null, container, inTask);
return res;
}
ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags,
ProfilerInfo profilerInfo, int userId) {
// Collect information about the target of the Intent.
ActivityInfo aInfo;
try {
ResolveInfo rInfo = AppGlobals.getPackageManager().resolveIntent(
intent, resolvedType,
PackageManager.MATCH_DEFAULT_ONLY
| ActivityManagerService.STOCK_PM_FLAGS, userId);
aInfo = rInfo != null ? rInfo.activityInfo : null;
} catch (RemoteException e) {
aInfo = null;
}
if (aInfo != null) {
intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
...
}
return aInfo;
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在呼叫resolveActivity()之後會讀取配置檔案中包名和要啟動Activity完整的路徑名，並分別賦值給aInfo.applicationInfo.packageName和aInfo.name。跟進。
StackSupervisor#startActivityLocked()
final int startActivityLocked(IApplicationThread caller,
Intent intent, String resolvedType, ActivityInfo aInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode,
int callingPid, int callingUid, String callingPackage,
int realCallingPid, int realCallingUid, int startFlags, Bundle options,
boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
ActivityContainer container, TaskRecord inTask) {
ProcessRecord callerApp = null;
if (caller != null) {
callerApp = mService.getRecordForAppLocked(caller);
if (callerApp != null) {
callingPid = callerApp.pid;
callingUid = callerApp.info.uid;
} else {
err = ActivityManager.START_PERMISSION_DENIED;
}
}
...
ActivityRecord r = new ActivityRecord(mService, callerApp, callingUid, callingPackage,
intent, resolvedType, aInfo, mService.mConfiguration, resultRecord, resultWho,
requestCode, componentSpecified, voiceSession != null, this, container, options);
// 檢查intent中的flag資訊
...
// 檢查限權
...
...
err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, true, options, inTask);
return err;
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這個方法近300行程式碼，我們只看關鍵的部分就好了。首先獲取呼叫者的pid、uid等資訊，然後儲存在callerApp中。目標Activity的資訊儲存在 r 中。跟進。
StackSupervisor#startActivityUncheckedLocked()
final int startActivityUncheckedLocked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags,
boolean doResume, Bundle options, TaskRecord inTask) {
...
int launchFlags = intent.getFlags();
// 對intent的flag各種判斷
...
ActivityRecord notTop = (launchFlags & Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP) != 0 ? r : null;
...
ActivityStack sourceStack;
if (sourceRecord != null) {
if (sourceRecord.finishing) {
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
Slog.w(TAG, "startActivity called from finishing " + sourceRecord
+ "; forcing " + "Intent.FLAG_ACTIVITY_NEW_TASK for: " + intent);
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
newTaskInfo = sourceRecord.info;
newTaskIntent = sourceRecord.task.intent;
}
sourceRecord = null;
sourceStack = null;
} else {
sourceStack = sourceRecord.task.stack;
}
} else {
sourceStack = null;
}
...
if (((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags & Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| launchSingleInstance || launchSingleTask) {
if (inTask == null && r.resultTo == null) {
// See if there is a task to bring to the front. If this is
// a SINGLE_INSTANCE activity, there can be one and only one
// instance of it in the history, and it is always in its own
// unique task, so we do a special search.
ActivityRecord intentActivity = !launchSingleInstance ?
findTaskLocked(r) : findActivityLocked(intent, r.info);
...
}
...
// Should this be considered a new task?
if (r.resultTo == null && inTask == null && !addingToTask
&& (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
targetStack = computeStackFocus(r, newTask);
targetStack.moveToFront("startingNewTask");
if (reuseTask == null) {
// 設任務棧
r.setTask(targetStack.createTaskRecord(getNextTaskId(),
newTaskInfo != null ? newTaskInfo : r.info,
newTaskIntent != null ? newTaskIntent : intent,
voiceSession, voiceInteractor, !launchTaskBehind /* toTop */),
taskToAffiliate);
}
...
}
...
targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);
return ActivityManager.START_SUCCESS;
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這個方法600+行，而且好多邏輯判斷，看的幾近崩潰。不過還好，關鍵的程式碼已經被過濾出來了～首先確定幾個變數。前面都沒有設定過intent的flag，所以launchFlags = 0x00000000，但是在執行launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK之後。launchFlags = Intent.FLAG_ACTIVITY_NEW_TASK。notTop = null。由於沒有要接收返回資訊的Activity，所以r.resultTo == null。由於沒有設定Activity的啟動模式為SingleInstance，所以launchSingleInstance = false，即會執行findTaskLocked(r)。這個方法的作用是查詢歷史所有stack中有沒有目標Activity，很顯然返回值為null，所以下面很大一段判斷邏輯都不會執行。大約200行，爽～。既然沒有相應的任務棧，肯定要建立的。在上文中建立任務棧對應的方法為targetStack.createTaskRecord()。最後執行ActivityStack#startActivityLocked()，跟進。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
ActivityStack#startActivityLocked()
final void startActivityLocked(ActivityRecord r, boolean newTask,
boolean doResume, boolean keepCurTransition, Bundle options) {
...
// newTask = true
if(!newTask){
...
}
task = r.task;
// 將ActivityRecord置於棧頂
task.addActivityToTop(r);
// 將任務棧置於前臺
task.setFrontOfTask();
...
if (doResume) {
mStackSupervisor.resumeTopActivitiesLocked(this, r, options);
}
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跟進。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/StackSupervisor.java
StackSupervisor#resumeTopActivitiesLocked()
boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,
Bundle targetOptions) {
if (targetStack == null) {
targetStack = mFocusedStack;
}
// Do targetStack first.
boolean result = false;
if (isFrontStack(targetStack)) {
result = targetStack.resumeTopActivityLocked(target, targetOptions);
}
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (stack == targetStack) {
// Already started above.
continue;
}
if (isFrontStack(stack)) {
stack.resumeTopActivityLocked(null);
}
}
}
return result;
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這個方法的作用是將Launcher應用程式所在的任務棧執行resumeTopActivityLocked()方法。跟進。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
ActivityStack#resumeTopActivityLocked()
final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {
if (mStackSupervisor.inResumeTopActivity) {
// Don't even start recursing.
return false;
}
boolean result = false;
try {
// Protect against recursion.
mStackSupervisor.inResumeTopActivity = true;
if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEAVING) {
mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN;
mService.updateSleepIfNeededLocked();
}
result = resumeTopActivityInnerLocked(prev, options);
} finally {
mStackSupervisor.inResumeTopActivity = false;
}
return result;
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跟進。
ActivityStack#resumeTopActivityInnerLocked()
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, Bundle options) {
...
// If the top activity is the resumed one, nothing to do.
if (mResumedActivity == next && next.state == ActivityState.RESUMED &&
mStackSupervisor.allResumedActivitiesComplete()) {
...
return false;
}
...
if (mResumedActivity != null) {
if (DEBUG_STATES) Slog.d(TAG_STATES,
"resumeTopActivityLocked: Pausing " + mResumedActivity);
pausing |= startPausingLocked(userLeaving, false, true, dontWaitForPause);
}
...
mStackSupervisor.startSpecificActivityLocked(next, true, true);
...
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這個方法的主要作用是將mResumedActivity暫停(Launcher任務棧的TopActivity)，即進入onPause狀態。之後啟動指定的AttivityRecored，即target AttivityRecored。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
ActivityStackSupervisor#startSpecificActivityLocked()
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
r.task.stack.setLaunchTime(r);
if (app != null && app.thread != null) {
try {
if ((r.info.flags & ActivityInfo.FLAG_MULTIPROCESS) == 0
|| !"android".equals(r.info.packageName)) {
// Don't add this if it is a platform component that is marked
// to run in multiple processes, because this is actually
// part of the framework so doesn't make sense to track as a
// separate apk in the process.
app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
mService.mProcessStats);
}
realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
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由於沒有在指定Application的process屬性，所以這裡的app = null。
詳見ActivityStackSupervisor#getProcessRecordLocked()。
final ProcessRecord getProcessRecordLocked(String processName, int uid, boolean keepIfLarge) {
if (uid == Process.SYSTEM_UID) {
// The system gets to run in any process. If there are multiple
// processes with the same uid, just pick the first (this
// should never happen).
SparseArray<ProcessRecord> procs = mProcessNames.getMap().get(processName);
if (procs == null) return null;
...
}
...
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跟進。
原始碼位置：frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
ActivityManagerService#startProcessLocked()
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType,
hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */);
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跟進。
ActivityManagerService#startProcessLocked()
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
// isolated = false
if (!isolated) {
// 沒有指定application的process，所以app = null
app = getProcessRecordLocked(processName, info.uid, keepIfLarge);
...
}
...
if (app == null) {
checkTime(startTime, "startProcess: creating new process record");
// 建立ProcessRecord
app = newProcessRecordLocked(info, processName, isolated, isolatedUid);
...
checkTime(startTime, "startProcess: done creating new process record");
}
}
...
checkTime(startTime, "startProcess: stepping in to startProcess");
// hostingNameStr="activity" 後面仨引數都是null
startProcessLocked(
app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs);
checkTime(startTime, "startProcess: done starting proc!");- 1
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終於看見Process的身影了，親人吶！！！
ActivityManagerService#startProcessLocked()
private final void startProcessLocked(ProcessRecord app, String hostingType,
String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
...
try {
int uid = app.uid;
int[] gids = null;
int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;
// isolated = false
if (!app.isolated) {
int[] permGids = null;
try {
checkTime(startTime, "startProcess: getting gids from package manager");
final IPackageManager pm = AppGlobals.getPackageManager();
permGids = pm.getPackageGids(app.info.packageName, app.userId);
MountServiceInternal mountServiceInternal = LocalServices.getService(
MountServiceInternal.class);
mountExternal = mountServiceInternal.getExternalStorageMountMode(uid,
app.info.packageName);
} catch (RemoteException e) {
throw e.rethrowAsRuntimeException();
}
/*
* Add shared application and profile GIDs so applications can share some
* resources like shared libraries and access user-wide resources
*/
if (ArrayUtils.isEmpty(permGids)) {
gids = new int[2];
} else {
gids = new int[permGids.length + 2];
System.arraycopy(permGids, 0, gids, 2, permGids.length);
}
gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid));
gids[1] = UserHandle.getUserGid(UserHandle.getUserId(uid));
}
...
String requiredAbi = (abiOverride !=