從Android原始碼分析Activity載入流程
阿新 • • 發佈：2018-11-22
從Android原始碼分析Activity載入流程
概述：startActivity->startActivityForResult->Instrumentation::execStartActivity->scheduleLaunchActivity->performLaunchActivity->handleLaunchActivity->handleResumeActivity
本文通過Android原始碼介紹Activity的載入過程。首先從Activity.java中的startActivity開始：
@Override 可以看出startActivity也是通過呼叫startActivityForResult實現的，接下來就研究startActivityForResult的實現。
Activity.java
@Override
public void startActivityForResult(String who, Intent intent, int requestCode, @Nullable Bundle options) {
Uri referrer = onProvideReferrer();
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
Instrumentation. 這裡通過Instrumentation類的execStartActivity方法來啟動Activity。
Instrumentation.java
public ActivityResult execStartActivity(
Context who,
IBinder contextThread,
IBinder token,
Activity target,
Intent intent,
int requestCode,
Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess();
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
whoThread是一個實現了IApplicationThread介面的類的例項，IApplicationThread介面提供了系統跟應用(application)互動的API，當應用啟動的時候，application將實現了IApplicationThread介面的例項傳入Activity Manager，Activity Manager通過該例項指導應用進行諸如啟動、暫停、停止Activity等一系列操作。
public interface IApplicationThread extends IInterface {
void schedulePauseActivity(IBinder token, boolean finished, boolean userLeaving,
int configChanges, boolean dontReport) throws RemoteException;
void scheduleStopActivity(IBinder token, boolean showWindow, int configChanges) throws RemoteException;
void scheduleWindowVisibility(IBinder token, boolean showWindow) throws RemoteException;
void scheduleSleeping(IBinder token, boolean sleeping) throws RemoteException;
void scheduleResumeActivity(IBinder token, int procState, boolean isForward, Bundle resumeArgs) throws RemoteException;
void scheduleSendResult(IBinder token, List<ResultInfo> results) throws RemoteException;
void scheduleLaunchActivity(.....);
void scheduleRelaunchActivity(......);
void scheduleDestroyActivity(......);
...
}
其中啟動Activity的函式是scheduleLaunchActivity,該函式的實現在ActivityThread類的一個私有類ApplicationThread裡：
ActivityThread.java
public final class ActivityThread {
...
private class ApplicationThread extends ApplicationThreadNative {
@Override
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor, int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents, boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {
updateProcessState(procState, false);
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.referrer = referrer;
r.voiceInteractor = voiceInteractor;
r.activityInfo = info;
r.compatInfo = compatInfo;
r.state = state;
r.persistentState = persistentState;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
r.profilerInfo = profilerInfo;
r.overrideConfig = overrideConfig;
updatePendingConfiguration(curConfig);
sendMessage(H.LAUNCH_ACTIVITY, r);
}
...
}
其中ApplicationThreadNative實現了IApplicationThread介面：
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
...
}
在ApplicationThread中我們看到scheduleLaunchActivity的實現，該函式引數眾多，包括傳入Activity的intent，標識該Activity的token，儲存AndroidManifest.xml中和標記段資訊的activityInfo，儲存系統級別和使用者級別的配置curConfig（如螢幕方向，當前國家和字型縮放設定等，通過getResources().getConfiguration()獲得）等。
將這些引數賦值給ActivityClientRecord，然後通過sendMessage傳送一個型別為LAUNCH_ACTIVITY的message。
我們看看sendMessage的實現：
ActivityThread.java
private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
if (DEBUG_MESSAGES)
Slog.v(TAG, "SCHEDULE " + what + " " + mH.codeToString(what) + ": " + arg1 + " / " + obj);
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
if (async) {
msg.setAsynchronous(true);
}
mH.sendMessage(msg);
}
sendMessage就是構造了一個Message並通過H型別的Handler傳送出去。看看H的定義：
ActivityThread.java
private class H extends Handler {
public static final int LAUNCH_ACTIVITY = 100;
public static final int PAUSE_ACTIVITY = 101;
public static final int PAUSE_ACTIVITY_FINISHING= 102;
public static final int STOP_ACTIVITY_SHOW = 103;
public static final int STOP_ACTIVITY_HIDE = 104;
public static final int SHOW_WINDOW = 105;
public static final int HIDE_WINDOW = 106;
public static final int RESUME_ACTIVITY = 107;
...
public void handleMessage(Message msg) {
switch (msg.what) {
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
r.packageInfo = getPackageInfoNoCheck(r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r, null);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
break;
case RELAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityRestart");
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
handleRelaunchActivity(r);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
break;
...
}
}
...
}
在H型別的Handler裡處理了各種型別的訊息，通過函式handleLaunchActivity處理LAUNCH_ACTIVITY訊息：
ActivityThread.java
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
WindowManagerGlobal.initialize();
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward, !r.activity.mFinished && !r.startsNotResumed);
if (!r.activity.mFinished && r.startsNotResumed) {
try {
r.activity.mCalled = false;
mInstrumentation.callActivityOnPause(r.activity);
...
}
...
}
} else {
...
}
}
這裡面主要包括三個操作，performLaunchActivity啟動Activity，handleResumeActivity來Resume Activity，最後通過Instrumentation的callActivityOnPause函式來OnPause Activity。
來看看performLaunchActivity的實現：
ActivityThread.java
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo, Context.CONTEXT_INCLUDE_CODE);
}
ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity( mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity);
}
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException("Unable to instantiate activity " + component + ": " + e.toString(), e);
}
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
Context appContext = createBaseContextForActivity(r, activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mCompatConfiguration);
activity.attach(appContext, this, getInstrumentation(), r.token, r.ident, app, r.intent, r.activityInfo, title, r.parent, r.embeddedID, r.lastNonConfigurationInstances, config, r.referrer, r.voiceInteractor);
if (customIntent != null) {
activity.mIntent = customIntent;
}
r.lastNonConfigurationInstances = null;
activity.mStartedActivity = false;
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
activity.setTheme(theme);
}
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onCreate()");
}
r.activity = activity;
r.stopped = true;
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state, r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
if (!r.activity.mFinished) {
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnPostCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException("Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPostCreate()");