这一篇我们说应用程序的启动过程,上一篇插件化知识详细分解及原理 之ClassLoader及dex加载过程。 在Android系统中，应用程序是由Launcher启动起来的，其实Launcher本身也是一个应用程序，其他的应用程序安装后会在Launcher的界面上出现一个向右的图标快捷方法，点击这个图标时Launcher就好对响应的应用程序启动起来。
我们看一下Launcher的源码：路径是/packages/apps/Launcher2/src/com/android/launcher2/Launcher.java
/** * Default launcher application. */public final class Launcher extends Activity implements View.OnClickListener, OnLongClickListener, LauncherModel.Callbacks, View.OnTouchListener {首先看类的声明，Launcher继承与Activity，接着我们直接看他的点击事件
/** * Launches the intent referred by the clicked shortcut. * * @param v The view rePResenting the clicked shortcut. */public void onClick(View v) { // Make sure that rogue clicks don't get through while allapps is launching, or after the // view has detached (it's possible for this to happen if the view is removed mid touch). if (v.getWindowToken() == null) { return; } if (!mWorkspace.isFinishedSwitchingState()) { return; } Object tag = v.getTag(); if (tag instanceof ShortcutInfo) { // Open shortcut final Intent intent = ((ShortcutInfo) tag).intent; int[] pos = new int[2]; v.getLocationOnScreen(pos); intent.setSourceBounds(new Rect(pos[0], pos[1], pos[0] + v.getWidth(), pos[1] + v.getHeight())); boolean success = startActivitySafely(v, intent, tag); if (success && v instanceof BubbleTextView) { mWaitingForResume = (BubbleTextView) v; mWaitingForResume.setStayPressed(true); } } else if (tag instanceof FolderInfo) { if (v instanceof FolderIcon) { FolderIcon fi = (FolderIcon) v; handleFolderClick(fi); } } else if (v == mAllAppsButton) { if (isAllAppsVisible()) { showWorkspace(true); } else { onClickAllAppsButton(v); } }}判断如果点击的是应用快捷方式，直接调用startActivitySafely方法， 如果是Folder(应用文件夹)调用handleFolderClick方法，如果点击的是全部应用按钮调用onClickAllAppsButton(v)方法显示所有应用图标，我们直接看startActivitySafely
boolean startActivitySafely(View v, Intent intent, Object tag) { boolean success = false; try { success = startActivity(v, intent, tag); } catch (ActivityNotFoundException e) { Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show(); Log.e(TAG, "Unable to launch. tag=" + tag + " intent=" + intent, e); } return success;}直接调用了startActivity方法，上面我们看到了Luncher继承与Activity，那么我们直接再去看Activity中的startActivity方法
/** * Same as {@link #startActivity(Intent, Bundle)} with no options * specified. * * @param intent The intent to start. * * @throws android.content.ActivityNotFoundException * * @see {@link #startActivity(Intent, Bundle)} * @see #startActivityForResult */@Overridepublic void startActivity(Intent intent) { this.startActivity(intent, null);}又调用了两个参数的startActivity方法，继续跟进
@Overridepublic void startActivity(Intent intent, @Nullable Bundle options) { 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); }}走到了startActivityForResult方法，两个参数的方法最终也会调用三个参数的，我们直接看三个参数的
public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) { if (mParent == null) { Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity( this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options); if (ar != null) { mMainThread.sendActivityResult( mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData()); } if (requestCode >= 0) { // If this start is requesting a result, we can avoid making // the activity visible until the result is received. Setting // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the // activity hidden during this time, to avoid flickering. // This can only be done when a result is requested because // that guarantees we will get information back when the // activity is finished, no matter what happens to it. mStartedActivity = true; } final View decor = mWindow != null ? mWindow.peekDecorView() : null; if (decor != null) { decor.cancelPendingInputEvents(); } // TODO Consider clearing/flushing other event sources and events for child windows. } else { if (options != null) { mParent.startActivityFromChild(this, intent, requestCode, options); } else { // Note we want to go through this method for compatibility with // existing applications that may have overridden it. mParent.startActivityFromChild(this, intent, requestCode); } } if (options != null && !isTopOfTask()) { mActivityTransitionState.startExitOutTransition(this, options); }}上面的代码判断了mParent是否为空，如果不为空调用了startActivityFromChild方法，我们看一下这个方法
public void startActivityFromChild(@NonNull Activity child, Intent intent, int requestCode, @Nullable Bundle options) { Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity( this, mMainThread.getApplicationThread(), mToken, child, intent, requestCode, options); if (ar != null) { mMainThread.sendActivityResult( mToken, child.mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData()); }}这个方法和mParent为空时执行的代码一样，全都调用了Instrumentation类中的execStartActivity方法，我们进去看看这个方法
public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) { IApplicationThread whoThread = (IApplicationThread) contextThread; 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) { } return null;}最终又调用ActivityManagerNative.getDefault().startActivity方法，我们上一篇分析已经知道ActivityManagerNative.getDefault()返回的是ActivityManagerService的代理类，也就是说最终又调用了ActivityManagerService的startActivity方法，在进去看这个方法前我们先看一下 上面checkStartActivityResult方法
public static void checkStartActivityResult(int res, Object intent) { if (res >= ActivityManager.START_SUCCESS) { return; } switch (res) { case ActivityManager.START_INTENT_NOT_RESOLVED: case ActivityManager.START_CLASS_NOT_FOUND: if (intent instanceof Intent && ((Intent)intent).getComponent() != null) throw new ActivityNotFoundException( "Unable to find explicit activity class " + ((Intent)intent).getComponent().toShortString() + "; have you declared this activity in your AndroidManifest.xml?"); throw new ActivityNotFoundException( "No Activity found to handle " + intent); case ActivityManager.START_PERMISSION_DENIED: throw new SecurityException("Not allowed to start activity " + intent); case ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT: throw new AndroidRuntimeException( "FORWARD_RESULT_FLAG used while also requesting a result"); case ActivityManager.START_NOT_ACTIVITY: throw new IllegalArgumentException( "PendingIntent is not an activity"); case ActivityManager.START_NOT_VOICE_COMPATIBLE: throw new SecurityException( "Starting under voice control not allowed for: " + intent); default: throw new AndroidRuntimeException("Unknown error code " + res + " when starting " + intent); }}这个方法中抛出的异常有没有感觉非常的熟悉呢，例如have you declared this activity in your AndroidManifest.xml?，这个方法说明了我们启动Activity时会通过ActivityManagerService进行一些校检，如果不符合系统要求最终会在这里抛出异常，我们继续去找ActivityManagerService中的startActivity方法，路径： frameworks/base/services/java/com/android/server/am/ActivityManagerService.java
@Overridepublic final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) { return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId());}很简单又调用了startActivityAsUser
@Overridepublic final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) { enforceNotIsolatedCaller("startActivity"); userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId, false, ALLOW_FULL_ONLY, "startActivity", null); // TODO: Switch to user app stacks here. return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent, resolvedType, null, null, resultTo, resultWho, requestCode, startFlags, profilerInfo, null, null, bOptions, false, userId, null, null);}又调用了ActivityStarter的startActivityMayWait，他们最终和ActivityStackSupervisor类来来回回的调用，最终真正启动Activity的方法在ActivityStackSupervisor类中的realStartActivityLocked方法中，忽略其他代码，直接看启动的
//真正启动final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException { 。。。。 //调用ActivityThread的的内部类ApplicationThread类 app.thread.scheduleLaunchActivity(new Intent(r.intent), r.aPPToken, System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration), new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results, newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);}这里的会调用ActivityThread的的内部类ApplicationThread类中的scheduleLaunchActivity方法，ApplicationThread是IApplicationThread和子类，是一个Binder对象，ApplicationThread是我们应用和系统ActivityManagerService沟通的桥梁，我们在去看ActivityThread中的scheduleLaunchActivity方法
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Configuration curConfig, 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; updatePendingConfiguration(curConfig); sendMessage(H.LAUNCH_ACTIVITY, r); }非常简单，最终就发送了一个消息到ActivityThread中的内部类H中，H继承于Handler，我们去看看
public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what)); 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; 。。。 }又调用了handleLaunchActivity方法
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) { // If we are getting ready to gc after going to the background, well // we are back active so skip it. unscheduleGcIdler(); mSomeActivitiesChanged = true; if (r.profilerInfo != null) { mProfiler.setProfiler(r.profilerInfo); mProfiler.startProfiling(); } // Make sure we are running with the most recent config. handleConfigurationChanged(null, null); if (localLOGV) Slog.v( TAG, "Handling launch of " + r); // Initialize before creating the activity 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) { // The activity manager actually wants this one to start out // paused, because it needs to be visible but isn't in the // foreground. We accomplish this by going through the // normal startup (because activities expect to go through // onResume() the first time they run, before their window // is displayed), and then pausing it. However, in this case // we do -not- need to do the full pause cycle (of freezing // and such) because the activity manager assumes it can just // retain the current state it has. try { r.activity.mCalled = false; mInstrumentation.callActivityOnPause(r.activity); // We need to keep around the original state, in case // we need to be created again. But we only do this // for pre-Honeycomb apps, which always save their state // when pausing, so we can not have them save their state // when restarting from a paused state. For HC and later, // we want to (and can) let the state be saved as the normal // part of stopping the activity. if (r.isPreHoneycomb()) { r.state = oldState; } if (!r.activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPause()"); } } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { if (!mInstrumentation.onException(r.activity, e)) { throw new RuntimeException( "Unable to pause activity " + r.intent.getComponent().toShortString() + ": " + e.toString(), e); } } r.paused = true; } } else { // If there was an error, for any reason, tell the activity // manager to stop us. try { ActivityManagerNative.getDefault() .finishActivity(r.token, Activity.RESULT_CANCELED, null, false); } catch (RemoteException ex) { // Ignore } }}上面的方法中通过performLaunchActivity方法创建了Activity，然后并回调Activity响应的生命周期方法，我们去看performLaunchActivity
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")"); 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 (localLOGV) Slog.v(TAG, "Performing launch of " + r); if (localLOGV) Slog.v( TAG, r + ": app=" + app + ", appName=" + app.getPackageName() + ", pkg=" + r.packageInfo.getPackageName() + ", comp=" + r.intent.getComponent().toShortString() + ", dir=" + r.packageInfo.getAppDir()); if (activity != null) { Context appContext = createBaseContextForActivity(r, activity); CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager()); Configuration config = new Configuration(mCompatConfiguration); if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity " + r.activityInfo.name + " with config " + config); 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()"); } } } r.paused = true; mActivities.put(r.token, r); } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to start activity " + component + ": " + e.toString(), e); } } return activity;}1.上面方法的逻辑是通过Instrumentation.newActivity方法创建了Activity，
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException, IllegalaccessException, ClassNotFoundException { return (Activity)cl.loadClass(className).newInstance();}2.通过r.packageInfo.makeApplication方法判断Application是否已经创建，如果已经创建直接返回，如果没有创建则创建Application并回调onCreate方法，
public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) { if (mApplication != null) { return mApplication; } ... try { java.lang.ClassLoader cl = getClassLoader(); if (!mPackageName.equals("android")) { initializeJavaContextClassLoader(); } ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); app = mActivityThread.mInstrumentation.newApplication( cl, appClass, appContext); appContext.setOuterContext(app); } catch (Exception e) { if (!mActivityThread.mInstrumentation.onException(app, e)) { throw new RuntimeException( "Unable to instantiate application " + appClass + ": " + e.toString(), e); } } mActivityThread.mAllApplications.add(app); mApplication = app; if (instrumentation != null) { try { instrumentation.callApplicationOnCreate(app); } catch (Exception e) { if (!instrumentation.onException(app, e)) { throw new RuntimeException( "Unable to create application " + app.getClass().getName() + ": " + e.toString(), e); } } } ... } return app;}3.创建Context对象，并回调Activity的attach，onCreate方法
if (activity != null) { Context appContext = createBaseContextForActivity(r, activity); CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager()); Configuration config = new Configuration(mCompatConfiguration); if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity " + r.activityInfo.name + " with config " + config); 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); ... activity.mCalled = false; if (r.isPersistable()) { mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnCreate(activity, r.state); } ...}好了，到这里我们的应用就已经被启动起来了，我们总结一下，
1.首先我们要启动的Activity会去ActivityManagerService中去校检是否合法
2.通过回调ActivityThread中内部类ApplicationThread的scheduleLaunchActivity去发送一个消息到ActivityThread中的内部类H中，H继承于Handler
3.然后会通过反射创建Activity对象及Application对象，并回调响应生命周期方法
这里说一点ActivityManagerService和我们应用间沟通几乎都是ActivityThread，ApplicationThread，H这几个类之间来回调用，这里我们只说了onCreate的回调，其实其他生的生命周期也一样都是通过这种模式来的，而且不只是Activity，我们Android的四大组件几乎都用了这种模式，具体源码我们可以自己去看一看吧 给出几个典型的
case STOP_ACTIVITY_SHOW: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop"); handleStopActivity((IBinder)msg.obj, true, msg.arg2); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case CREATE_SERVICE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceCreate"); handleCreateService((CreateServiceData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case BIND_SERVICE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind"); handleBindService((BindServiceData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case INSTALL_PROVIDER: handleInstallProvider((ProviderInfo) msg.obj); break; case RECEIVER: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp"); handleReceiver((ReceiverData)msg.obj); maybeSnapshot(); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break;好了这篇就到这里，下一篇是我们的重点，我们前面铺垫了这么多，就是要实现插件化，动态加载一个外部未安装的apk，下一篇会通过demo一步步的来运用前面所有将过的知识来实现，而且最后会涉及动态加载资源的问题，后面会单独拿出一篇来说资源的加载,敬请期待，觉得不错就给个顶和好评吧，谢谢
新闻热点
疑难解答
