做企业网站开发哪家好,使用网站效果,怎么修改网站内容,有没有专门发布毕业设计代做网站关于作者#xff1a;CSDN内容合伙人、技术专家#xff0c; 从零开始做日活千万级APP。 专注于分享各领域原创系列文章 #xff0c;擅长java后端、移动开发、人工智能等#xff0c;希望大家多多支持。 目录 一、概览二、应用内启动源码流程 (startActivity)2.1 startActivit… 关于作者CSDN内容合伙人、技术专家 从零开始做日活千万级APP。 专注于分享各领域原创系列文章 擅长java后端、移动开发、人工智能等希望大家多多支持。 目录 一、概览二、应用内启动源码流程 (startActivity)2.1 startActivity()2.2 startActivityAsUser()2.3 startActivityUnchecked()2.4 resumeFocusedStackTopActivityLocked()2.5 startSpecificActivityLocked - realStartActivityLocked() 三、 Activity实例化过程四、 setContentView五、 后续生命周期六、 推荐阅读 学习前建议有相关知识储备 【Android 基础】 应用Application启动流程
通过本文你可以学习到Activity启动流程。
一、概览
Activity 是 android 四大组件之一很有必要知道它的启动过程我们在上一篇文章中介绍了 APP的启动流程里面大概讲到了Activity的 启动流程在本文中我们系统的再总结一下当成一个记录。
Activity 的启动方式我们讲有两种一种是在应用内部启动另一种是外部启动比如Launcher
应用内启动 通过 startActivity、startActivityForResult等方式来启动 Activity
其流程我们总结下
1、调用 Activity 的 startActivity 方法来启动目标 Activity 2、接着就会调用到 Instrunmentation 的 execStartActivity 方法然后调用到 AMS 的 startActivity 中去 3、调用到 AMS 中后会执行到ActivityStarter 的 execute 方法接着就会进行一些校验和判断权限包括进程检查intent检查权限检查、是否启用新栈等 4、所有的信息存储在ActivityRecord中ActivityRecord是Activity在system_server进程中的镜像Activity实例与ActivityRecord实例一一对应。ActivityRecord用来存储Activity的信息如所在的进程名称应用的包名所在的任务栈的taskAffinity等 5、中间再经过一系列调用又回调到 ActivityThread 的 handleLaunchActivity 来启动 Activity。
借用一张网络图片
应用外启动 通过Launcher 进程启动Launcher 就是我们桌面程序当系统开机后 Launcher 也随之被启动。
1、fork并调用ActivityThread的main方法创建app进程 2、然后从 ActivityThread 调用到AMS中的attachApplicationLocked创建Application 3、Application创建完后调用ActivityStackSupervisor的attachApplicationLocked方法最终调用到handleLaunchActivity进行activity的创建
二、应用内启动源码流程 (startActivity)
我们就从源码出发一起来看看startActivity后面的流程
2.1 startActivity()
Activity.java Overridepublic void startActivity(Intent intent) {this.startActivity(intent, null);}Overridepublic void startActivity(Intent intent, Nullable Bundle options) {if (options ! null) {startActivityForResult(intent, -1, options);} else {startActivityForResult(intent, -1);}}public void startActivityForResult(RequiresPermission Intent intent, int requestCode) {startActivityForResult(intent, requestCode, null);} 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);if (ar ! null) {//分析启动结果mMainThread.sendActivityResult(mToken, mEmbeddedID, requestCode, ar.getResultCode(),ar.getResultData());}} else {// 最终也是调用 execStartActivity 方法源码如下if (options ! null) {mParent.startActivityFromChild(this, intent, requestCode, options);} else {mParent.startActivityFromChild(this, intent, requestCode);}}}public void startActivityFromChild(NonNull Activity child, RequiresPermission Intent intent,int requestCode, Nullable Bundle options) {options transferSpringboardActivityOptions(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());}cancelInputsAndStartExitTransition(options);}上面代码中最终都会调用了 execStartActivity 方法该方法会返回一个启动结果。我们一起来看看 frameworks/base/core/java/android/app/Instrumentation.java
/**** param who 用来启动 Activity 的对象* param contextThread Binder 对象具有跨进程通信的能力传入的是 ApplicationThread* param token Binder 对象指向了服务端一个 ActivityRecord 对象* param target 当前的 Activity* param intent Intent 对象* param requestCode 请求码*/public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, String target,Intent intent, int requestCode, Bundle options) {IApplicationThread whoThread (IApplicationThread) contextThread;try {intent.migrateExtraStreamToClipData();intent.prepareToLeaveProcess(who);// 这里的service 就是 ActivityManagerService 具体可以跟代码看到 // 这么一句 ServiceManager.getService(Context.ACTIVITY_SERVICE);int result ActivityManager.getService().startActivity(whoThread, who.getBasePackageName(), intent,intent.resolveTypeIfNeeded(who.getContentResolver()),token, target, requestCode, 0, null, options);checkStartActivityResult(result, intent);} catch (RemoteException e) {}return null;}通过 Binder 调用 AMS 启动 Activity我们接着往下看
2.2 startActivityAsUser()
ActivityManagerService.java public class ActivityManagerService extends IActivityManager.StubOverridepublic 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());}public 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,boolean validateIncomingUser) {enforceNotIsolatedCaller(startActivity);// 首先 检查调用者权限userId mActivityStartController.checkTargetUser(userId, validateIncomingUser,Binder.getCallingPid(), Binder.getCallingUid(), startActivityAsUser);// TODO: Switch to user app stacks here.return mActivityStartController.obtainStarter(intent, startActivityAsUser).setCaller(caller).setCallingPackage(callingPackage).setResolvedType(resolvedType).setResultTo(resultTo).setResultWho(resultWho).setRequestCode(requestCode).setStartFlags(startFlags).setProfilerInfo(profilerInfo).setActivityOptions(bOptions).setMayWait(userId).execute();}最后调用的是 ActivityStarter.execute();
上面代码最终调用到了 startActivityAsUser 方法在内部将所有点的参数都交给了 ActivityStarter
2.3 startActivityUnchecked()
ActivityStarter 该类包含了启动的所有逻辑比如 Intent 解析以及任务栈等。
ActivityStarter.java int execute() {try {if (mRequest.mayWait) {return startActivityMayWait(mRequest.caller, ...);} else {// todo return startActivity(mRequest.caller, ...); }} finally {onExecutionComplete();}}private int startActivity(IApplicationThread caller, Intent intent, ...) {// 再次检查调用者权限包括进程检查intent检查权限检查等boolean abort !mSupervisor.checkStartAnyActivityPermission(intent, aInfo, ...);abort | !mService.mIntentFirewall.checkStartActivity(intent, ...);// 每个 Activity 都会对应一个 ActivityRecord 对象ActivityRecord r new ActivityRecord(mService, ...);// todo result startActivityUnchecked(r, sourceRecord ...);}// Note: This method should only be called from {link startActivity}.private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord ...) {//设置初始化状态setInitialState(r, options, inTask, ...);//判断启动模式并且在 mLaunchFlags 上追加对应标记computeLaunchingTaskFlags();//设置 Activity 的栈computeSourceStack();//设置 LaunchFlags 到 intent 上mIntent.setFlags(mLaunchFlags);//决定是否用新的栈ActivityRecord reusedActivity getReusableIntentActivity();...// Should this be considered a new task?int result START_SUCCESS;if (mStartActivity.resultTo null mInTask null !mAddingToTask (mLaunchFlags FLAG_ACTIVITY_NEW_TASK) ! 0) {newTask true;// 创建一个新的task来启动result setTaskFromReuseOrCreateNewTask(taskToAffiliate, topStack);} else// todo mSupervisor.resumeFocusedStackTopActivityLocked(); }上面代码中会进行一些校验和判断权限包括进程检查intent检查权限检查等
2.4 resumeFocusedStackTopActivityLocked()
ActivityStackSupervisor.java
boolean resumeFocusedStackTopActivityLocked(ActivityStack targetStack...) {return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);return false;}
resumeTopActivityUncheckedLocked - resumeTopActivityInnerLocked - startSpecificActivityLocked() ActivityStack.java
GuardedBy(mService)boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {if (mStackSupervisor.inResumeTopActivity) {Activity 存在则resumetransaction.setLifecycleStateRequest( ResumeActivityItem.obtain(next.app.repProcState,。。。);mService.getLifecycleManager().scheduleTransaction(transaction);不存在则调用下面这个result resumeTopActivityInnerLocked(prev, options);} finally {}return result;}GuardedBy(mService)private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {mStackSupervisor.startSpecificActivityLocked(next, true, false);return true;}2.5 startSpecificActivityLocked - realStartActivityLocked()
ActivityStackSupervisor.java startSpecificActivityLocked - realStartActivityLocked(); 到这个地方我们就可以看到真的开始启动 activity 后面就跟Application 里面一样了
void startSpecificActivityLocked(ActivityRecord r ...) {if (app ! null app.thread ! null) {try {// 真的开始启动 activity ,看下面的方法realStartActivityLocked(r, app, andResume, checkConfig);return;} catch (RemoteException e) {}}}真的开始启动 activityfinal boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,boolean andResume, boolean checkConfig) throws RemoteException {// Create activity launch transaction.final ClientTransaction clientTransaction ClientTransaction.obtain(app.thread,r.appToken);clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),System.identityHashCode(r), r.info,// TODO: Have this take the merged configuration instead of separate global// and override configs.mergedConfiguration.getGlobalConfiguration(),mergedConfiguration.getOverrideConfiguration(), r.compat,r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,r.persistentState, results, newIntents, mService.isNextTransitionForward(),profilerInfo));// Schedule transaction.mService.getLifecycleManager().scheduleTransaction(clientTransaction);}ActivityManagerService
ClientLifecycleManager getLifecycleManager() {return mLifecycleManager;}
ClientLifecycleManager 通过代码我们可以看到获取的client就是 ActivityThreadIApplicationThread是一个AIDL文件void scheduleTransaction(ClientTransaction transaction) throws RemoteException {final IApplicationThread client transaction.getClient();transaction.schedule();}ClientTransaction /** Target client. */private IApplicationThread mClient;public void schedule() throws RemoteException {mClient.scheduleTransaction(this);}ClientTransactionHandler
//ActivityThread中没有复写scheduleTransaction会执行到父类的方法//public final class ActivityThread extends ClientTransactionHandler//ClientTransactionHandler.javapublic abstract class ClientTransactionHandler {void scheduleTransaction(ClientTransaction transaction) {transaction.preExecute(this);//发送消息sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);}}ActivityThread.java
case EXECUTE_TRANSACTION:final ClientTransaction transaction (ClientTransaction) msg.obj;mTransactionExecutor.execute(transaction);break;
这里其实就是执行LaunchActivityItem的execute方法 其赋值的地方在realStartActivityLocked()方法大家可以回头看看前面有这么一句代码 clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
TransactionExecutor.java
public void execute(ClientTransaction transaction) {final IBinder token transaction.getActivityToken();executeCallbacks(transaction);executeLifecycleState(transaction);mPendingActions.clear();log(End resolving transaction);}/** Cycle through all states requested by callbacks and execute them at proper times. */VisibleForTestingpublic void executeCallbacks(ClientTransaction transaction) {final ListClientTransactionItem callbacks transaction.getCallbacks();final IBinder token transaction.getActivityToken();ActivityClientRecord r mTransactionHandler.getActivityClient(token);final ActivityLifecycleItem finalStateRequest transaction.getLifecycleStateRequest();final int size callbacks.size();for (int i 0; i size; i) {final ClientTransactionItem item callbacks.get(i);item.execute(mTransactionHandler, token, mPendingActions);item.postExecute(mTransactionHandler, token, mPendingActions);}}到这里就调用到我们熟悉的handleLaunchActivity了 LaunchActivityItem.java
Overridepublic void execute(ClientTransactionHandler client, IBinder token,PendingTransactionActions pendingActions) {ActivityClientRecord r new ActivityClientRecord(token, mIntent, mIdent, mInfo,mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,mPendingResults, mPendingNewIntents, mIsForward,mProfilerInfo, client);client.handleLaunchActivity(r, pendingActions, null /* customIntent */);}
最后调用到ActivityThread
三、 Activity实例化过程
ActivityThread.java
/*** Extended implementation of activity launch. Used when server requests a launch or relaunch.*/Overridepublic Activity handleLaunchActivity(ActivityClientRecord r,PendingTransactionActions pendingActions, Intent customIntent) {final Activity a performLaunchActivity(r, customIntent);return a;}Activity实例化过程/** Core implementation of activity launch. */private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {Activity activity null;try {// 通过ClassLoader去加载需要启动的activity 反射实例化Activity对象java.lang.ClassLoader cl appContext.getClassLoader();activity mInstrumentation.newActivity(cl, component.getClassName(), r.intent);} catch (Exception e) {}// 在该方法内部创建window并设置window回调activity.attach(appContext, this, getInstrumentation() ...);theme//当实例化Activity对象后继续执行callActivityOnCreate 继而调用Activity的onCreate// 这样就完成了Activity生命周期的第一个回调onCreate方法if (r.isPersistable()) {mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);} else {mInstrumentation.callActivityOnCreate(activity, r.state);}}下面的代码比较简单就不贴了 frameworks/base/core/java/android/app/Instrumentation.java 四、 setContentView
这里内容太多我们另外写一篇文章。
五、 后续生命周期
接下来就是执行 Activity 其他生命周期函数 ActivityThread.java Overridepublic void handleStartActivity(ActivityClientRecord r,PendingTransactionActions pendingActions) {final Activity activity r.activity;// Restore instance stateif (pendingActions.shouldRestoreInstanceState()) {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);}}// Call postOnCreate()if (pendingActions.shouldCallOnPostCreate()) {activity.mCalled false;if (r.isPersistable()) {mInstrumentation.callActivityOnPostCreate(activity, r.state,r.persistentState);} else {mInstrumentation.callActivityOnPostCreate(activity, r.state);}}}Overridepublic void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,String reason) {}写在最后 在应用进程创建 activity 后activity 将执行以下操作
初始化值。调用构造函数。根据 activity 的当前生命周期状态相应地调用回调方法如 Activity.onCreate()。 通常onCreate() 方法对加载时间的影响最大因为它执行工作的开销最高加载和渲染视图以及初始化运行 activity 所需的对象。
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