前言
在本系列上一篇文章Android包管理机制（一）PackageInstaller的初始化中我们学习了PackageInstaller是如何初始化的，这一篇文章我们接着学习PackageInstaller是如何安装APK的。本系列文章的源码基于Android8.0。
1.PackageInstaller中的处理
紧接着上一篇的内容，在PackageInstallerActivity调用startInstallConfirm方法初始化安装确认界面后，这个安装确认界面就会呈现给用户，用户如果想要安装这个应用程序就会点击确定按钮，就会调用PackageInstallerActivity的onClick方法，如下所示。
packages/apps/PackageInstaller/src/com/android/packageinstaller/PackageInstallerActivity.java
public void onClick(View v) { if (v == mOk) { if (mOk.isEnabled()) { if (mOkCanInstall || mScrollView == null) { if (mSessionId != -1) { mInstaller.setPermissionsResult(mSessionId, true); finish(); } else { startInstall();//1 } } else { mScrollView.pageScroll(View.FOCUS_DOWN); } } } else if (v == mCancel) { ... finish(); } } onClick方法中分别对确定和取消按钮做处理，主要查看对确定按钮的处理，注释1处调用了startInstall方法：
packages/apps/PackageInstaller/src/com/android/packageinstaller/PackageInstallerActivity.java private void startInstall() { Intent newIntent = new Intent(); newIntent.putExtra(PackageUtil.INTENT_ATTR_APPLICATION_INFO, mPkgInfo.applicationInfo); newIntent.setData(mPackageURI);//1 newIntent.setClass(this, InstallInstalling.class); String installerPackageName = getIntent().getStringExtra( Intent.EXTRA_INSTALLER_PACKAGE_NAME); if (mOriginatingURI != null) { newIntent.putExtra(Intent.EXTRA_ORIGINATING_URI, mOriginatingURI); } ... if(localLOGV) Log.i(TAG, "downloaded app uri="+mPackageURI); startActivity(newIntent); finish(); } startInstall方法用于跳转到InstallInstalling这个Activity，并关闭掉当前的PackageInstallerActivity。InstallInstalling主要用于向包管理器发送包的信息并处理包管理的回调。 InstallInstalling的onCreate方法如下所示。
packages/apps/PackageInstaller/src/com/android/packageinstaller/InstallInstalling.java @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.install_installing); ApplicationInfo appInfo = getIntent() .getParcelableExtra(PackageUtil.INTENT_ATTR_APPLICATION_INFO); mPackageURI = getIntent().getData(); if ("package".equals(mPackageURI.getScheme())) { try { getPackageManager().installExistingPackage(appInfo.packageName); launchSuccess(); } catch (PackageManager.NameNotFoundException e) { launchFailure(PackageManager.INSTALL_FAILED_INTERNAL_ERROR, null); } } else { //根据mPackageURI创建一个对应的File final File sourceFile = new File(mPackageURI.getPath()); PackageUtil.initSnippetForNewApp(this, PackageUtil.getAppSnippet(this, appInfo, sourceFile), R.id.app_snippet); //如果savedInstanceState不为null，获取此前保存的mSessionId和mInstallId if (savedInstanceState != null) { //1 mSessionId = savedInstanceState.getInt(SESSION_ID); mInstallId = savedInstanceState.getInt(INSTALL_ID); //向InstallEventReceiver注册一个观察者 try { InstallEventReceiver.addObserver(this, mInstallId, this::launchFinishBasedOnResult);//2 } catch (EventResultPersister.OutOfIdsException e) { } } else { PackageInstaller.SessionParams params = new PackageInstaller.SessionParams( PackageInstaller.SessionParams.MODE_FULL_INSTALL);//3 params.referrerUri = getIntent().getParcelableExtra(Intent.EXTRA_REFERRER); params.originatingUri = getIntent() .getParcelableExtra(Intent.EXTRA_ORIGINATING_URI); params.originatingUid = getIntent().getIntExtra(Intent.EXTRA_ORIGINATING_UID, UID_UNKNOWN); File file = new File(mPackageURI.getPath());//4 try { PackageParser.PackageLite pkg = PackageParser.parsePackageLite(file, 0);//5 params.setAppPackageName(pkg.packageName); params.setInstallLocation(pkg.installLocation); params.setSize( PackageHelper.calculateInstalledSize(pkg, false, params.abiOverride)); } catch (PackageParser.PackageParserException e) { ... } try { mInstallId = InstallEventReceiver .addObserver(this, EventResultPersister.GENERATE_NEW_ID, this::launchFinishBasedOnResult);//6 } catch (EventResultPersister.OutOfIdsException e) { launchFailure(PackageManager.INSTALL_FAILED_INTERNAL_ERROR, null); } try { mSessionId = getPackageManager().getPackageInstaller().createSession(params);//7 } catch (IOException e) { launchFailure(PackageManager.INSTALL_FAILED_INTERNAL_ERROR, null); } } ... mSessionCallback = new InstallSessionCallback(); } } onCreate方法中会分别对package和content协议的Uri进行处理，我们来看content协议的Uri处理部分。注释1处如果savedInstanceState不为null，获取此前保存的mSessionId和mInstallId，其中mSessionId是安装包的会话id，mInstallId是等待的安装事件id。注释2处根据mInstallId向InstallEventReceiver注册一个观察者，launchFinishBasedOnResult会接收到安装事件的回调，无论安装成功或者失败都会关闭当前的Activity(InstallInstalling)。如果savedInstanceState为null，代码的逻辑也是类似的，注释3处创建SessionParams，它用来代表安装会话的参数，注释4、5处根据mPackageUri对包（APK）进行轻量级的解析，并将解析的参数赋值给SessionParams。注释6处和注释2处类似向InstallEventReceiver注册一个观察者返回一个新的mInstallId，其中InstallEventReceiver继承自BroadcastReceiver，用于接收安装事件并回调给EventResultPersister。 注释7处PackageInstaller的createSession方法内部会通过IPackageInstaller与PackageInstallerService进行进程间通信，最终调用的是PackageInstallerService的createSession方法来创建并返回mSessionId。
InstallInstalling的onCreate方法就分析到这，接着查看InstallInstalling的onResume方法：packages/apps/PackageInstaller/src/com/android/packageinstaller/InstallInstalling.java @Override protected void onResume() { super.onResume(); if (mInstallingTask == null) { PackageInstaller installer = getPackageManager().getPackageInstaller(); PackageInstaller.SessionInfo sessionInfo = installer.getSessionInfo(mSessionId);//1 if (sessionInfo != null && !sessionInfo.isActive()) { //2 mInstallingTask = new InstallingAsyncTask(); mInstallingTask.execute(); } else { mCancelButton.setEnabled(false); setFinishOnTouchOutside(false); } } } 注释1处根据mSessionId得到SessionInfo，SessionInfo代表安装会话的详细信息。注释2处如果sessionInfo不为Null并且不是活动的，就创建并执行InstallingAsyncTask。InstallingAsyncTask的doInBackground方法中会根据包(APK)的Uri，将APK的信息通过IO流的形式写入到PackageInstaller.Session中。InstallingAsyncTask的onPostExecute方法如下所示。
packages/apps/PackageInstaller/src/com/android/packageinstaller/InstallInstalling.java @Override protected void onPostExecute(PackageInstaller.Session session) { if (session != null) { Intent broadcastIntent = new Intent(BROADCAST_ACTION); broadcastIntent.setPackage( getPackageManager().getPermissionControllerPackageName()); broadcastIntent.putExtra(EventResultPersister.EXTRA_ID, mInstallId); PendingIntent pendingIntent = PendingIntent.getBroadcast( InstallInstalling.this, mInstallId, broadcastIntent, PendingIntent.FLAG_UPDATE_CURRENT); session.commit(pendingIntent.getIntentSender());//1 mCancelButton.setEnabled(false); setFinishOnTouchOutside(false); } else { getPackageManager().getPackageInstaller().abandonSession(mSessionId); if (!isCancelled()) { launchFailure(PackageManager.INSTALL_FAILED_INVALID_APK, null); } } } 创建了一个PendingIntent，并将该PendingIntent的IntentSender通过注释1处的PackageInstaller.Session的commit方法发送出去，发送去哪了呢？接着查看PackageInstaller.Session的commit方法。
frameworks/base/core/java/android/content/pm/PackageInstaller.java public void commit(@NonNull IntentSender statusReceiver) { try { mSession.commit(statusReceiver); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); }} mSession的类型为IPackageInstallerSession，这说明要通过IPackageInstallerSession来进行进程间的通信，最终会调用PackageInstallerSession的commit方法，这样代码逻辑就到了Java框架层的。
2.Java框架层的处理
frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java
@Overridepublic void commit(IntentSender statusReceiver) { Preconditions.checkNotNull(statusReceiver); ... mActiveCount.incrementAndGet(); final PackageInstallObserverAdapter adapter = new PackageInstallObserverAdapter(mContext, statusReceiver, sessionId, mIsInstallerDeviceOwner, userId); mHandler.obtainMessage(MSG_COMMIT, adapter.getBinder()).sendToTarget();//1} commit方法中会将包的信息封装为PackageInstallObserverAdapter ，它在PMS中被定义。在注释1处会向Handler发送一个类型为MSG_COMMIT的消息，其中adapter.getBinder()会得到IPackageInstallObserver2.Stub类型的观察者，从类型就知道这个观察者是可以跨进程进行回调的。处理该消息的代码如下所示。
private final Handler.Callback mHandlerCallback = new Handler.Callback() { @Override public boolean handleMessage(Message msg) { final PackageInfo pkgInfo = mPm.getPackageInfo( params.appPackageName, PackageManager.GET_SIGNATURES | PackageManager.MATCH_STATIC_SHARED_LIBRARIES /*flags*/, userId); final ApplicationInfo appInfo = mPm.getApplicationInfo( params.appPackageName, 0, userId); synchronized (mLock) { if (msg.obj != null) { mRemoteObserver = (IPackageInstallObserver2) msg.obj;//1 } try { commitLocked(pkgInfo, appInfo);//2 } catch (PackageManagerException e) { final String completeMsg = ExceptionUtils.getCompleteMessage(e); Slog.e(TAG, "Commit of session " + sessionId + " failed: " + completeMsg); destroyInternal(); dispatchSessionFinished(e.error, completeMsg, null);//3 } return true; } } }; 注释1处获取IPackageInstallObserver2类型的观察者mRemoteObserver，注释2处的commitLocked方法如下所示。
frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java private void commitLocked(PackageInfo pkgInfo, ApplicationInfo appInfo) throws PackageManagerException { ... mPm.installStage(mPackageName, stageDir, stageCid, localObserver, params, installerPackageName, installerUid, user, mCertificates); } commitLocked方法比较长，这里截取最主要的信息，会调用PMS的installStage方法，这样代码逻辑就进入了PMS中。
回到mHandlerCallback的handleMessage方法，如果commitLocked方法出现PackageManagerException异常，就会调用注释3处的dispatchSessionFinished方法，它的实现如下所示：frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java private void dispatchSessionFinished(int returnCode, String msg, Bundle extras) { mFinalStatus = returnCode; mFinalMessage = msg; if (mRemoteObserver != null) { try { mRemoteObserver.onPackageInstalled(mPackageName, returnCode, msg, extras);//1 } catch (RemoteException ignored) { } } ... } 注释1处会调用IPackageInstallObserver2的onPackageInstalled方法，具体是实现在PackageInstallObserver类中：
frameworks/base/core/java/android/app/PackageInstallObserver.java public class PackageInstallObserver { private final IPackageInstallObserver2.Stub mBinder = new IPackageInstallObserver2.Stub() { ... @Override public void onPackageInstalled(String basePackageName, int returnCode, String msg, Bundle extras) { PackageInstallObserver.this.onPackageInstalled(basePackageName, returnCode, msg, extras);//1 } }; 注释1处调用了PackageInstallObserver的onPackageInstalled方法，实现这个方法的类为PackageInstallObserver的子类、前面提到的PackageInstallObserverAdapter。总结一下就是dispatchSessionFinished方法会通过mRemoteObserver的onPackageInstalled方法，将Complete方法出现的PackageManagerException的异常信息回调给PackageInstallObserverAdapter。
3.总结
本篇文章讲解了PackageInstaller安装APK的过程，简单来说就两步：
- 将APK的信息通过IO流的形式写入到PackageInstaller.Session中。
- 调用PackageInstaller.Session的commit方法，将APK的信息交由PMS处理。
由于PMS中对APK安装的处理比较复杂，因此关于PMS的处理部分会在本系列的下一篇文章进行讲解。