Android包管理機制（二）PackageInstaller安裝APK
前言
在本系列上一篇文章Android包管理機制（一）PackageInstaller的初始化中我們學習了PackageInstaller是如何初始化的，這一篇文章我們接著學習PackageInstaller是如何安裝APK的。本系列文章的源碼基于Android8.0。
1.PackageInstaller中的處理
緊接著上一篇的內容，在PackageInstallerActivity調用startInstallConfirm方法初始化安裝確認界面后，這個安裝確認界面就會呈現給用戶，用戶如果想要安裝這個應用程序就會點擊確定按鈕，就會調用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方法中分別對確定和取消按鈕做處理，主要查看對確定按鈕的處理，注釋1處調用了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方法用于跳轉到InstallInstalling這個Activity，并關閉掉當前的PackageInstallerActivity。InstallInstalling主要用于向包管理器發送包的信息并處理包管理的回調。 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 { //根據mPackageURI創建一個對應的File final File sourceFile = new File(mPackageURI.getPath()); PackageUtil.initSnippetForNewApp(this, PackageUtil.getAppSnippet(this, appInfo, sourceFile), R.id.app_snippet); //如果savedInstanceState不為null，獲取此前保存的mSessionId和mInstallId if (savedInstanceState != null) {//1 mSessionId = savedInstanceState.getInt(SESSION_ID); mInstallId = savedInstanceState.getInt(INSTALL_ID); //向InstallEventReceiver注冊一個觀察者 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方法中會分別對package和content協議的Uri進行處理，我們來看content協議的Uri處理部分。注釋1處如果savedInstanceState不為null，獲取此前保存的mSessionId和mInstallId，其中mSessionId是安裝包的會話id，mInstallId是等待的安裝事件id。注釋2處根據mInstallId向InstallEventReceiver注冊一個觀察者，launchFinishBasedOnResult會接收到安裝事件的回調，無論安裝成功或者失敗都會關閉當前的Activity(InstallInstalling)。如果savedInstanceState為null，代碼的邏輯也是類似的，注釋3處創建SessionParams，它用來代表安裝會話的參數，注釋4、5處根據mPackageUri對包（APK）進行輕量級的解析，并將解析的參數賦值給SessionParams。注釋6處和注釋2處類似向InstallEventReceiver注冊一個觀察者返回一個新的mInstallId，其中InstallEventReceiver繼承自BroadcastReceiver，用于接收安裝事件并回調給EventResultPersister。 注釋7處PackageInstaller的createSession方法內部會通過IPackageInstaller與PackageInstallerService進行進程間通信，最終調用的是PackageInstallerService的createSession方法來創建并返回mSessionId。
InstallInstalling的onCreate方法就分析到這，接著查看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); } } }
注釋1處根據mSessionId得到SessionInfo，SessionInfo代表安裝會話的詳細信息。注釋2處如果sessionInfo不為Null并且不是活動的，就創建并執行InstallingAsyncTask。InstallingAsyncTask的doInBackground方法中會根據包(APK)的Uri，將APK的信息通過IO流的形式寫入到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); } } }
創建了一個PendingIntent，并將該PendingIntent的IntentSender通過注釋1處的PackageInstaller.Session的commit方法發送出去，發送去哪了呢？接著查看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的類型為IPackageInstallerSession，這說明要通過IPackageInstallerSession來進行進程間的通信，最終會調用PackageInstallerSession的commit方法，這樣代碼邏輯就到了Java框架層的。
2.Java框架層的處理
frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java
@Override public 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方法中會將包的信息封裝為PackageInstallObserverAdapter ，它在PMS中被定義。在注釋1處會向Handler發送一個類型為MSG_COMMIT的消息，其中adapter.getBinder()會得到IPackageInstallObserver2.Stub類型的觀察者，從類型就知道這個觀察者是可以跨進程進行回調的。處理該消息的代碼如下所示。
frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java
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; } } };
注釋1處獲取IPackageInstallObserver2類型的觀察者mRemoteObserver，注釋2處的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方法比較長，這里截取最主要的信息，會調用PMS的installStage方法，這樣代碼邏輯就進入了PMS中。
回到mHandlerCallback的handleMessage方法，如果commitLocked方法出現PackageManagerException異常，就會調用注釋3處的dispatchSessionFinished方法，它的實現如下所示：
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) { } } ... }
注釋1處會調用IPackageInstallObserver2的onPackageInstalled方法，具體是實現在PackageInstallObserver類中：
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 } };
注釋1處調用了PackageInstallObserver的onPackageInstalled方法，實現這個方法的類為PackageInstallObserver的子類、前面提到的PackageInstallObserverAdapter。總結一下就是dispatchSessionFinished方法會通過mRemoteObserver的onPackageInstalled方法，將Complete方法出現的PackageManagerException的異常信息回調給PackageInstallObserverAdapter。
3.總結
本篇文章講解了PackageInstaller安裝APK的過程，簡單來說就兩步：
- 將APK的信息通過IO流的形式寫入到PackageInstaller.Session中。
- 調用PackageInstaller.Session的commit方法，將APK的信息交由PMS處理。
由于PMS中對APK安裝的處理比較復雜，因此關于PMS的處理部分會在本系列的下一篇文章進行講解。
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