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於Android8.0。 1.PackageInsta ...

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於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後，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式就會點擊確定按鈕，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();
        }
    }

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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，註釋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();
 }

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startInstall方法用於跳轉到InstallInstalling這個Activity，並關閉掉當前的PackageInstallerActivity。InstallInstalling主要用於向包管理器發送包的信息並處理包管理的回調。 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註冊一個觀察者
             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();
     }
 }

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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。註釋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。註釋2處根據mInstallId向InstallEventReceiver註冊一個觀察者，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，註釋3處創建SessionParams，它用來代表安裝會話的參數，註釋4、5處根據mPackageUri對包（APK）進行輕量級的解析，並將解析的參數賦值給SessionParams。註釋6處和註釋2處類似向InstallEventReceiver註冊一個觀察者返回一個新的mInstallId，其中InstallEventReceiver繼承自BroadcastReceiver，用於接收安裝事件並回調給EventResultPersister。註釋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方法來創建並返回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);
         }
     }
 }

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註釋1處根據mSessionId得到SessionInfo，SessionInfo代表安裝會話的詳細信息。註釋2處如果sessionInfo不為Null並且不是活動的，就創建並執行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);
         }
     }
 }

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創建了一個PendingIntent，並將該PendingIntent的IntentSender通過註釋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();
           }
}

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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
}

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commit方法中會將包的信息封裝為PackageInstallObserverAdapter ，它在PMS中被定義。在註釋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;
          }
      }
  };

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註釋1處獲取IPackageInstallObserver2類型的觀察者mRemoteObserver，註釋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);
  }

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commitLocked方法比較長，這裡截取最主要的信息，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，就會調用註釋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) {
           }
       }
       ...
   }

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註釋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
        }
    };

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註釋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。

由於PMS中對APK安裝的處理比較複雜，因此關於PMS的處理部分會在本系列的下一篇文章進行講解。