Android包管理机制（二）PackageInstaller安装APK
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
@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。
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。