Android 11.0 PackageManagerService（三）APK的安装过程

一. APK的安装步骤

安装步骤一：把APK的信息通过IO流的形式写入到PackageInstaller.Session中

安装步骤二：调用PackageInstaller.Session的commit方法，把APK的信息交给PackageManagerService处理

安装步骤三：进行Apk的Copy操作，进行安装

二. 点击安装后到完成APK的拷贝流程如下：

点击一个未安装的apk后，会弹出安装界面，点击确定按钮后，会进入PacakageInstallerActivity.java的bindUI()中的mAlert点击事件，点击apk后，弹出的安装界面底部显示的是一个Dialog，主要由bindUi构成，上面有取消和安装两个按钮，点击安装之后调用startInstall()进行安装。bingUi方法的代码如下：

private void bindUi() {
        mAlert.setIcon(mAppSnippet.icon);
        mAlert.setTitle(mAppSnippet.label);
        mAlert.setView(R.layout.install_content_view);
        mAlert.setButton(DialogInterface.BUTTON_POSITIVE, getString(R.string.install),
                (ignored, ignored2) -> {
                    if (mOk.isEnabled()) {
                        if (mSessionId != -1) {
                            mInstaller.setPermissionsResult(mSessionId, true);
                            finish();
                        } else {
                            // 进行APK的安装
                            startInstall();
                        }
                    }
                }, null);
        mAlert.setButton(DialogInterface.BUTTON_NEGATIVE, getString(R.string.cancel),
                (ignored, ignored2) -> {
                    // Cancel and finish
                    setResult(RESULT_CANCELED);
                    if (mSessionId != -1) {
                        // 如果mSessionId存在，执行setPermissionResult()完成取消安装
                        mInstaller.setPermissionsResult(mSessionId, false);
                    }
                    finish();
                }, null);
        setupAlert();

        mOk = mAlert.getButton(DialogInterface.BUTTON_POSITIVE);
        mOk.setEnabled(false);

        if (!mOk.isInTouchMode()) {
            mAlert.getButton(DialogInterface.BUTTON_NEGATIVE).requestFocus();
        }
}

startInstall方法组装了一个Intent，并跳转到 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。

private void startInstall() {
        // Start subactivity to actually install the application
        Intent newIntent = new Intent();
        newIntent.putExtra(PackageUtil.INTENT_ATTR_APPLICATION_INFO,
                mPkgInfo.applicationInfo);
        newIntent.setData(mPackageURI);
        // 设置Intent中的class为InstallInstalling，用来进行Activity跳转
        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 (mReferrerURI != null) {
            newIntent.putExtra(Intent.EXTRA_REFERRER, mReferrerURI);
        }
        if (mOriginatingUid != PackageInstaller.SessionParams.UID_UNKNOWN) {
            newIntent.putExtra(Intent.EXTRA_ORIGINATING_UID, mOriginatingUid);
        }
        if (installerPackageName != null) {
            newIntent.putExtra(Intent.EXTRA_INSTALLER_PACKAGE_NAME,
                    installerPackageName);
        }
        if (getIntent().getBooleanExtra(Intent.EXTRA_RETURN_RESULT, false)) {
            newIntent.putExtra(Intent.EXTRA_RETURN_RESULT, true);
        }
        newIntent.addFlags(Intent.FLAG_ACTIVITY_FORWARD_RESULT);
        if(localLOGV) Log.i(TAG, "downloaded app uri="+mPackageURI);
        startActivity(newIntent);
        finish();
    }

InstallInstalling 的Activity启动后，进入onCreate方法

主要分为6步：

1. 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

2. 根据mInstallId向InstallEventReceiver注册一个观察者，launchFinishBasedOnResult会接收到安装事件的回调，无论安装成功或者是安装失败都会关闭当前的Activity(InstallInstalling)。如果saveInstanceState为null，代码的逻辑也是类似的。

3.  创建SessionParams，它用来代表安装会话的参数，组装Params

4. 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

5. 向InstallEventReceiver注册一个观察者返回一个新的mInstallId

6. PackageInstaller的createSession方法内部会通过IPackageInstallerService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

@Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        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.AppSnippet as = PackageUtil.getAppSnippet(this, appInfo, sourceFile);

            mAlert.setIcon(as.icon);
            mAlert.setTitle(as.label);
            mAlert.setView(R.layout.install_content_view);
            mAlert.setButton(DialogInterface.BUTTON_NEGATIVE, getString(R.string.cancel),
                    (ignored, ignored2) -> {
                        if (mInstallingTask != null) {
                            mInstallingTask.cancel(true);
                        }

                        if (mSessionId > 0) {
                            getPackageManager().getPackageInstaller().abandonSession(mSessionId);
                            mSessionId = 0;
                        }

                        setResult(RESULT_CANCELED);
                        finish();
                    }, null);
            setupAlert();
            requireViewById(R.id.installing).setVisibility(View.VISIBLE);
            // 1. 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是等待安装的事件Id
            if (savedInstanceState != null) {
                mSessionId = savedInstanceState.getInt(SESSION_ID);
                mInstallId = savedInstanceState.getInt(INSTALL_ID);

                // Reregister for result; might instantly call back if result was delivered while
                // activity was destroyed
                try {
                    // 2. 根据mInstallId向InstallEventReceiver注册一个观察者，           
                    // launchFinishBasedOnResult会接收到安装事件的回调，无论安装成功还是失败
                    // 都会关闭当前的Activity(InstallInstalling)。如果savedInstanceState为          
                    // null，代码的逻辑也是类似的
                    InstallEventReceiver.addObserver(this, mInstallId,
                            this::launchFinishBasedOnResult);
                } catch (EventResultPersister.OutOfIdsException e) {
                    // Does not happen
                }
            } else {
                //3. 创建SessionParams，它用来代表安装会话的参数，组装params
                PackageInstaller.SessionParams params = new PackageInstaller.SessionParams(
                        PackageInstaller.SessionParams.MODE_FULL_INSTALL);
                params.setInstallAsInstantApp(false);
                params.setReferrerUri(getIntent().getParcelableExtra(Intent.EXTRA_REFERRER));
                params.setOriginatingUri(getIntent()
                        .getParcelableExtra(Intent.EXTRA_ORIGINATING_URI));
                params.setOriginatingUid(getIntent().getIntExtra(Intent.EXTRA_ORIGINATING_UID,
                        UID_UNKNOWN));
                params.setInstallerPackageName(getIntent().getStringExtra(
                        Intent.EXTRA_INSTALLER_PACKAGE_NAME));
                params.setInstallReason(PackageManager.INSTALL_REASON_USER);
                // 4. 根据mPackageUri对包进行轻量级的解析，并将解析的参数赋值给SessionParams
                File file = new File(mPackageURI.getPath());
                try {
                    PackageParser.PackageLite pkg = PackageParser.parsePackageLite(file, 0);
                    params.setAppPackageName(pkg.packageName);
                    params.setInstallLocation(pkg.installLocation);
                    params.setSize(
                            PackageHelper.calculateInstalledSize(pkg, false, params.abiOverride));
                } catch (PackageParser.PackageParserException e) {
                    Log.e(LOG_TAG, "Cannot parse package " + file + ". Assuming defaults.");