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今天简单讲解一下PackageInstaller
文件路径：
packages/apps/PackageInstaller
frameworks/base/core/java/android/content/pm&res
下面开始讲解：
首先，我们说一下安装apk的几种方式，整体上可以分为2类，一类是有界面安装，一类是无界面安装。无界面安装分为内置apk开机安装和命令安装，命令安装又分为两类，一类电脑安装也就是adb命令，另一类是手机安装也就是pm命令。今天我们主要介绍有界面安装。
当然，我们从这个安装界面说起，这个界面是那个呢？就是PackageInstallerActivity这个acitvity。它是如何启动起来的呢？我们去看看它在AndroidManifest是如何定义的
<activity android:name=".PackageInstallerActivity"android:configChanges="orientation|keyboardHidden|screenSize"android:excludeFromRecents="true"android:screenOrientation="unspecified"><intent-filter><action android:name="android.intent.action.VIEW" /><action android:name="android.intent.action.INSTALL_PACKAGE" /><category android:name="android.intent.category.DEFAULT" /><data android:scheme="content" /><data android:scheme="file" /><data android:mimeType="application/vnd.android.package-archive" /></intent-filter><intent-filter><action android:name="android.intent.action.INSTALL_PACKAGE" /><category android:name="android.intent.category.DEFAULT" /><data android:scheme="content" /><data android:scheme="file" /></intent-filter></activity>很明显了，我们可以通过android.intent.action.INSTALL_PACKAGE这个action启动，也可以通过android.intent.action.VIEW这个action加上"application/vnd.android.package-archive"这个type启动，当然不加这个type也能启动，但是会找到很多这样的activity哦。另外，通过类名或包名启动也未尝不可的。所以，大部分启动是这样的
String apkFileString = Environment.getExternalStorageDirectory().getAbsolutePath()+"/.../packageName.pac";File apkFile = new File(apkFileString);Intent intent = new Intent(Intent.ACTION_VIEW);intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);intent.setDataAndType(Uri.fromFile(apkFile), "application/vnd.android.package-archive");mContext.startActivity(intent);这里我们传进去一个数据就是pakFile的Uri，然后我们去PackageInstallerActivity的onCreate中看看
final Intent intent = getIntent();mPackageURI = intent.getData();mPm = getPackageManager();mPkgInfo = PackageUtil.getPackageInfo(mPackageURI);获取到，我们刚才传进来的apkFile的Uri给了mPackageURI，接着获取到PackageManager，然后生成一个mPkgInfo也就是PackageParser.Package，这个很重要。我们看看PackageParser.Package是如何生成的，PackageParser.Package里面都包含了什么东西。那我们就要去PackageUtil.getPackageInfo中了
public static PackageParser.Package getPackageInfo(Uri packageURI) {final String archiveFilePath = packageURI.getPath();PackageParser packageParser = new PackageParser(archiveFilePath);File sourceFile = new File(archiveFilePath);DisplayMetrics metrics = new DisplayMetrics();metrics.setToDefaults();PackageParser.Package pkg = packageParser.parsePackage(sourceFile,archiveFilePath, metrics, 0);// Nuke the parser reference.packageParser = null;return pkg;}生成一个Package解析器，通过这个解析器来获取到PackageParser.Package中需要的数据，生成一个PackageParser.Package。我们看看PackageParser.parsePackage是如何生成一个PackageParser.Package的，这里传进去四个参数，一个Source File，apk文件，一个apk路径，一个屏幕信息，最后一个0，具体做什么的，进去之后就能明白了
public Package parsePackage(File sourceFile, String destCodePath,DisplayMetrics metrics, int flags) {mParseError = PackageManager.INSTALL_SUCCEEDED;mArchiveSourcePath = sourceFile.getPath();if (!sourceFile.isFile()) {Slog.w(TAG, "Skipping dir: " + mArchiveSourcePath);mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;return null;}if (!isPackageFilename(sourceFile.getName())&& (flags&PARSE_MUST_BE_APK) != 0) {if ((flags&PARSE_IS_SYSTEM) == 0) {// We expect to have non-.apk files in the system dir,// so don't warn about them.Slog.w(TAG, "Skipping non-package file: " + mArchiveSourcePath);}mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;return null;}if (DEBUG_JAR)Slog.d(TAG, "Scanning package: " + mArchiveSourcePath);XmlResourceParser parser = null;AssetManager assmgr = null;Resources res = null;boolean assetError = true;try {assmgr = new AssetManager();int cookie = assmgr.addAssetPath(mArchiveSourcePath);if (cookie != 0) {res = new Resources(assmgr, metrics, null);assmgr.setConfiguration(0, 0, null, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,Build.VERSION.RESOURCES_SDK_INT);parser = assmgr.openXmlResourceParser(cookie, ANDROID_MANIFEST_FILENAME);assetError = false;} else {Slog.w(TAG, "Failed adding asset path:"+mArchiveSourcePath);}} catch (Exception e) {Slog.w(TAG, "Unable to read AndroidManifest.xml of "+ mArchiveSourcePath, e);}if (assetError) {if (assmgr != null) assmgr.close();mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_MANIFEST;return null;}String[] errorText = new String[1];Package pkg = null;Exception errorException = null;try {// XXXX todo: need to figure out correct configuration.pkg = parsePackage(res, parser, flags, errorText);} catch (Exception e) {errorException = e;mParseError = PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;}if (pkg == null) {// If we are only parsing core apps, then a null with INSTALL_SUCCEEDED// just means to skip this app so don't make a fuss about it.if (!mOnlyCoreApps || mParseError != PackageManager.INSTALL_SUCCEEDED) {if (errorException != null) {Slog.w(TAG, mArchiveSourcePath, errorException);} else {Slog.w(TAG, mArchiveSourcePath + " (at "+ parser.getPositionDescription()+ "): " + errorText[0]);}if (mParseError == PackageManager.INSTALL_SUCCEEDED) {mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;}}parser.close();assmgr.close();return null;}parser.close();assmgr.close();// Set code and resource pathspkg.mPath = destCodePath;pkg.mScanPath = mArchiveSourcePath;//pkg.applicationInfo.sourceDir = destCodePath;//pkg.applicationInfo.publicSourceDir = destRes;pkg.mSignatures = null;return pkg;}首先sourceFile.isFile()判断一下是不是文件，如果不是，返回；接着isPackageFilename(sourceFile.getName())判断是不是apk文件，如果不是，返回；接着去获取三个关键变量，也就是
XmlResourceParser parser = null;AssetManager assmgr = null;Resources res = null;这三个是什么呢？这里简单说一下，AssetManager资产管理器，用来管理包中获取到的资源
assmgr = new AssetManager();int cookie = assmgr.addAssetPath(mArchiveSourcePath);通过addAssetPath可以获取到唯一标识该apk包资产的关键字cookie，也就是通过cookie可以找到该包的资源信息。Resources就是资源了，包括图片，color，xml等资源
res = new Resources(assmgr, metrics, null);parser = assmgr.openXmlResourceParser(cookie, ANDROID_MANIFEST_FILENAME);ANDROID_MANIFEST_FILENAME也就是
private static final String ANDROID_MANIFEST_FILENAME = "AndroidManifest.xml";这样就很明显了，这里生成的xml文件资源解析器是用来解析AndroidManifest文件的了。接下来就是关键了
String[] errorText = new String[1];Package pkg = null;Exception errorException = null;try {// XXXX todo: need to figure out correct configuration.pkg = parsePackage(res, parser, flags, errorText);} catch (Exception e) {errorException = e;mParseError = PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;}这里才是我们Package真正生成的地方了，也就是pkg = parsePackage(res, parser, flags, errorText)了。parsePackage是同构函数，一个是以File为首个参数，就是我们现在分析的这个，一个是以Resources为首个参数，就是我们接下来要讲的了，由于这个函数比较大，所以不再全部列出，只选取主要的
String pkgName = parsePackageName(parser, attrs, flags, outError);获取包名。
final Package pkg = new Package(pkgName);boolean foundApp = false;TypedArray sa = res.obtainAttributes(attrs,com.android.internal.R.styleabl