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《android framework常用api源码分析》android生态在中国已经发展非常庞大了，一方面是因为手机移动端的覆盖，另一方面是从事android开发的人也月来越多。那么用人单位对android要求也变了，对android不仅要熟练使用而且要懂得原理。而就程序员自身阅读源码有什么那些？这里我通过自己理解归纳了一下。
提高程序执行效率，正确理解api可以高效使用，优化内存和执行效率。
避免八阿哥强势逆袭，android开发同学都知道android找bug比较麻烦，尤其是一下jni底层调用错误信息不够明确地方更加难找。
帮助自己写出优雅的代码，开发需要规范，而源码中有很多优秀的谷歌规范。
优秀的设计模式，帮助自己提升程序造诣。
黑科技，通过反射高一些api不能够达到的功能，例如插件化、热更新。
上面是简单个人理解，有更多补充欢迎留言。所以这里准备出一个系列的文章来分析android framework api， 这些文章也是来自整理于网络，所以要感谢那些具有分享精神的大神们。
文章目录：
- apk 打包过程解析。
- handler 消息机制。
- AsyncTask 异步任务。
- HandlerThread handler线程。
- IntentService意图服务。
- Zygote进程。
- SystemServer进程。
- Launcher 程序。
- app 进程启动流程。
- 系统app启动安装流程。
- app应用安装流程。
- Activity启动流程。
- LruCache内存缓存
如果是从事系统rom工作的同学这篇文章都不用看了，但是如果app应用开发的同学想了解一下系统app是如何安装就可以通过这篇文章了解一下；首先系统app也是普通app只是放置的目录是不一样，是系统预留好的，只要手机启动就可以扫描重新安装，能够在这个目录操作要么是做系统rom时候加入进去，要么就是获取超级用户su的权限，那么就可以把自己app放入系统apk目录做成系统app。
大家应该都知道，Android系统启动之后，我们就可以在一个应用中打开另一个从未打开过的应用，或者是在一个应用中发送广播，如果另外一个应用设置了这个广播的接收器，那么这个应用进程就会被启动并接收该广播并作出相应的处理，这样的例子很多，我们可以猜测到Android系统在启动的时候就会抓取到了系统中所有安装的应用信息（应该是解析apk文件的Manifest信息），即在Android系统的启动过程中就已经解析了系统中安装应用的androidManifest.xml文件并保存起来了，那么这个过程具体是如何的呢?
其实android系统启动过程中解析Manifest的流程是通过PackageManagerService服务来实现的。这里我们重点分析一下PackageManagerService服务是如何解析Manifest的。
首先看一下在SystemServer进程启动过程中是如何启动PackageManagerService服务的：
private void startBootstrapServices() {
...
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
...
}在SystemServer进程启动过程中会调用SystemServer类的startBootstrapServices方法（主要用于启动ActivityManagerService服务和PackageManagerService服务），然后会在这个方法中会调用PackageManagerService.main静态方法，这个方法主要是用来初始化PackageManagerService服务并执行相关逻辑的。下面我来看一下main方法的具体逻辑：
public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
ServiceManager.addService("package", m);
return m;
}可以发现main方法的实现逻辑主要是创建了一个PackageManagerService对象，并将这个对象添加到ServierManager中为其他组件提供服务。好吧，看来PackageManagerService的初始化操作主要是在PackageManagerService的构造方法中了，下面我们来看一下其构造方法的实现逻辑：
File dataDir = Environment.getDataDirectory();
mAppDataDir = new File(dataDir, "data");
mAppInstallDir = new File(dataDir, "app");
mAppLib32InstallDir = new File(dataDir, "app-lib");
mAsecInternalPath = new File(dataDir, "app-asec").getPath();
mUserAppDataDir = new File(dataDir, "user");
mDrmAppPrivateInstallDir = new File(dataDir, "app-private");PackageManagerService的构造方法代码量比较大，这里就不贴出所有的代码了，我们主要和解析Manifest相关的主要代码，在构造方法中有这样几段代码。可以发现在构造方法中，解析了系统中几个apk的安装目录，这几个目录就是系统中安装apk的目录，android系统会默认解析这几个目录下apk文件，也就是说如果我们android手机在其他的目录下存在apk文件系统是不会默认解析的，反过来说，如果我们把我们的apk文件移动到这几个目录下，那么重新启动操作系统，该apk文件就会被系统解析并执行相关的逻辑操作，具体做什么操作呢？我们看下面的实现。
/ overlay packages if they reside in VENDOR_OVERLAY_DIR.
File vendorOverlayDir = new File(VENDOR_OVERLAY_DIR);
scanDirLI(vendorOverlayDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags | SCAN_TRUSTED_OVERLAY, 0);
// Find base frameworks (resource packages without code).
scanDirLI(frameworkDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR
| PackageParser.PARSE_IS_PRIVILEGED,
scanFlags | SCAN_NO_DEX, 0);
// Collected privileged system packages.
final File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
scanDirLI(privilegedAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR
| PackageParser.PARSE_IS_PRIVILEGED, scanFlags, 0);
// Collect ordinary system packages.
final File systemAppDir = new File(Environment.getRootDirectory(), "app");
scanDirLI(systemAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);
// Collect all vendor packages.
File vendorAppDir = new File("/vendor/app");
try {
vendorAppDir = vendorAppDir.getCanonicalFile();
} catch (IOException e) {
// failed to look up canonical path, continue with original one
}
scanDirLI(vendorAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);
// Collect all OEM packages.
final File oemAppDir = new File(Environment.getOemDirectory(), "app");
scanDirLI(oemAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);在我们刚刚的PackageManagerService.mani方法中，解析完刚刚的几个系统目录之后系统会调用scanDirLI方法，那么这个方法主要是做什么用的呢？看它的名字应该是遍历这个系统目录。好吧，这个方法主要就是用于解析上面几个目录下的apk文件的。不信？我们看一下scanDirLI方法的具体实现：
private void scanDirLI(File dir, int parseFlags, int scanFlags, long currentTime) {
final File[] files = dir.listFiles();
if (ArrayUtils.isEmpty(files)) {
Log.d(TAG, "No files in app dir " + dir);
return;
}
if (DEBUG_PACKAGE_SCANNING) {
Log.d(TAG, "Scanning app dir " + dir + " scanFlags=" + scanFlags
+ " flags=0x" + Integer.toHexString(parseFlags));
}
for (File file : files) {
final boolean isPackage = (isApkFile(file) || file.isDirectory())
&& !PackageInstallerService.isStageName(file.getName());
if (!isPackage) {
// Ignore entries which are not packages
continue;
}
try {
scanPackageLI(file, parseFlags | PackageParser.PARSE_MUST_BE_APK,
scanFlags, currentTime, null);
} catch (PackageManagerException e) {
Slog.w(TAG, "Failed to parse " + file + ": " + e.getMessage());
// Delete invalid userdata apps
if ((parseFlags & PackageParser.PARSE_IS_SYSTEM) == 0 &&
e.error == PackageManager.INSTALL_FAILED_INVALID_APK) {
logCriticalInfo(Log.WARN, "Deleting invalid package at " + file);
if (file.isDirectory()) {
mInstaller.rmPackageDir(file.getAbsolutePath());
} else {
file.delete();
}
}
}
}
}可以放下其首先会遍历该目录下的所有文件，并判断是否是apk文件，如果是apk文件则调用scanPackageLI方法，scanPackageLI方法的名字很明显，就是用于解析这个apk文件的。
继续看一下scanPakcageLI方法的实现：
private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
long currentTime, UserHandle user) throws PackageManagerException {
if (DEBUG_INSTALL) Slog.d(TAG, "Parsing: " + scanFile);
parseFlags |= mDefParseFlags;
PackageParser pp = new PackageParser();
pp.setSeparateProcesses(mSeparateProcesses);
pp.setOnlyCoreApps(mOnlyCore);
pp.setDisplayMetrics(mMetrics);
if ((scanFlags & SCAN_TRUSTED_OVERLAY) != 0) {
parseFlags |= PackageParser.PARSE_TRUSTED_OVERLAY;
}
final PackageParser.Package pkg;
try {
pkg = pp.parsePackage(scanFile, parseFlags);
} catch (PackageParserException e) {
throw PackageManagerException.from(e);
}
...
}好吧，这个方法也比较复杂，这里只是列出重点相关的代码，我们可以发现在这个方法中创建了一个PackagerParser对象，并调用了parsePackage方法，这个方法其实就是解析Manifest的主要方法，我们可以看一下其具体的实现：
public Package parsePackage(File packageFile, int flags) throws PackageParserException {
if (packageFile.isDirectory()) {
return parseClusterPackage(packageFile, flags);
} else {
return parseMonolithicPackage(packageFile, flags);
}
}可以发现，若我们解析的File对象是一个文件夹则执行调用parseClusterPackage方法，否则调用执行parseMonolithicPackage方法，很明显的因为我们这里解析的是apk文件（在上一方法中我们循环遍历得到了apk文件，这里的File对象就代表了一个个的apk文件信息），所以这里会执行parseMonolithicPackage方法，然后我们来看一下parseMonolithicPackage方法：
public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {
if (mOnlyCoreApps) {
final PackageLite lite = parseMonolithicPackageLite(apkFile, flags);
if (!lite.coreApp) {
throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
"Not a coreApp: " + apkFile);
}
}
final AssetManager assets = new AssetManager();
try {
final Package pkg = parseBaseApk(apkFile, assets, flags);
pkg.codePath = apkFile.getAbsolutePath();
return pkg;
} finally {
IoUtils.closeQuietly(assets);
}
}可以看出，这里又调用了parseBaseApk方法：
private Package parseBaseApk(File apkFile, AssetManager assets, int flags)
...
final Package pkg = parseBaseApk(res, parser, flags, outError);
...
}可以看出，这个parseBaseApk方法调用了其重载的parseBaseApk方法：
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("application")) {
if (foundApp) {
if (RIGID_PARSER) {
outError[0] = "<manifest> has more than one <application>";
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
} else {
Slog.w(TAG, "<manifest> has more than one <application>");
XmlUtils.skipCurrentTag(parser);
continue;
}
}
foundApp = true;
if (!parseBaseApplication(pkg, res, parser, attrs, flags, outError)) {
return null;
}
} else if (tagName.equals("overlay")) {
pkg.mTrustedOverlay = trustedOverlay;
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestResourceOverlay);
pkg.mOverlayTarget = sa.getString(
com.android.internal.R.styleable.AndroidManifestResourceOverlay_targetPackage);
pkg.mOverlayPriority = sa.getInt(
com.android.internal.R.styleable.AndroidManifestResourceOverlay_priority,
-1);
sa.recycle();
if (pkg.mOverlayTarget == null) {
outError[0] = "<overlay> does not specify a target package";
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
}
if (pkg.mOverlayPriority < 0 || pkg.mOverlayPriority > 9999) {
outError[0] = "<overlay> priority must be between 0 and 9999";
mParseError =
PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("key-sets")) {
if (!parseKeySets(pkg, res, parser, attrs, outError)) {
return null;
}
} else if (tagName.equals("permission-group")) {
if (parsePermissionGroup(pkg, flags, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("permission")) {
if (parsePermission(pkg, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("permission-tree")) {
if (parsePermissionTree(pkg, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("uses-permission")) {
if (!parseUsesPermission(pkg, res, parser, attrs)) {
return null;
}
} else if (tagName.equals("uses-permission-sdk-m")
|| tagName.equals("uses-permission-sdk-23")) {
if (!parseUsesPermission(pkg, res, parser, attrs)) {
return null;
}
} else if (tagName.equals("uses-configuration")) {
ConfigurationInfo cPref = new ConfigurationInfo();
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesConfiguration);
cPref.reqTouchScreen = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqTouchScreen,
Configuration.TOUCHSCREEN_UNDEFINED);
cPref.reqKeyboardType = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqKeyboardType,
Configuration.KEYBOARD_UNDEFINED);
if (sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqHardKeyboard,
false)) {
cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_HARD_KEYBOARD;
}
cPref.reqNavigation = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqNavigation,
Configuration.NAVIGATION_UNDEFINED);
if (sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqFiveWayNav,
false)) {
cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_FIVE_WAY_NAV;
}
sa.recycle();
pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("uses-feature")) {
FeatureInfo fi = parseUsesFeature(res, attrs);
pkg.reqFeatures = ArrayUtils.add(pkg.reqFeatures, fi);
if (fi.name == null) {
ConfigurationInfo cPref = new ConfigurationInfo();
cPref.reqGlEsVersion = fi.reqGlEsVersion;
pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("feature-group")) {
FeatureGroupInfo group = new FeatureGroupInfo();
ArrayList<FeatureInfo> features = null;
final int innerDepth = parser.getDepth();
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}
final String innerTagName = parser.getName();
if (innerTagName.equals("uses-feature")) {
FeatureInfo featureInfo = parseUsesFeature(res, attrs);
// FeatureGroups are stricter and mandate that
// any <uses-feature> declared are mandatory.
featureInfo.flags |= FeatureInfo.FLAG_REQUIRED;
features = ArrayUtils.add(features, featureInfo);
} else {
Slog.w(TAG, "Unknown element under <feature-group>: " + innerTagName +
" at " + mArchiveSourcePath + " " +
parser.getPositionDescription());
}
XmlUtils.skipCurrentTag(parser);
}
if (features != null) {
group.features = new FeatureInfo[features.size()];
group.features = features.toArray(group.features);
}
pkg.featureGroups = ArrayUtils.add(pkg.featureGroups, group);
} else if (tagName.equals("uses-sdk")) {
if (SDK_VERSION > 0) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesSdk);
int minVers = 0;
String minCode = null;
int targetVers = 0;
String targetCode = null;
TypedValue val = sa.peekValue(
com.android.internal.R.styleable.AndroidManifestUsesSdk_minSdkVersion);
if (val != null) {
if (val.type == TypedValue.TYPE_STRING && val.string != null) {
targetCode = minCode = val.string.toString();
} else {
// If it's not a string, it's an integer.
targetVers = minVers = val.data;
}
}
val = sa.peekValue(
com.android.internal.R.styleable.AndroidManifestUsesSdk_targetSdkVersion);
if (val != null) {
if (val.type == TypedValue.TYPE_STRING && val.string != null) {
targetCode = minCode = val.string.toString();
} else {
// If it's not a string, it's an integer.
targetVers = val.data;
}
}
sa.recycle();
if (minCode != null) {
boolean allowedCodename = false;
for (String codename : SDK_CODENAMES) {
if (minCode.equals(codename)) {
allowedCodename = true;
break;
}
}
if (!allowedCodename) {
if (SDK_CODENAMES.length > 0) {
outError[0] = "Requires development platform " + minCode
+ " (current platform is any of "
+ Arrays.toString(SDK_CODENAMES) + ")";
} else {
outError[0] = "Requires development platform " + minCode
+ " but this is a release platform.";
}
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}
} else if (minVers > SDK_VERSION) {
outError[0] = "Requires newer sdk version #" + minVers
+ " (current version is #" + SDK_VERSION + ")";
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}
if (targetCode != null) {
boolean allowedCodename = false;
for (String codename : SDK_CODENAMES) {
if (targetCode.equals(codename)) {
allowedCodename = true;
break;
}
}
if (!allowedCodename) {
if (SDK_CODENAMES.length > 0) {
outError[0] = "Requires development platform " + targetCode
+ " (current platform is any of "
+ Arrays.toString(SDK_CODENAMES) + ")";
} else {
outError[0] = "Requires development platform " + targetCode
+ " but this is a release platform.";
}
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}
// If the code matches, it definitely targets this SDK.
pkg.applicationInfo.targetSdkVersion
= android.os.Build.VERSION_CODES.CUR_DEVELOPMENT;
} else {
pkg.applicationInfo.targetSdkVersion = targetVers;
}
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("supports-screens")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestSupportsScreens);
pkg.applicationInfo.requiresSmallestWidthDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_requiresSmallestWidthDp,
0);
pkg.applicationInfo.compatibleWidthLimitDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_compatibleWidthLimitDp,
0);
pkg.applicationInfo.largestWidthLimitDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_largestWidthLimitDp,
0);
// This is a trick to get a boolean and still able to detect
// if a value was actually set.
supportsSmallScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_smallScreens,
supportsSmallScreens);
supportsNormalScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_normalScreens,
supportsNormalScreens);
supportsLargeScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_largeScreens,
supportsLargeScreens);
supportsXLargeScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_xlargeScreens,
supportsXLargeScreens);
resizeable = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_resizeable,
resizeable);
anyDensity = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_anyDensity,
anyDensity);
sa.recycle();
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("protected-broadcast")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestProtectedBroadcast);
// Note: don't allow this value to be a reference to a resource
// that may change.
String name = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestProtectedBroadcast_name);
sa.recycle();
if (name != null && (flags&PARSE_IS_SYSTEM) != 0) {
if (pkg.protectedBroadcasts == null) {
pkg.protectedBroadcasts = new ArrayList<String>();
}
if (!pkg.protectedBroadcasts.contains(name)) {
pkg.protectedBroadcasts.add(name.intern());
}
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("instrumentation")) {
if (parseInstrumentation(pkg, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("original-package")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestOriginalPackage);
String orig =sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);
if (!pkg.packageName.equals(orig)) {
if (pkg.mOriginalPackages == null) {
pkg.mOriginalPackages = new ArrayList<String>();
pkg.mRealPackage = pkg.packageName;
}
pkg.mOriginalPackages.add(orig);
}
sa.recycle();
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("adopt-permissions")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestOriginalPackage);
String name = sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);
sa.recycle();
if (name != null) {
if (pkg.mAdoptPermissions == null) {
pkg.mAdoptPermissions = new ArrayList<String>();
}
pkg.mAdoptPermissions.add(name);
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("uses-gl-texture")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;
} else if (tagName.equals("compatible-screens")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;
} else if (tagName.equals("supports-input")) {
XmlUtils.skipCurrentTag(parser);
continue;
} else if (tagName.equals("eat-comment")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;
} else if (RIGID_PARSER) {
outError[0] = "Bad element under <manifest>: "
+ parser.getName();
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
} else {
Slog.w(TAG, "Unknown element under <manifest>: " + parser.getName()
+ " at " + mArchiveSourcePath + " "
+ parser.getPositionDescription());
XmlUtils.skipCurrentTag(parser);
continue;
}
}在这个parseBaseApk方法中有一个while循环，该循环主要就是用于解析AndroidManifest.xml文件中的节点信息。在开始解析application节点的时候，同时调用了parseBaseApplication方法，该方法解析了application节点下的activity，service，broadcast，contentprovier等组件的定义信息：
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("activity")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, false,
owner.baseHardwareAccelerated);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.activities.add(a);
} else if (tagName.equals("receiver")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, true, false);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.receivers.add(a);
} else if (tagName.equals("service")) {
Service s = parseService(owner, res, parser, attrs, flags, outError);
if (s == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.services.add(s);
} else if (tagName.equals("provider")) {
Provider p = parseProvider(owner, res, parser, attrs, flags, outError);
if (p == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.providers.add(p);
} else if (tagName.equals("activity-alias")) {
Activity a = parseActivityAlias(owner, res, parser, attrs, flags, outError);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.activities.add(a);
} else if (parser.getName().equals("meta-data")) {
// note: application meta-data is stored off to the side, so it can
// remain null in the primary copy (we like to avoid extra copies because
// it can be large)
if ((owner.mAppMetaData = parseMetaData(res, parser, attrs, owner.mAppMetaData,
outError)) == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
} else if (tagName.equals("library")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestLibrary);
// Note: don't allow this value to be a reference to a resource
// that may change.
String lname = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestLibrary_name);
sa.recycle();
if (lname != null) {
lname = lname.intern();
if (!ArrayUtils.contains(owner.libraryNames, lname)) {
owner.libraryNames = ArrayUtils.add(owner.libraryNames, lname);
}
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("uses-library")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesLibrary);
// Note: don't allow this value to be a reference to a resource
// that may change.
String lname = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestUsesLibrary_name);
boolean req = sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesLibrary_required,
true);
sa.recycle();
if (lname != null) {
lname = lname.intern();
if (req) {
owner.usesLibraries = ArrayUtils.add(owner.usesLibraries, lname);
} else {
owner.usesOptionalLibraries = ArrayUtils.add(
owner.usesOptionalLibraries, lname);
}
}
XmlUtils.skipCurrentTag(parser);
} else if (tagName.equals("uses-package")) {
// Dependencies for app installers; we don't currently try to
// enforce this.
XmlUtils.skipCurrentTag(parser);
} else {
if (!RIGID_PARSER) {
Slog.w(TAG, "Unknown element under <application>: " + tagName
+ " at " + mArchiveSourcePath + " "
+ parser.getPositionDescription());
XmlUtils.skipCurrentTag(parser);
continue;
} else {
outError[0] = "Bad element under <application>: " + tagName;
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
}
}这样，经过这里循环遍历，整个androidManifest的节点信息就被解析并保存在了Package对象中。可以看到我们平时在Manifest中定义的各种节点，其实都是在这里有所体现。当androidManifest.xml文件被解析完成之后会调用我们刚刚介绍的scanPackageLI的重载方法，将解析完成的Package对象信息保存的Setting对象中，这个对象用于保存app的安装信息，具体实现是在方法：
private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
long currentTime, UserHandle user) throws PackageManagerException当解析完成manifest文件之后会调用其重载方法：
// Note that we invoke the following method only if we are about to unpack an application
PackageParser.Package scannedPkg = scanPackageLI(pkg, parseFlags, scanFlags
| SCAN_UPDATE_SIGNATURE, currentTime, user);这样，解析的manifest文件信息就会被保存到Settings中，并持久化，然后执行安装apk的操作，我们可以看一下该重载方法的具体实现：
private PackageParser.Package scanPackageLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
boolean success = false;
try {
final PackageParser.Package res = scanPackageDirtyLI(pkg, parseFlags, scanFlags,
currentTime, user);
success = true;
return res;
} finally {
if (!success && (scanFlags & SCAN_DELETE_DATA_ON_FAILURES) != 0) {
removeDataDirsLI(pkg.volumeUuid, pkg.packageName);
}
}
}可以发现其内部调用了scanPackageDirtyLI方法，这个方法就是实际实现持久化manifest信息并安装APK操作的：
private PackageParser.Package scanPackageDirtyLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
...
// And now re-install the app.
ret = createDataDirsLI(pkg.volumeUuid, pkgName, pkg.applicationInfo.uid,
pkg.applicationInfo.seinfo);
...
}可以发现其内部调用了createDataDirLI，该方法主要实现安装apk的操作。
private int createDataDirsLI(String volumeUuid, String packageName, int uid, String seinfo) {
int[] users = sUserManager.getUserIds();
int res = mInstaller.install(volumeUuid, packageName, uid, uid, seinfo);
if (res < 0) {
return res;
}
for (int user : users) {
if (user != 0) {
res = mInstaller.createUserData(volumeUuid, packageName,
UserHandle.getUid(user, uid), user, seinfo);
if (res < 0) {
return res;
}
}
}
return res;
}查看该方法的实现：
public int install(String uuid, String name, int uid, int gid, String seinfo) {
StringBuilder builder = new StringBuilder("install");
builder.append(' ');
builder.append(escapeNull(uuid));
builder.append(' ');
builder.append(name);
builder.append(' ');
builder.append(uid);
builder.append(' ');
builder.append(gid);
builder.append(' ');
builder.append(seinfo != null ? seinfo : "!");
return mInstaller.execute(builder.toString());
}怎么样？很熟悉吧，这里的Installer其实调用的就是我们平时运行android项目很熟悉的install命令，原来android系统安装apk文件底层都是调用的adb命令。
总结：
android系统启动之后会解析固定目录下的apk文件，并执行解析，持久化apk信息，重新安装等操作；
解析Manifest流程：Zygote进程 –> SystemServer进程 –> PackgeManagerService服务 –> scanDirLI方法 –> scanPackageLI方法 –> PackageParser.parserPackage方法；
解析完成Manifest之后会将apk的Manifest信息保存在Settings对象中并持久化，然后执行重新安装的操作；