Android APK应用安装原理解析之AndroidManifest使用PackageParser.parserPackage原理分析

本文实例讲述了Android APK应用安装之AndroidManifest使用PackageParser.parserPackage原理。分享给大家供大家参考，具体如下：

Android 安装一个APK的时候首先会解析APK，这里要做很多事情，其中一个事情就是解析Manifest.xml文件，并将所有APK的Manifest封装到各种对象中并保存在内存当中

解析Manifest的类是非常重要的，该类就是frameworks\base\core\java\android\content\pm\PackageParser

PackageManagerService会调用PackageParser.parserPackage方法来解析APK清单，下面开始分析PackageParser的实现：

PackageParser是使用的XMLPullParser工具来对XML进行解析的，然后分别通过android.content.pm下各种xxxInfo类来进行封装：

public Package parsePackage(File sourceFile, String destCodePath,
  DisplayMetrics metrics, int flags) {
//最后要跑出的解析错误信息
mParseError = PackageManager.INSTALL_SUCCEEDED;
//获得要解析的文件的路径
mArchiveSourcePath = sourceFile.getPath();
//如果要解析的不是文件类型就跳过并且返回该方法
if (!sourceFile.isFile()) {
  Log.w(TAG, "Skipping dir: " + mArchiveSourcePath);
  //更新错误信息
  mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;
  return null;
}
//如果文件不是以.apk结尾并且flag没有确定一定是APK，那么也返回
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.
    Log.w(TAG, "Skipping non-package file: " + mArchiveSourcePath);
  }
  //更新错误信息
  mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;
  return null;
}
if ((flags&PARSE_CHATTY) != 0 && Config.LOGD) Log.d(
  TAG, "Scanning package: " + mArchiveSourcePath);
XmlResourceParser parser = null;
AssetManager assmgr = null;
boolean assetError = true;
try {
  assmgr = new AssetManager();
  //将一个文件添加到AssetManager中并返回一个唯一标识
  int cookie = assmgr.addAssetPath(mArchiveSourcePath);
  if(cookie != 0) {
    //通过标识去AssetManager中找到标识对应资源中的Manifest清单文件，并返回一个XML的解析器
    parser = assmgr.openXmlResourceParser(cookie, "AndroidManifest.xml");
    //走到这里证明一切顺利
    assetError = false;
  } else {
    Log.w(TAG, "Failed adding asset path:"+mArchiveSourcePath);
  }
} catch (Exception e) {
  Log.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.
  Resources res = new Resources(assmgr, metrics, null);
  //这个是真正在解析的package的方法，是private method
  pkg = parsePackage(res, parser, flags, errorText);
} catch (Exception e) {
  errorException = e;
  mParseError = PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;
}
if (pkg == null) {
  if (errorException != null) {
    Log.w(TAG, mArchiveSourcePath, errorException);
  } else {
    Log.w(TAG, mArchiveSourcePath + " (at "
        + parser.getPositionDescription()
        + "): " + errorText[0]);
  }
  parser.close();
  assmgr.close();
  if (mParseError == PackageManager.INSTALL_SUCCEEDED) {
    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
  }
  return null;
}

parserPackage调用了重载的另外一个parserPackage

private Package parsePackage(
    Resources res, XmlResourceParser parser, int flags, String[] outError)
    throws XmlPullParserException, IOException {
    AttributeSet attrs = parser;
    //每次调用这个方法时候清空这些变量
    mParseInstrumentationArgs = null;
    mParseActivityArgs = null;
    mParseServiceArgs = null;
    mParseProviderArgs = null;
    //这里调用这个方法获得包名
    String pkgName = parsePackageName(parser, attrs, flags, outError);
    if (pkgName == null) {
      mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_PACKAGE_NAME;
      return null;
    }
    int type;
    final Package pkg = new Package(pkgName);
    boolean foundApp = false;
    //从资源里获得AndroidManifest的数组
    TypedArray sa = res.obtainAttributes(attrs,
        com.android.internal.R.styleable.AndroidManifest);
    //继续挖掘出版本号
    pkg.mVersionCode = sa.getInteger(
        com.android.internal.R.styleable.AndroidManifest_versionCode, 0);
    //获取版本名
    pkg.mVersionName = sa.getNonConfigurationString(
        com.android.internal.R.styleable.AndroidManifest_versionName, 0);
    if (pkg.mVersionName != null) {
      pkg.mVersionName = pkg.mVersionName.intern();
    }
    //获得sharedUserId
    String str = sa.getNonConfigurationString(
        com.android.internal.R.styleable.AndroidManifest_sharedUserId, 0);
    if (str != null && str.length() > 0) {
      //验证包名是否符合规则
      String nameError = validateName(str, true);
      if (nameError != null && !"android".equals(pkgName)) {
        outError[0] = "<manifest> specifies bad sharedUserId name \""
          + str + "\": " + nameError;
        mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_SHARED_USER_ID;
        return null;
      }
      pkg.mSharedUserId = str.intern();
      pkg.mSharedUserLabel = sa.getResourceId(
          com.android.internal.R.styleable.AndroidManifest_sharedUserLabel, 0);
    }
    sa.recycle();
    //安装的位置
    pkg.installLocation = sa.getInteger(
        com.android.internal.R.styleable.AndroidManifest_installLocation,
        PARSE_DEFAULT_INSTALL_LOCATION);
    // Resource boolean are -1, so 1 means we don't know the value.
    int supportsSmallScreens = 1;
    int supportsNormalScreens = 1;
    int supportsLargeScreens = 1;
    int resizeable = 1;
    int anyDensity = 1;
    int outerDepth = parser.getDepth();
    //关键时刻到了，真正的开始解析了
    while ((type=parser.next()) != parser.END_DOCUMENT
        && (type != parser.END_TAG || parser.getDepth() > outerDepth)) {
      if (type == parser.END_TAG || type == parser.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 {
            Log.w(TAG, "<manifest> has more than one <application>");
            XmlUtils.skipCurrentTag(parser);
            continue;
          }
        }
        foundApp = true;
        if (!parseApplication(pkg, res, parser, attrs, flags, outError)) {
          return null;
        }
      } else if (tagName.equals("permission-group")) {
        if (parsePermissionGroup(pkg, 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")) {
        sa = res.obtainAttributes(attrs,
            com.android.internal.R.styleable.AndroidManifestUsesPermission);
        // 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.AndroidManifestUsesPermission_name);
        sa.recycle();
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这里分别把每种不同的element用不同的小方法去解析，他们的调用顺序是：

这些小方法里其实还是有很多小技巧的，有兴趣的话可以细细品位

更多关于Android相关内容感兴趣的读者可查看本站专题：《Android开发入门与进阶教程》、《Android调试技巧与常见问题解决方法汇总》、《Android基本组件用法总结》、《Android视图View技巧总结》、《Android布局layout技巧总结》及《Android控件用法总结》

希望本文所述对大家Android程序设计有所帮助。