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it covers the basics of android as well as the advance topics in android application development
We are installing and uninstalling APK(s) every day, might be many time in a day, but have you try to get answer of following questions ?
1. What is Package Manager and Package Installer ?
PackageInstaller is the default application for Android to install interactively normal package. PackateInstaller provide user interface to manage applications/package. PackageInstaller calls InstallAppProgress activity to receives an instruction from the user. InstallAppProgress will ask Package Manager Service to install package via indalld. Source code is available at <Android Source>/packages/apps/PackageInstaller.
Package Manage is API which actually manage application install, uninstall, upgrade.When we install APK file, Package Manager parse the package(APK) file and display confirmation, When user press OK button, Package Manager call method named "installPackage" with these four parameters namely uri, installFlags, observer, installPackageName. Package Manager start one service named "package", now all fuzzy things happen in this service. you can check "PackageInstallerActivity.java" and "InstallAppProgress.java" in PackageInstaller source code. Package Manager Service running in system_service process and install daemon (installd) that runs as a native process both start at system boot time.
2. Where APK files stores in Android ?
1. Pre-Install (i.e. Camera, Calendar, Browser,etc.) APK stored in /system/app/
2. User Install (ApiDemo, Any.do, etc.) APK stored in /data/app/
3. Package Manager create data directory /data/data/<package name>/ to store database, shared preference, native library and cache data
You might see apk file and *.odex file for same APK, ODEX file is totally different discussion and purpose.
3. What is APK installation process in detail ?
Following process execute in Package Manager Service.
- Add a package to the queue for the installation process
- Determine the appropriate location of the package installation
- Determine installation Install / Update new
- A copy of the apk file to a given directory
- Determine the UID of the app
- Request to installd daemon process
- Create the application directory and set permissions
- Extraction of dex code to the cache directory
- To reflect and packages.list / system / data / packages.xml the latest status
- Broadcast to the system along with the name of the effect of the installation is complete package
Intent.ACTION_PACKAGE_ADDED: If the new ( Intent.ACTION_PACKAGE_REPLACED): the case of an update
4. How Package Manager store data ?
Package Manager store application information in three files, located in /data/system. Following sample is extracted from Android 4 ICS emulator image.
1. packages.xml :This file contain list of permissions and Packages/Applications.
This xml file stores two things 1. permissions 2. package (application), permission are store under <permissions> tag. Each Permission has three attributes namely name, package and protection. Name attribute has permission name which we are using in AndroidManifest.xml, package attribute indicate permission belong to package, In majority cases "android" is values because <permission> tag contain default permissions and protection indicate level of security.
package tag contain 10 attributes and few sub tags.
APK file installation location (/system/app/ or /data/app/)
native library (*.so file) default path is /data/data/<package name>/lib/
Store ApplicationInfo Flags [http://developer.android.com/reference/android/content/pm/ApplicationInfo.html]
timestamp in hex format
timestamp in hex format of first time installation
timestamp in hex format of last update
Version Code from AndroidManifest.xml file http://developer.android.com/guide/topics/manifest/manifest-element.html#vcode]
The name of Linux user ID that will be shared with other applications, It is same parameter which we define in AndroidManifest.xml [http://developer.android.com/guide/topics/manifest/manifest-element.html#uid]
The name of a Linux user ID
1. sigssignature information, count attribute represent number of cert tag.
2. cert contain certification key , index attribute represent global index of certificate, I observer that it increment when new certificate install with application.
3. perms contain permission which developer has set in AndroidManifest.xml
2. packages.list : It is simple text file contain package name, user id ,flag and data directory, I can't find any perfect description but I assume it that packages.list file may provide faster lookup of installed package because it file keep important information only.