目錄

• System apps 與 normal app
• OBB File

System apps 與 normal app

The apps installed on your Android devices can be broadly categorized as system apps or user apps, based on their installation location.

normal app: /data partition
System apps: /system partition

    Some system apps are more system than others

    "signatureOrSystem" permissions are no longer available to all apps residing en the /system partition. Instead, there is a new /system/priv-app directory, and only apps whose APKs are in that directory are allowed to use signatureOrSystem permissions without sharing the platform cert. This will reduce the surface area for possible exploits of system- bundled applications to try to gain access to permission-guarded operations.

    The ApplicationInfo.FLAG_SYSTEM flag continues to mean what it is says in the documentation: it indicates that the application apk was bundled on the /system partition. A new hidden flag FLAG_PRIVILEGED has been introduced that reflects the actual right to access these permissions.
 

OBB File

OBB(Opaque Binary Blob) file is a file that developers create along with APK
The OBB files contain bundles of large assets(media and graphics)

Path
External SD Card > Android > OBB
External SD Card > Android > Data

settings > security > and make sure unknown sources is checked

* APK file be no more than 50MB

Google Play downloads the expansion file(s) at the same time it downloads the APK
("external" storage)

 - you have the option to add one or two expansion files to the APK
 - Each file can be up to 2GB

each expansion file plays a different role:

 - main expansion file
 - patch expansion file( intended for small updates to the main expansion )[patch carrier]
 

if your application update requires only a new patch expansion file,
you still must upload a new APK with an updated versionCode in the manifest.

When the user launches your application,
your app must check whether the expansion files are already saved on the device.

1. If yes, your app is ready to go.

2. If no, your app must download the expansion files over HTTP from Google Play.