App files stored android

Scoped Storage in Android 10 & Android 11

A secure and advanced app storage system for Android.

A controversial storage access change, slated for Android 10, becomes mandatory for Android 11. This blog talks about scoped storage, How we can access it and what does it mean for our app?

Before Android 10, storage was divided into private storage and shared storage. Private storage’s(android/data/

) access and contribution was limited to owner app alone. Apart from private storage, rest of the storage was called shared storage which is where all the media and non-media files were being stored. Any app with storage permission would be able to access this part of storage.

What was the problem with earlier storage ?

Limited access: Most of the apps do not need the access of whole storage since their use case are limited to certain types of files or files they own. One such use case can be a grocery app or an e-commerce app which needs storage access only to ask user to upload their profile picture.

Security: With storage access, an app can access a document as vulnerable as your bank statement or personal files. How would you like that?

Data organisation: Data/Files related to an app was scattered at multiple places in Shared Storage. If you have to uninstall the app and you want to clear all the corresponding data, that would not come easy.

This is how it is solved now

With Android 10, Google started to restructure the storage and change the way app accesses the storage so that all the mentioned problems can be eliminated. This storage division is called scoped storage.

Idea behind scoped storage was to divide whole storage into multiple blocks. An app would be provided access to the storage blocks which has relevant data for the app. In addition, system will bind storage to owner apps so that it becomes easier for the system to locate relevant files, corresponding to an app. This would also help to remove app specific data once app is uninstalled unless user does not want to.

This is how storage is divided now:

This storage remains same as before. Its app’s own private directory (/app/data/

) where app has unlimited access to read and write.

This is further divided into Media and Download collection. Media collection stores Image, Audio and Video files. Download collection would take care of non-media files.

What all permissions app need to access the files from scoped storage?

Earlier there was one permission to read all the files and another to write. Now with scoped storage, access is allotted based upon storage type and the ownership of the content.

1. App will have unlimited access to their internal and external storage for both read & write operation.

2. App will have unrestricted access to contribute files ( Media & Non-Media) as long as the file is stored in organised collection.

3. Media collection contributed by other apps can be accessed using ‘READ_STORAGE_PERMISSION’ permission. ‘WRITE_STORAGE_PERMISSION’ permission will be deprecated from next version and if used, will work same as ‘READ_STORAGE_PERMISSION’.

4. Non Media files contributed by other apps can be accessed using Storage access framework API. No explicit permission is needed. This does not mean that App can get access to all the directories ( Root, android/Data , Download directory etc.). Once user grants access to it, it will be complete access. (Read, Modify, Delete).

This is how we can access non-media Files. Here i am trying to access PDF file.

If App wants to select a custom folder, intent ACTION_OPEN_DOCUMENT can be replaced with ACTION_OPEN_DOCUMENT_TREE. ACTION_OPEN_DOCUMENT_TREE is introduced in android 11. This access will be valid till user reboots device. If app wants to persist the access, while accessing URI using content resolver , content resolver has to call takePersistableUriPermission method.

If App wants to create a file such as an email app saving attachment, intent can be replaced with ACTION_CREATE_DOCUMENT.

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Note: Media location is considered sensitive data now and would not be available unless app has ACCESS_MEDIA_LOCATION permission. It’s not a run time permission and has to be included in manifest. However it would be good idea to check this if app highly depends upon metadata or is an enterprise application where admin can remove the permission. If you want exact bytes of stored media, ‘MediaStore.setRequireOriginal(photoUri)’ has to be called.

So now apps can get access to specific block of memory. But what if I am a back up app which needs to access everything?

In Android 10, users tried to access the directories using storage access framework. Storage access framework was not intended for this purpose. Also, User complained about confusing UX. For such apps, a special permission is introduced in android 11. To ask the permission, Apps have to submit a declaration form to Google play. Once user grants the permission to have a broad access then user will get an unfiltered view of MediaStore that include non-media file. However, your app will not have access to external app directories.

Unfiltered view of Mediastore…What if my app uses custom file picker which displays exact data directories?

There is nothing you can do about it. You might want to use system picker from now on.

Alright so till this point we understand the reason behind scoped storage and the permission/methods to access it. Now let’s talk about scoped storage API changes over android 10 & 11.

Scoped storage was introduced in Android 10 but there were some controversial decision which enforced google to make API changes in Android 11.

1. In Android 10 and 11, Scoped storage is default behaviour. However app can request legacy external storage in Android 10 which is not the case in 11. Additionally In Android 10, Apps which wanted broader access, tried to use Storage access framework to select the directories which was not the intended purpose of storage framework. In Android 11, special access permission is introduced. Once Google play white list the app, special permission can be asked to the user.

2. In Android 10, UI for scoped storage permission looked same as earlier android version. So it would be hard for user to know if they are giving access to scoped storage or whole storage. With Android 11, permission UI will be updated so that user can clearly differentiate between different permissions he is providing.

3. In Android 11, Media store has been updated. User can do bulk delete/edit of media files which was not the case in Android 10. Additionally, Copying and Editing of files is possible in 11 but recommended only for one-off edits and small sized files since copying files will clutter user’s disk storage.

4. Android 10 has lack of support for native libraries and file path. This is use-case for apps written in c, c++. This support has been added in Android 11, in-fact this is the only use case where developer is expected to write new code. Under the hood file path api is a proxy to media storage api. so if possible, call media store api directly.

What does it mean for you?

if your app has files stored in Shared storage or outside app directory, you need to move them to app directory if you plan to target android 10 and above. Starting with Android 10 you will lose access to it.

Scoped storage is here to solve long time privacy issue. Although there were lots of controversial decisions and negative feedback in Android 10, It is here to stay. Starting September 2020, apps must target android 10 or later so unless you are an app which does not use storage, it’s recommended to start using scoped storage.

Lastly, thank you for reading the article! Any questions and suggestions are most welcome. See you soon.

Microsoft Mobile Engineering

#Mobile development articles and news brought to you by #MobileDevs working at @Microsoft

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How to Correctly Store App-Specific Files in Android

Christophe Versieux (Waza_be) posted a rant about android developers’ bad habit to store files directly on the root of the sd card. I completely agree with the post. It’s bad usage to create app-specific folders directly at the root. If you install a lot of apps, the sd card’s root gets cluttered fast.

One comment also mentioned that most tutorials do not cover the app-specific folders, so let me correct that with a short tutorial on how to do it correctly.

App-specific files vs. app-independent files

If you need to store files there are generally two usage types:

• App independent data
• App specific data

I will cover both types in more detail in the following sections. But in short I would characterize those types as follows: App-specific files are those that only are useful for as long as the app is installed (e.g. ebooks in a proprietary format). App-independent files on the other hand are those that the user cares about regardless of the specific app that created them (e.g. photos).

App-independent files

This type of data is stuff your user very likely cares about, even if your app is no longer installed on the device. Examples are photos shot, images processed or sketched, code-files edited, audio files bought and so on.

For most of these types, Android provides special directories. A full list of directories that Android provides out of the box can be seen in the documentation of the Environment class. Those fields all start with «DIRECTORY». E.g. DIRECTORY_MUSIC or DIRECTORY_PICTURES.

Those files always have to be stored on the sd card (or the equivalent partition for devices that have no sd card slot like the Google Nexus line). The reason is, that those files tend to be quite large, that they need to be world-readable and that they must not be stored in a directory that get’s cleaned up when your app gets uninstalled. I will cover external storage in more detail in the following sections.

You can get access to the root of the sd card by calling the getExternalStorageDirectory() method on the Environment class.

And you can use getExternalStoragePublicDirectory(String type) to directly get a File object for any of the supported types:

It’s the usual Java IO API from here on.

App-specific files

This type of files is for any kind of data that only this specific app can or should make use of. This could be proprietary files like ebooks, media files that should not be available through the normal media players (e.g. thumbnails for CD covers), downloaded magazines, database files, preferences and so on.

App-specific files can be stored internally or externally (on the sd card) and the Android API helps you to find the appropriate directories.

What’s nice for app-specific folders that follow a certain naming convention is Android’s cleanup mechanism. Android takes care to delete these folder when users uninstall your app. This way Android gets rid of unnecessary files and users do not have to clean up manually after any deinstallation.

Internal storage versus external storage

You should know that there are two app-specific folders for any app. The internal one which you can use for private files and the external one. External storage refers to the sd card of Android devices or the equivalent partition that devices with no sd card option offer (e.g. the Nexus line).

Internal storage space can be limited

Especially for larger files you should prefer the external storage option. You should do so because internal storage space can be very limited depending on the device of your user. A probably extreme example is my old LG Optimus One that has only about 300 MB of internal storage. But with a 16 GB sd card I have plenty of external storage. Even if this device is one of the worst examples regarding internal storage, there are plenty of devices out there that also come with little internal storage. Not everyone uses high-end phones.

Permissions for writing to external storage

Whenever you want to access files on the external storage you need permissions to do so. Add this permissions to your manifest file:

The need to declare this permissions is a slight drawback compared to internal storage. Some users may be wary — especially if this adds to an already long list of permissions. But if you explain this in your app description you should be fine.

Note: For reading files of the sd card no permissions were needed prior to Jelly Bean. So you can leave this one out if your build target is lower than API level 16.

External storage might be unavailable

The biggest problem with external storage is, that it might be unmounted when you need it. That’s obviously the case when the sd card is ejected but also when your device is mounted for file access to your computer. Because of this, you always have to check, if the external storage is currently available:

Sometimes the external storage might be mounted read-only. If you only need to read data the following check is better suited for you:

This works since the value of the final field Environment.MEDIA_MOUNTED_READ_ONLY is «mounted_ro» . I actually do not like code, that uses knowledge of final fields’ value. In my opinion it would have been better, had Google chosen to use an integer so that we could use final fields as bitmasks to test for the state.

Internal app-specific directories

Android creates a directory private to your app for you. Your shared preferences go in here, as well as your SQLite databases, native libraries or cached files.

All app-specific files are within a folder named

Within this folder some common sub-folders might exist — depending on what your app needs:

• databases — for SQLite databases
• shared_prefs — for your preferences
• cache — for cache files and data
• lib — for native libraries
• files — for files that do not fit into other categories

The Context class provides some methods you can use to create new directories, open InputStreams and so on. The following table lists these methods:

Methods to help you with internal storage

Method	When to use
deleteFile(String name)	Deletes the file with the given name
fileList()	Returns a list of files
getDir(String name, int mode)	Returns a file object to this directory. If the directory doesn’t exist yet, it gets created.
getFilesDir()	Returns a File object pointing to the files directory
openFileInput(String name)	Opens an InputStream object to the file with the given name
openFileOutput(String name, int mode)	Opens an OutputStream object to the file with the given name. The file gets created if it does not exists

Some methods use a mode parameter. This can be any of the following constants of the Context class:

• MODE_APPEND
• MODE_PRIVATE
• MODE_WORLD_READABLE
• MODE_WORLD_WRITEABLE

These are int values and you can use the or operator («|») to combine them — e.g. to append to a world readable file:

External app-specific directories

This is where Waza_be’s rant comes into play — because too many apps ignore the correct handling of app-specific directories on external storage.

All external app-specific files should be stored within a folder named

Note that I use a relative path. This path is relative to the root of the sdcard. The convention of where sdcards are mounted, changed between Android releases.

It’s always good practice to use API calls instead of hard-coded values, but the fact that the mount-point has changed in the past should make you even more cautious.

Now for external files there exists only one method you can use:

If you pass in a null value the File object will point to the files directory. If you add any of the directory constants of the Environment class, you will get a File object pointing to a sub-directory within your files directory. If the directory doesn’t exits yet, Android creates it for you. If the external media is not mounted, the method returns null.

Note: This method has only been introduced with API Level 8 (that is Froyo or Android 2.2). In the next section I briefly touch on the issues you face when dealing with older devices.

Older devices

There are still devices out there on older versions, which you might want to support. In this case using the naming convention shown above is still a good idea.

Alas, neither the method getExternalFilesDir(String type) exists, nor does Android clean up after an app uninstall. But using the same naming convention still avoids too many irritating folders on the root of your sd card.

Cache

Many times you need to cache data you downloaded from the net or created within your app. Android allows you to use internal as well as external storage space to use the cache. But using the external storage can be risky, since your cache might be unavailable when you need it.

The Context object has two methods to get a File object for either the internal or the external cache directory:

You have to take care of the cache size yourself. Android deletes all files in both directories on an uninstallation of your app, but otherwise it’s up to you to clean up any cache files no longer needed.

If Android is running low on internal storage it cleans up cache files first but the API states explicitly that you should not rely on Android to clean up for you!

With the external cache storage Android doesn’t care at all. Even if the external storage is full, no cache files will be deleted.

Naming of the folder

The official naming convention for the folder contains your package name. Christophe Versieux (Waza_be) himself mentioned that he used to use the app name instead, since users are more familiar with the package name of the app.

Even though familiarity is something to consider, I do not agree with this statement. First of all the API call uses the package name, so why not use it. Only with this method you can rely to be on the safe side. Secondly Android only cleans up a folder using the package name. And finally you could get screwed since app names do not have to be unique. In this case you might end up doing stuff in your folder that clashes with the intentions of the other app.

Be aware of the «.nomedia»-switch

Android’s MediaScanner regularly scans the sd card for any media files and adds these to the public list of media files. Thus images will show up in the Gallery app or music files in audio players.

But that’s not always what you want. Sometimes those files really should be presented by your app only. That’s where «.nomedia» comes into play. If a folder contains a file named «.nomedia» it will be skipped by the MediaScanner and any media files will thus not show up in the public media list.

That’s another reason to use the standard app-specific folder. It contains the file «.nomedia» within the data directory so that any media files you add to your app-specific directory will not show up.

Lessons learned

In this tutorial you have heard about the difference between app-specific and app-independent files and how to apply this knowledge to Android.

Also you have seen how to use app-specific files on Android, and how to leverage the internal storage as well as the external storage.

In a follow up post I will cover how to add app-independent media files to the corresponding content providers, so that they show up immediately in the list of public media files. Stay tuned.

Edited:
Minor changes due to comments by +Alexandre Roman and +Cyril Mottier to my G+ announcement of this post.

Wolfram Rittmeyer lives in Germany and has been developing with Java for many years.

He has been interested in Android for quite a while and has been blogging about all kind of topics around Android.

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