So I'm testing an app on a galaxy s3 on 4.1 and an older phone that runs 2.3. Neither phone has an sdcard in it but when I use Environment.getExternalStorageDirectory().getAbsolutePath() on my galaxy s3 it directs me to a folder called sdcard0 within a folder called storage. When I run it on the older phone it gives me the path mnt/sdcard/ and the sdcard folder is read only.
I am trying to create a folder in these directories. I can do it on my s3 but not on my older phone.
Is there something similar to the storage folder I'm missing on the older phone or can I write to the sdcard folder when there is no sd card present?
EDIT: I have the external write permissions in my manifest
On some phones, as the documentation suggests, the word external is not to be taken all too serious:
Note: don't be confused by the word "external" here. This
directory can better be thought as media/shared storage. It is a
filesystem that can hold a relatively large amount of data and that
is shared across all applications (does not enforce permissions).
Traditionally this is an SD card, but it may also be implemented as built-in storage in a device that is distinct from the protected
internal storage and can be mounted as a filesystem on a computer.
You can check if the storage is really external or not, using the Environment.isExternalStorageRemovable()-method. If it's not removable, you should always be able to write to it (given that you have the permissions declared).
If it is however removable, you'll need to check it's current state with Environment.getExternalStorageState(). Here's a quick example of how to use it:
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
// We can read and write!
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
// Mounted read only...
} else {
// Something is wrong...
}
So in these cases, you can write to the external storage.
Important: As the documentation specifies at multiple points, the above methods work for the primary external storage. Some devices (like the Motorola Xoom) have both an internal "external" storage, and an SD-Card.
There seems to be no "generalized" way to access the "secondary external storage" on such devices, although there is a standard now, introduced with Android 4.2
Devices may contain multiple instances of external storage, but
currently only the primary external storage is exposed to developers through API.
[...]
Starting in Android 4.2, devices can support multiple users, and
external storage must meet the following constraints:
[...]
Secondary external storage must not be writable by apps.
It seems to depend on the vendor which storage (internal or real external) is considered the primary one. Not much you can do here (without things getting messy...)
If there is no external storage present, you can use your applications Internal Storage, or the caching directory, depending on what kind of data you're storing.
Related
I have created one app which creates one file on external memory, but when I install it on different devices the files are created in internal sdcard in some device and not created in external(Physical) sd card.
My question is that. How do we decide between the internal or external sdcard.
Which has more preference to store file by default in android?
I use the
Environment.getExternalStorageDirectory()+ "PolicyTaskfile"+"/filename.txt";
It gives external or internal sdcard path depending on the device.
The short answer is that you do not get to pick. It's up to the OEM to decide whether external storage is truly SD card or just an internal storage device (for example: eMMC). With KitKat there is a notion of primary and secondary external storage, but no easy API to determine which you are using or which is really removable media.
I read alot about KITKAT and the prevention of writing to the secondary external sdcard.
It seems to be a new policy from google. I also read about storing the app's data under /externalsdcard/Android/data/.
Now my question, because I can't reproduce or test:
If the app is not allowed to write data directly under
< secundary external sdcard >, Will it then be possible to store the app's data under < secundary external sdcard >/Android/data/< app package name > ?
If possible. Could someone share a codesample ?
Never assume the removable secondary storage is larger than primar internal. On most modern devices internal storage can be up to 64 GB, but SD Card can be as small as 1 MB large (if user inserted small old card).
There is no way to distinguish which one is "external" using current APIs.
So the right way is using Context.getExternalFilesDirs() which returns all external storages to which you can store application-specific files without any permissions.
Use StatFs to find the largest storage available, and write data into it.
final File[] dirs = context.getExternalFilesDirs(null); //null means default type
//find a dir that has most of the space and save using StatFs
As the documentation says,
Returns absolute paths to application-specific directories on all external storage devices where the application can place persistent files it owns. These files are internal to the application, and not typically visible to the user as media.
This is like getFilesDir() in that these files will be deleted when the application is uninstalled, however there are some important differences:
External files are not always available: they will disappear if the user mounts the external storage on a computer or removes it.
There is no security enforced with these files.
External storage devices returned here are considered a permanent part of the device, including both emulated external storage and physical media slots, such as SD cards in a battery compartment. The returned paths do not include transient devices, such as USB flash drives.
An application may store data on any or all of the returned devices. For example, an app may choose to store large files on the device with the most available space, as measured by StatFs.
No permissions are required to read or write to the returned paths; they are always accessible to the calling app. Write access outside of these paths on secondary external storage devices is not available.
The first path returned is the same as getExternalFilesDir(String). Returned paths may be null if a storage device is unavailable.
My question is related to storing files on android devices. I want to store files created in an app to an SD, if it is mounted. The problem i am having is that the device I am using has a non-removable external storage unit. All attempts to find the SD card result in finding that external storage and the files being saved there. Is there a work around, or a way to get a list of the external storage's, or way to directly save to the SD card?
Android 4.4 offers getExternalFilesDirs() (note the plural name), which may be able to give you locations on removable media like an SD card, depending upon where it is located and how the manufacturer elected to interpret Google's rules.
Everything else on Android 4.4+, in terms of removable media, cannot be written to, except presumably via apps running with superuser privileges on rooted devices.
There is no support at all for anything beyond standard external storage on Android 4.3 and below. You will find various recipes online for trying to find other partitions that might represent removable media. These recipes are not supported, may not be reliable across all devices, and will not work on many Android 4.4+ devices.
Hence, I strongly encourage you to focus on standard external storage.
When using Eclipse file explorer to navigate my android directories, I saw mnt/sdcard and mnt/sdcard2, see below image:
When callingEnvironment.getExternalStorageDirectory() it returns mnt/sdcard, so I think the mnt/sdcad is the external storage , and mnt/sdcard2 is my actual SD card, is that true? And how can I use code to access files under mnt/sdcard2 ?
P.S.
It seems that I can access the external sd card directly:
File extStorageDir = Environment.getExternalStorageDirectory();
String parent = extStorageDir.getParent();
File extSdCardDir = new File(parent+"/sdcard2");
File file = new File(extSdCardDir, "DemoFile.jpg");
But I wonder the extra sd card will change name in other cases.
You are correct, getExternalStorage will return your built-in external storage. Unfortunately, as of Jelly Bean applications are no longer able to utilize the SD card if the device also has built-in storage as well as an SD card. You can try working around it through shell commands or hardcoding paths, but without root there is no reliable way to access it anymore.
This was just recently added the Android CTS, which all OEMs must comply with in order to use the Play store.
Compatibility Program Overview | Android Developers
Section 9.5 (pg. 34) of Android 4.3 Compatibility Definition
Device implementations that include multiple external storage paths
MUST NOT allow Android applications to write to the secondary external
storage.
Storage Options | Android Developers
It's possible that a device using a partition of the internal storage
for the external storage may also offer an SD card slot. In this case,
the SD card is not part of the external storage and your app cannot
access it (the extra storage is intended only for user-provided media
that the system scans).
Android 4.2 APIs | Android Developers
Saving data in a multi-user environment
Whenever your app saves user preferences, creates a database, or
writes a file to the user’s internal or external storage space, that
data is accessible only while running as that user.
To be certain that your app behaves properly in a multi-user
environment, do not refer to your internal app directory or external
storage location using hard-coded paths and instead always use the
appropriate APIs:
For access to internal storage, use getFilesDir(), getCacheDir(), or openFileOutput().
For access to external storage, use getExternalFilesDir() or getExternalStoragePublicDirectory().
No matter which of these APIs you use to save data for a given user,
the data will not be accessible while running as a different user.
From your app’s point of view, each user is running on a completely
separate device.
From the official documentation:
Using the External Storage
Every Android-compatible device supports a shared "external storage"
that you can use to save files. This can be a removable storage
media (such as an SD card) or an internal (non-removable)
storage ...
I'm really confused about this subject. From what I understand, using external storage doesn't necessarily mean to use a removable card, am I right? However, when talking about external storage, it's always referred as "sd card".
I'm developing an app that downloads .mp3 files from the internet. I want to save those files in the phone memory (don't want to use any removable device) but for what I have learned, those files have to be saved in external memory.However, I would like to offer the possibility of importing a file from a removable device. Where and how should I save those files?
Thanks
Difference between Internal Storage, External Storage (aka primary external storage) and Secondary External Storage?
Internal Storage: is storage that is not accessible by the user, except via installed apps (or by rooting their device). Example: data/data/app_packageName
External Storage has two types:
Primary External Storage: In built shared storage which is "accessible by the user by plugging in a USB cable and mounting it as a drive on a host computer". Example: When we say Nexus 5 32 GB.
Secondary External Storage: Removable storage. Example: SD Card.
When building an app that uses the internal storage, the Android OS creates a unique folder, which will only be accessible from the app, so no other app, or even the user, can see what's in the folder.
The external storage is more like a public storage, so for now, it's the sdcard, but could become any other type of storage (remote hard drive, or anything else).
The internal storage should only be used for application data, (preferences files and settings, sound or image media for the app to work).
If you intent to download many mp3s, i'd reccomend saving them to external storage, as the external storage is often bigger. Besides, storing data on the internal storage may prevent the user to install other applications.
The Internal and External Storage terminology according to Google/official Android docs is quite different from what we think.
According to official Android docs:-
Internal Storage: By default, files saved to the internal storage are private to your application and other applications cannot access them. When the user uninstalls your application, these files are removed/deleted. Your app user also can't access them using file manager; even after enabling "show hidden files" option in file manager. To access files in Internal Storage, you have to root your Android phone. So, this is NOT what we think as internal memory of the phone - Nexus 5's 32 GB internal memory.
External Storage:
This can be a removable storage media (such as an SD card) or an
internal (non-removable) storage
That means, both storage types like Nexus 6P's 64 GB internal memory and removable microSD card which we insert in phone's card slot are considered as External Storage.
Removable Storage means just microSD card storage, not the internal memory.
To store your app files in SD card, you may use File[] getExternalFilesDirs (String type) method in Context class. Generally, second returned path would be the storage path for microSD card (if any).
Note: I have edited - made my answer more useful after #Tunaki's comment.
From the Developer docs
All Android devices have two file storage areas: "internal" and "external" storage. These names come from the early days of Android, when most devices offered built-in non-volatile memory (internal storage), plus a removable storage medium such as a micro SD card (external storage). Some devices divide the permanent storage space into "internal" and "external" partitions, so even without a removable storage medium, there are always two storage spaces and the API behavior is the same whether the external storage is removable or not.
I think in the operating system, it defines external storage as anything not related to the actual OS filestructure. If you recall, when you write to 'internal storage', Android will make a folder privately for your application. So basically, if this is a hidden folder of some kind, it would mean that external storage could qualify as anything not being automatically hidden or managed directly by the OS. So this would mean that it would be up to the phone manufacturer about the definition of internal storage, as they could have 1 main piece of internal flash memory with two partitions on it. One partition meant to hold the os and the other meant to let you store everything on the phone.
Basically what I'm saying is: That's more a hardware related thing, and that the concept of 'external storage' could extend even to extra internal storage (flash memory) that the manufacturer added in. You could even consider storage options defined by the user as external storage as well.
Here's an updated answer for the latest Android (currently Android 13).
Internal storage used to mean the phone's internal memory and external storage used to mean, among other things, any inserted SD cards. Nowadays, this is not really the case because phones don't have SD cards any more. Phones without SD card slots still have "external storage" from the point of view of an app (eg Environment.getExternalStorageDirectory() still returns a valid location), but it's emulated - meaning it's actually a slice of internal storage.
This means one of the big differences between external and internal storage - which was that external was slower but bigger and internal fast and small - is no longer true.
Since Android 11, external storage has been scoped. This means apps get a folder of their own which is readable to them and unreadable to any other app (though see below). They can access this folder without permissions. Again, this brings external storage in line with internal. (Note scoped storage actually appeared in Android 10 but has only been enforced since Android 11).
But there are remaining differences between internal and external.
One big difference is that apps can still get a permission to read/write across all of external storage (MANAGE_EXTERNAL_STORAGE). This is hard to come by - users need to manually enable it by going into Settings, and apps which implement it are severely limited on the Play Store.
But it does mean that data written to external storage is less secure than that written to internal. Other apps may be able to eavesdrop on external.
The above is the TL;DR but there's a bit more to it. Here's a good article: https://medium.com/#tdcolvin/demystifying-internal-vs-external-storage-in-modern-android-c9c31cb8eeec