Develop Reference

Verifying that a File path is a SD card

I've been looking for a way to get the SD card directory for a majority of the day. I've recently found out that the function call getExternalStorageDirectory under some circumstances returns a path that is on-board memory. I am supporting API 19 and above.
The common answer stackOverflow gives to get the SD card path is
Environment.getExternalStorageDirectory().getAbsolutePath();
which is not working for my devices because the external storage returned is non-removable memory (Samsung Tab S2).
I've been able to use getExternalFilesDirs to return the list of directories, and in my testing it will return two directories, the on-board memory location for the application and the SD card that I've mounted. However the function call
isExternalStorageRemovable was not introduced until API 21. This was the clearest candidate that I could find that would have satisfied what I am trying to do, which is make sure that I am actually writing to the external SD Card.
1) Is there a way to verify if the directory returned by getExternalFilesDirs is removable or external in API 19?
2) Can it be assumed that if the only storage use cases are "Internal Memory" and "Internal Memory and SD Card" that the SD card location will always be returned second from getExternalFilesDirs as has happened in my brief testing?

I've recently found out that the function call getExternalStorageDirectory under some circumstances returns a path that is on-board memory
External storage is not removable storage. On the vast majority of Android devices, getExternalStorageDirectory() returns a location that is part of the on-board flash. That has been the case for ~7 years, since the introduction of Android 3.0.
Is there a way to verify if the directory returned by getExternalFilesDirs is removable or external in API 19?
If getExternalFilesDirs() returns 2+ items, the second and subsequent ones are on removable storage.
Can it be assumed that if the only storage use cases are "Internal Memory" and "Internal Memory and SD Card"
That is not a safe assumption.
that the SD card location will always be returned second from getExternalFilesDirs as has happened in my brief testing?
The first entry returned by getExternalFilesDirs() is the same as what is returned by getExternalFilesDir() (the older, singular form). While the vast majority of Android devices have fixed external storage, there may be some devices where external storage is actually removable. In this case, the Android SDK and framework still consider this to be external storage — after all, that is what the device manufacturer told the firmware to do. And, in this case, the location returned first from getExternalFilesDirs() would be physically removable, even if it is not what Android developers typically think of as removable storage. This is a fringe scenario; I cannot name any current device models that have external storage implemented on a removable card.
Also, bear in mind that not all removable storage is in the form of a card. USB OTG thumb drives are also removable storage, as are more traditional thumb drives for those devices that have a USB Type A port (e.g., Android TV, Samsung Galaxy S8 in a DeX dock).
which is make sure that I am actually writing to the external SD Card.
I strongly recommend that you stop thinking in terms of media. Use things like the Storage Access Framework (e.g., ACTION_OPEN_DOCUMENT, ACTION_CREATE_DOCUMENT) to allow the user to choose places to store content from all possibilities at their disposal: external storage, removable storage, Google drive, Windows file servers, etc.

do all android devices have non-removable external storage?

This link here describes about the non removable external storage.
does all the android devices have non removable external storage ?

No, this depends completely on the manufacturer. Devices like the Nexus S, Galaxy Nexus and Nexus 4 have non removable external storage, while some devices like the Optimus One have only removable external storage. Some devices may even have two external storages, one a partition on the on board memory chip and another as an SD Card.
EDIT
As CommonsWare pointed out in the comments, as far as the standard Android SDK is concerned, you only have one external storage on the device (which you can get via Environment.getExternalStorageDirectory()). As the documentation states, this will return the primary external storage in the event of the presence of more than one external storage:
In devices with multiple "external" storage directories (such as both
secure app storage and mountable shared storage), this directory
represents the "primary" external storage that the user will interact
with.

From that link
Because the external storage may be unavailable—such as when the user has mounted the storage to a PC or has removed the SD card that provides the external storage—you should always verify that the volume is available before accessing it.

Android External Storage among mobile brands

I am facing interesting problem. I have discovered, that Samsung in it's own Android phones has two implementations of storage.
1st: /sdcard - is internal memory and /sdcard/external_sd is actually inserted memory card
2nd: /storage/sdcard0 - is internal memory and /storage/ExtSdCard is actually inserted memory card.
My app needs data to be stored in sd card, so I am facing problem, how to determine, which folder might be sd card link or not. Do you know situation of any other Android maker (LG, HTC, Sony), how to cope with external SD cards and how they are visible in android system?

It is really so simple. When you consider your samsung mobiles it is the internal storage that acts as your sdcard.
if you are looking for to save a file in Sdcard, you have to stop hard coding the path like,
/mnt/sdcard.. and so.
instead use, Environment.getExternalStorageDirectory();
This will return the path to your sdcard straight away.
And from there, add Environment.getExternalStorageDirectory()+File.separator+"your directoryname";
And this works for all brands not unique to Samsung.

read/write some files from internal storage at runtime

I am developing a program that need read/write some files from sdcard or internal storage at runtime. When I mount the sdcard in my phone it run correctly but if i unmount sdcard my application raises some error.
What I have to do for phones that have not card slot like Htc one x or phones that have not any sdcard inserted? how i can write on those phones storage? I don't want write this file into /data/data/my.app.package folder. I want write somewhere that files can be read from another apps.
first I check storage status with this code and if sdcard be inserted and writable i have not any problem. but if sdcard does not exists i realy don't know what i have to do.
string _location;
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
_location=Environment.getExternalStorageDirectory()+"/myfolder/";
Toast.makeText(context, _location, 1000).show();
}
else
{
_location="/myfolder/"
Toast.makeText(context, Environment.getExternalStorageDirectory().toString(), 1000).show();
}
mysync mys=new mysync(); // Asynctasc that writes some file on _location path
mys.execute(_location);
i am so confused and undortunately i haven't any phone with big internal storage. please help me.

I am developing a program that need read/write some files from sdcard or internal storage at runtime.
Here, and in your question title, you say you want to write to internal storage. Later, you say that you do not want to write to internal storage.
Which is it?
What I have to do for phones that have not card slot like Htc one x or phones that have not any sdcard inserted?
External storage != "sdcard". External storage can be whatever the device manufacturer wants, so long as it meets the terms of the Compatibility Definition Document. Hence, external storage can be removable (e.g., SD card) or not (e.g.,. dedicated portion of on-board flash). And, on Android 3.0+, external storage is merely a special subdirectory on the same partition that contains internal storage.
You only care about whether external storage is presently available or not. It should be available pretty much all of the time on Android 3.0+ devices. It will be unavailable on Android 1.x and 2.x devices if the device is plugged into a host computer and the host computer has mounted the device's external storage (e.g., as a drive letter on Windows).
if sdcard does not exists i realy don't know what i have to do.
You ask the user to please unmount their device from their host computer. Or, you decide to write to internal storage in those cases.

Programmatically accessing internal storage (not SD card) on Verizon HTC Droid Incredible (Android)

I'm trying to find information on how to programmatically access the HTC Droid Incredible's supposed 8GB of Internal Storage Memory.
To determine the External Storage (SD Card) Location, I'm using the command:
android.os.Environment.getExternalStorageDirectory().
I've not been able to find any corollary for Internal phone Storage.
In examining HTC/Google Nexus One, Motorola Droid, and HTC Dream/G1 phones, there (as would be expected) does not appear to be any Mount Point for such Arbitrary Internal Storage.
On these phones the Internal Storage is divided amongst /data, /system, and /cache partitions.
The Incredible's Internal Storage is certainly not going to be located in /system. /cache is also unlikely given that it is globally non-readable/non-executable.
I'd read in reviews that the phone will still be limited to 512MB or so for apps, suggesting that it is not simply a subdirectory of /data.
I do not have access to a Droid Incredible unit myself, of course.

There is more information here: Droid Incredible storage mount points. It seems that Droid Incredible mounts its internal storage to /emmc, supposedly mounted r/w. It is not yet verified whether the WRITE_EXTERNAL_STORAGE permission is necessary in order to gain r/w access - I'm trying to get this information from Google Code
I will probably solve this by allowing the user two options to store the data:
SD-Card
Droid Incredible-only Internal storage
Edit: It seems that the WRITE_EXTERNAL_STORAGE permission is sufficient: according to droidForums both /sdcard and /emmc has the same GID of 1015.
Edit2: According to Google Group Thread the Incredible returns /sdcard as the result value of Environment.getExternalStorageDirectory(). Therefore, the user needs to decide whether he wants to use /sdcard or /emmc. The auto-detection of Incredible may be based on existence of the /emmc path.

As you're aware access to internal storage is usually limited to certain directories for each application by permissions. This is to stop one application reading data from another and from accessing system files without using the APIs. This makes sense since, for example, if you had an internet banking application you wouldn't want other apps to be able to access any of its cached data.
Each application gets to store data in a directory under /data/data. However, normally you don't specify the paths explicitly but used methods like Context.openFileOutput() which creates the file in the appropriate subdirectory of your application's directly.
I agree with you that it is unlikely that the majority of the 8GB of the Incredible's storage will be used for the /data partition.
So if they are going to have a separate partition to allow music and photos to be stored easily on the phone's internal storage then they will have to do it in a way that's compatible with existing applications. This means using Environment.getExternalStorageDirectory() but since the Incredible also supports SD cards then you're right in that it's not obvious how this might work.
There is a thread on the Android Developers Google Group discussing this exact question. Whilst there isn't an answer (at the time of writing) for how the Incredible works there's a post which says the Samsung Galaxy solves the same problem in this way:
The internal storage is mounted at /sdcard
If an SD card is also available this can be found at /sdcard/sd
This seems a sensible solution since it will be compatible with existing applications, including those which have mistakenly hard coded /sdcard instead of using Environment.getExternalStorageDirectory().
So my advice would be to use Environment.getExternalStorageDirectory() when you're looking for large areas for storage - either SD card or internal to the phone - and hope that each phone returns something sensible.

Just simply use this:
String primary_sd = System.getenv("EXTERNAL_STORAGE");
if(primary_sd != null)
Log.i("EXTERNAL_STORAGE", primary_sd);
String secondary_sd = System.getenv("SECONDARY_STORAGE");
if(secondary_sd != null)
Log.i("SECONDARY_STORAGE", secondary_sd)