Develop Reference

how to save files on externalStorage

I've already figured out that on some devices the externalStorage may be set as the device Storage, like on my Samsung Galaxy 4 10.1 with 5.0.2. Android OS.
The Question now is how can I still say to save it on the SD-Card ?
For Example:
private File makeFolder(String folder) {
File dir = new File(Environment.getExternalStorageDirectory() + "/" + folder + "/");
if (!(dir.exists() && dir.isDirectory())) {
dir.mkdirs();
}
return dir;
}
On my older Devices (like my Sony Ericson Pro) this works just fine. So how to solve this?

You are into a slightly complicated area of Android programming :)
I can not give you complete answer here, but I can give some pointers:
On almost all devices I've seen, Environment.getExternalStorageDirectory() will give you the path to the root directory of an emulated SDCARD - which is not a physical SDCARD. Manufacturers are free to map the physical SDCARD to this path - but usually, they emulate an SDCARD using internal memory)
And prior to Kitkat, there are no API available to even to determine the presence of a physical SDCARD.
From Kitkat onwards, you can see if a physical SDCARD is present by checking the result of appContext.getExternalFilesDirs() which will give you your app's private data directory path on all available storage media.
If a physical SDCARD is present and mounted, appContext.getExternalFilesDirs() will give you two paths are result. Then the first one is for the emulated SDCARD. You may notice that this path will contain same subpath that returned by Environment.getExternalStorageDirectory().
The following example will make this clearer. I am assuming a Samsung S4 with a real SDCARD inserted and mounted in it
The first path returned will be:
/storage/emulated/0/Android/data/com.example.yourapp/files.
The second path is interesting - as this path is your app's accessible area on the the real physical SDCARD. This path will be of the form:
/storage/extSdCard/Android/data/com.example.yourapp/files
This is the only path that you have write access in Kitkat.
So, from Kitkat onwards, from the presence of these two paths, (and added checks for mounted SDCARD), you can easily find out whether your app is running on a phone with real SDCARD or not. You can even parse the second path to get the root directory of the real SDCARD (just remove /Android/... substring from this path)
And yes, now you know why you are so restricted with real SDCARDs in Kitkat. As said in italics above, you have write access to only that directory on a physical SDCARd in Kitkat.
Now comes Marshmallow and things changes again. In Marshmallow you have a storage framework, using which you can present the user with a permission dialog box and you can tell him to grant your app complete access to whatever device or directory therein. Please search for "Intent.ACTION_OPEN_DOCUMENT_TREE" for nice tutorials.
So, in short, as of now, there is no nice way in Android to deal with SDCARD which works uniformly in all versions. Before Kitkat, it is a grey area, In Kitkat, you are severely restricted, and in Lollipop, you are stuck with a system Activity with an absurd looking GUI for permission and not so easy to use framework.

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.

Android. No SD card available

My friend is testing my application which uses the SD card to store some settings. He has a Samsung Galaxy S2 but he just told me that he hasn't got an SD card in his device. It seems that the device created a folder in the phone's memory which simulates the existence of an SD card and that is where all app files that used the Sdcard are stored.
Is this a feature available for all Android devices? Should I consider the fact that there is no SD card on a device or should I not bother? Not sure if I should check for SD card availability in my app or not.
P.S. I've just noticed that the same goes for the emulator if I don't specify memory for the SD card.

You definitely should check for sdcard availability. On some devices it might work (as you said), but on some not, and you could get a FileNotFoundException.
So it's worth checking.

String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.toString().equals(
state.toString())) {
//////then do your work here////////
}
another solution: https://stackoverflow.com/a/7429264/6451573

Android. Not enough room on sdcard

I don't have an Android device to test this (yeah, i know. Android developer without an Android device) but i was wondering if in case there is either NO sdcard in the device, or the sdcard is full, when i need to store some data during the execution of my app, will it return an IOException? Or will it just store it automatically in the phone's memory? OR what happens in this situation, and what are the best steps to pursue?

you could check if the sd card is mounted or not
Is there a way to tell if the sdcard is mounted vs not installed at all?
EDIT:
you can check the availaible space in your phone (sdcard/internal)
How to Check available space on android device ? on SD card?
you might find this useful too.. An IOException IS thrown if you exceed the storage limit.
IOException is thrown when SDCard is full

You can setup the emulator so it uses a SD card and then fill it up with for example "dd". This should give you an environment you can use to test your application in the case when there is no room left on your SD card.

write file to sd card and not usb storage

I am developing an application that needs to write files to the SD card. I am using GetExternalStoragePublicDirectory() to determine the directory to write to.
I have two phones I am developing with. On a Google Nexus S, running Android 4.0.4 (Ice cream sandwich) it is returning a directory on the SD card. However, on a Samsung Exhibit 2 running Android 2.3.5, it is writing directly to the USB storage on the phone.
Is there a way to force the SD card?
edit:
I found that getExternalStoragePublicDirectory(), and getExternalStorageDirectory() are always returning "/mnt/sdcard/". This is not actually the mount location for the sd card. On the Samsung Exhibit 2, this is the USB storage location. The card mount location is "/mnt/sdcard/external_sd". Is there a way to return this actual sd location?
I see that the camera and other apps have found a way to do it. The camera app has a "storage" setting with options "phone" and "memory card". If "memory card" is specified, images are actually stored on the sd card.

Is there a way to return this actual sd location?
No, sorry, not in the current Android SDK.
I see that the camera and other apps have found a way to do it.
Mostly, they will either be ones written by the device manufacturer, or are reading information via MediaStore, which should index both sources.

If you want to write to SD card only use
File mySdCardPath = Environment.getExternalStorageDirectory();
File dir = new File (mySdCardPath.getAbsolutePath() + "/yourDirectoryName");