The terms "Internal Storage" and "External Storage" might be confusing at first, because Google's intentions are different from what we would expect & know from our day-to-day use of language: "External" doesn't necessarily mean the "SD Card". This guy made a great article about the terminology confusion
According to your intentions, you'd want to be working with the External Storage concept. The differences are well explained in the Documentation, but I'll shortly brief them to you here.
At the end I'll provide you an example, but first lets know the basics:
Internal Storage
- Files are accessible by only your app
- Files are removed when your app is uninstalled
- Files are always available (meaning they files will never be saved on a removable memory)
External Storage
- Files are fully readable by other apps (including any variant of File Manager app, in your case)
- Files aren't necessarily removed when your app is uninstalled - explained later
- Files availability isn't guaranteed (can be deleted by other apps / removable memory)
So now that we know you need External Storage, there are several things needed to be done before starting:
- Require Permissions (read/write) inside your
Manifest.xml file, depending on your needs:
<manifest ...>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
...
</manifest>
Each permission stands by its own, meaning you don't need to have both if, for example, you only wish to read files instead of writing them
- Verify that storage is available - this is done on runtime, and is well explained inside the documentation. We need to make sure the storage is mounted into the device / its state is not problematic somehow in a way that would cause a failure of read/write requests.
Example Time!
In the given method, we will save a text file inside the root directory.
Credits to this article
public void writeFileExternalStorage() {
//Text of the Document
String textToWrite = "bla bla bla";
//Checking the availability state of the External Storage.
String state = Environment.getExternalStorageState();
if (!Environment.MEDIA_MOUNTED.equals(state)) {
//If it isn't mounted - we can't write into it.
return;
}
//Create a new file that points to the root directory, with the given name:
File file = new File(getExternalFilesDir(null), filenameExternal);
//This point and below is responsible for the write operation
FileOutputStream outputStream = null;
try {
file.createNewFile();
//second argument of FileOutputStream constructor indicates whether
//to append or create new file if one exists
outputStream = new FileOutputStream(file, true);
outputStream.write(textToWrite.getBytes());
outputStream.flush();
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
I'd like to answer specifically to some of your questions:
do I need to create those folders in the android studio as adding folders? or do I need to create it from code?
Definitely not via the Android Studio. These are your projects folder, containing your code. The way to do it is mentioned above.
I couldn't find the folder with my app name and inside it my Databases and Images folders... What am I doing wrong?
Probably saved your files as Internal Storage ones / saved them as project folders as you mentioned earlier - and those wouldn't (and shouldn't) show up.
Useful things to know
There are 2 types of directories: public and private.
Private
- Not accessible by the Media Store
- Files are removed when app is uninstalled
- Retrieved by
getExternalFilesDir(...) method
Example: the WhatsApp directory (in my phone) is located right at the root level. Calling it would be: getExternalFilesDir("WhatsApp/...")
Public (Downloads/Movies/Images libraries)
- Files are scanned by the MediaStore
- Retrieved by
Environment.getExternalStoragePublicDirectory(...) method
Example: getting the Documents folder would look like: Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS)
