Why getExternalFilesDirs() doesn't work on some devices?

Question

My app runs on Android 5.0. I use method getExternalFilesDirs() to check if external SD card is available. If it returns more than 1 File, that means external SD card exists.

But on some devices (for example Elephone G2), method getExternalFilesDirs() returns only one directory of primary storage. I'm sure that device has external SD card (/storage/sdcard1/).

Can any one give me the answer?

Answer 1

For getExternalFilesDirs to return the path of the sdcard, the OEM must have set the SECONDARY_STORAGE environment variable in the device specific init.rc file as mentioned here: https://source.android.com/devices/storage/config-example.html

Look at the source of getExternalFilesDirs here: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/app/ContextImpl.java#1039

The value is obtained from Environment.buildExternalStorageAppFilesDirs. Look at that source here: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/os/Environment.java#206

The value is dependent on mExternalDirsForApp, which in turn is populated by reading the contents of SECONDARY_STORAGE variable: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/os/Environment.java#136

As you can see, if the SECONDARY_STORAGE variable is not set, the sdcard path will not be returned. You can cross-check this by going to adb shell and looking at the output of echo $SECONDARY_STORAGE