Android FileProvider for ext sdcard

i added this root-path as suggested by @Gubatron in my XML and it works.

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <external-path name="external_files" path="."/>
    <root-path name="external_files" path="/storage/" />
</paths>

Let's take a look at FileProvider code:

    private static PathStrategy parsePathStrategy(Context context, String authority)
        ...
        int type;
        while ((type = in.next()) != END_DOCUMENT) {
            if (type == START_TAG) {
                final String tag = in.getName();
                final String name = in.getAttributeValue(null, ATTR_NAME);
                String path = in.getAttributeValue(null, ATTR_PATH);
                File target = null;
                if (TAG_ROOT_PATH.equals(tag)) {
                    target = buildPath(DEVICE_ROOT, path);
                } else if (TAG_FILES_PATH.equals(tag)) {
                    target = buildPath(context.getFilesDir(), path);
                } else if (TAG_CACHE_PATH.equals(tag)) {
                    target = buildPath(context.getCacheDir(), path);
                } else if (TAG_EXTERNAL.equals(tag)) {
                    target = buildPath(Environment.getExternalStorageDirectory(), path);
                }
                if (target != null) {
                    strat.addRoot(name, target);
                }
            }
        }
        return strat;
    }

FileProvider accepted absolute pathes to directory with help of tag root-path (DEVICE_ROOT constant). So just add absolute path to your files folder in secondary external disc like below:

<root-path path="/storage/extSdCard/Android/data/com.edufii/files/image/" name="image-ext2" />
<root-path path="/storage/extSdCard/Android/data/com.edufii/files/video/" name="video-ext2" />
<root-path path="/storage/extSdCard/Android/data/com.edufii/files/datafile/" name="datafile-ext2" />
<root-path path="/storage/extSdCard/Android/data/com.edufii/files/audio/" name="audio-ext2" />

Note official documentation doesn't say anything about <root-path>, so it may changed in a future.

starting from android 4.4, normal applications are not allowed to access secondary external storage devices, i.e. sd card, except in their package-specific directories, even if you have requested WRITE_EXTERNAL_STORAGE permission.

The WRITE_EXTERNAL_STORAGE permission must only grant write access to the primary external storage on a device. Apps must not be allowed to write to secondary external storage devices, except in their package-specific directories as allowed by synthesized permissions. Restricting writes in this way ensures the system can clean up files when applications are uninstalled.

https://source.android.com/devices/storage/