Can't write file on SD-card

Question

I'm trying to write a photo on the SD card without success.

I've got the permissions to write in the removable storage and the sd card is mounted.

Also, I checked that the path to the SD card exists and I have obtained a positive result.

Where it fails is when I use the mkdir() function. It returns false and no file is created.

I have tested on both a Samsung A6(Marshmallow) and a Samsung Tab4(Lollipop)

This is the snippet of code I'm using to retrieve the path to the SD-card.
Because the standard procedure didn't work with Samsung devices, I'm using this snippet of code that I took from a stackoverflow answer

The path returned with this function from the Samsung A6 is /storage/6DD9-1D15.

public String[] getStorageDirectories() {
    String[] storageDirectories;
    String rawSecondaryStoragesStr = System.getenv("SECONDARY_STORAGE");

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
        List<String> results = new ArrayList<String>();
        File[] externalDirs = getApplicationContext().getExternalFilesDirs(null);
        for (File file : externalDirs) {
            String path = file.getPath().split("/Android")[0];
            if ((Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP && Environment.isExternalStorageRemovable(file))
                    || rawSecondaryStoragesStr != null && rawSecondaryStoragesStr.contains(path)) {
                results.add(path);
            }
        }
        storageDirectories = results.toArray(new String[0]);
    } else {
        final Set<String> rv = new HashSet<String>();

        if (!TextUtils.isEmpty(rawSecondaryStoragesStr)) {
            final String[] rawSecondaryStorages = rawSecondaryStoragesStr.split(File.pathSeparator);
            Collections.addAll(rv, rawSecondaryStorages);
        }
        storageDirectories = rv.toArray(new String[rv.size()]);
    }
    return storageDirectories;
}

This, instead, is the code I'm using to write a folder in the DCMI Directory under the SD-card(in which I will put the photos)

public void mkFolder(String folderPath) { // make a folder under Environment.DIRECTORY_DCIM

    File folder = new File(folderPath);

    try {
        // MKDIRS returns false
        if (folder.mkdirs()) {
            Log.d(TAG, "folder created:" + folder.toString());
        } else {
            Log.d(TAG, "create folder fails:" + folder.toString());
        }
    } catch (Exception ecp) {
        ecp.printStackTrace();
    }
}

Answer 1

On API Level 18 and below, your getStorageDirectories() will go through its else block. That block assumes:

• that the SECONDARY_STORAGE environment variable exists... which is not required
• that the SECONDARY_STORAGE contains a delimited list of directories... which is not required
• that the list of directories matches removable storage options... which is not required
• that you can work with those directories... which is not required

On API Level 19+, your getStorageDirectories() code will go through its if block. There, you start off fine, calling getExternalFilesDirs(). If that method returns 2+ items, the second and subsequent ones point to removable storage, and specifically point to places on removable storage where you can read and write. Then, your code assumes:

• that the directory has an /Android path segment... which is not required
• that the portion of the directory path preceding /Android represents a location in which you can create files and directories... which is never true

You do not have filesystem-level access to removable storage, except in the specific directories returned by methods like getExternalFilesDirs().

So, either:

• Stick to the specific locations returned by getExternalFilesDirs(), or

• Switch to using the Storage Access Framework, allowing the user to choose where to store content (which may or may not be removable storage)