Android write files to USB via OTG cable

Question

I\'ve been searching for many topics about android file writing, yet most of them wanted to write files to android internal storage. Others who wanted to write files on exte

Answer 1

From android 4.4, you can use Storage Access Framework to access to removable media (see https://commonsware.com/blog/2014/04/09/storage-situation-removable-storage.html). For example, I tried with success to copy a pdf file from local memory to removable memory connected by OTG adapter. The only limitation: the user has to choose a destination folder.

1) call Intent.ACTION_CREATE_DOCUMENT:

Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);
intent.setType("application/pdf");
intent.putExtra(Intent.EXTRA_TITLE, file.getName());
startActivityForResult(intent, REQUEST_CODE);

2) intercept the return intent

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data){
    if(requestCode == REQUEST_CODE) {
        if (resultCode != RESULT_OK) return;
        copyFile(fileToCopy, data.getData());
    }
}

3) use the ContentResolver to open the outputStream and use it to copy the file

private void copyFile(File src, Uri destUri) {
    BufferedInputStream bis = null;
    BufferedOutputStream bos = null;

    try {
        bis = new BufferedInputStream(new FileInputStream(src));
        bos = new BufferedOutputStream(getContentResolver().openOutputStream(destUri));
        byte[] buf = new byte[1024];
        bis.read(buf);
        do {
            bos.write(buf);
        } while(bis.read(buf) != -1);
    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (bis != null) bis.close();
            if (bos != null) bos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}