I've been developing an app on nougat that creates a directory in the external storage.
I used to do it like this:
final File dir = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Chords/Processed Audio");
dir.mkdirs();
This code does not seem to work on API 26 (Android Oreo). The directory is not created.
How can I achieve the same thing, preferably that works on all android version from API 21 to API 26?
I have no problems running your existing code on a Nexus 5X running Android 8.0. Using adb shell ls /storage/emulated/0, I see Chores/, and inside there I see Processed Audio/. This is for an app with WRITE_EXTERNAL_STORAGE permission, including runtime permissions.
That being said, ideally, do not use string concatenation to create File objects. Instead, use:
final File dir = new File(new File(Environment.getExternalStorageDirectory(), "Chords"), "Processed Audio");