Put this in onCreate to get your facebook key

getFacebookKey

try {
            PackageInfo info = getPackageManager().getPackageInfo(
                    "YOUR.PACKAGE.NAME", //PUT YOUR PACKAGE NAME HERE (in lowercase)
                    PackageManager.GET_SIGNATURES);
            for (Signature signature : info.signatures) {
                MessageDigest md = MessageDigest.getInstance("SHA");
                md.update(signature.toByteArray());
                Log.e("KeyHash:", Base64.encodeToString(md.digest(), Base64.DEFAULT));
            }
        } catch (PackageManager.NameNotFoundException e) {
            Log.e("KeyHash:", e.getMessage());

        } catch (NoSuchAlgorithmException e) {
            Log.e("KeyHash:", e.getMessage());
        }