public void onClick(@org.jetbrains.annotations.NotNull final View view) {
        if (view.getId() == R.id.btnLogon) {
            managerSecurityApi.login (etUsername.getText ().toString (), etPassword.getText ().toString (), new Callback<List<ObjectUser>> () {
                @Override
                public void onResponse (@NonNull Call<List<ObjectUser>> call, @NonNull Response<List<ObjectUser>> response) {
                    ObjectUser user = Gson.fromJson(response.body(), ObjectUser.class);

                        objectUser = new ObjectUser (
                            user.getId (),
                            user.getUsername (),
                            user.getGrade (),
                            user.getGradename(),
                            user.getDepartment (),
                            user.getDepartmentname()
                        );
                    getContentResolver ().delete (ProviderUser.CONTENT_URI, null, null);
                    etUsername.setText (R.string.blank);
                    etPassword.setText (R.string.blank);
                    ContentValues values = new ContentValues ();
                    values.put (ProviderUser.name, objectUser.getUsername ());
                    values.put (ProviderUser.grade, String.valueOf (objectUser.getGrade ()));
                    values.put (ProviderUser.gradename, objectUser.getGradename ());
                    values.put (ProviderUser.department, String.valueOf (objectUser.getDepartment ()));
                    values.put (ProviderUser.departmentname, objectUser.getDepartmentname());
                    getContentResolver ().insert (ProviderUser.CONTENT_URI, values);
                    showApps ();
                }
                @Override
                public void onFailure (@NonNull Call<List<ObjectUser>> call, @NonNull Throwable t) {
                    Toast.makeText (getApplicationContext (), t.getMessage (), Toast.LENGTH_SHORT).show ();
                }
            });
        } else {
            throw new IllegalStateException("Unexpected value: " + view.getId());
        }
    }