getting a permission error even after permission read_contacts is declared

출처 : stackoverflow.com/questions/58712648/getting-a-permission-error-even-after-permission-read-contacts-is-declared

public class MainActivity extends AppCompatActivity {

    // Request code for READ_CONTACTS. It can be any number > 0.
    private static final int PERMISSIONS_REQUEST_READ_CONTACTS = 100;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Read and show the contacts
        showContacts();
    }

    /**
     * Show the contacts in the ListView.
     */
    private void showContacts() {
        // Check the SDK version and whether the permission is already granted or not.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && checkSelfPermission(Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{Manifest.permission.READ_CONTACTS}, PERMISSIONS_REQUEST_READ_CONTACTS);
            //After this point you wait for callback in onRequestPermissionsResult(int, String[], int[]) overriden method
        } else {
            // Android version is lesser than 6.0 or the permission is already granted.
            getContactNames();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions,
                                           int[] grantResults) {
        if (requestCode == PERMISSIONS_REQUEST_READ_CONTACTS) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // Permission is granted
                showContacts();
            } else {
                Toast.makeText(this, "Until you grant the permission, we canot display the names", Toast.LENGTH_SHORT).show();
            }
        }
    }

    /**
     * Read the name of all the contacts.
     *
     * @return a list of names.
     */
    private void getContactNames() {
        Uri uri = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;
        String[] projection    = new String[]          {ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME,
                ContactsContract.CommonDataKinds.Phone.NUMBER};

        Cursor people = getContentResolver().query(uri, projection, null,  null, null);

        int indexName = people.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME);
        int indexNumber = people.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);

        if(people.moveToFirst()) {
           do {
              String name   = people.getString(indexName);
              String number = people.getString(indexNumber);
              // add number to list
        // Do work...
           } while (people.moveToNext());
         }
         people.close();
    }
}