抽象类扩展了Java和Android的多种类型的活动

Question

I am newbie in Java and Android programming. I just created simple app with login form and registration form. My login form and registration form works right now. I created abstract SignedActivity class which extends from Activity class. I want each activity which is available after login inherits from SignedActivity. If activity inherits from SignedActivity I can be sure that it is available only for signed users.

This is how SignedActivity looks:

public abstract class SignedActivity extends Activity {

public static String LOG_OUT_PATH = "/logOut.php";

private String sessionId;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    if (savedInstanceState != null) {
        String newSessionId = savedInstanceState.getString("sessionId");
        if (newSessionId instanceof String) {
            sessionId = newSessionId;
            return;
        }
    }
    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        String newSessionId = extras.getString("sessionId");
        if (newSessionId instanceof String) {
            sessionId = newSessionId;
            return;
        }
    }

    finish();
}

public void startSignedActivity(Intent intent) {
    intent.putExtra("sessionId", getSessionId());
    this.startActivity(intent);
}

protected String getSessionId() {
    return sessionId;
}

private void setSessionId(String newSessionId) {
    sessionId = newSessionId;
}

protected void logOut() {
    new RequestLogOutTask().execute(SignedActivity.LOG_OUT_PATH);
    setSessionId("");
    Intent intent = new Intent(this, SignInActivity.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK|Intent.FLAG_ACTIVITY_NEW_TASK);
    intent.putExtra("logOut", true);
    startActivity(intent);
}

public void onClickLogOut(View v) {
    logOut();
}

@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putString("sessionId", sessionId);
    super.onSaveInstanceState(savedInstanceState);
}

class RequestLogOutTask extends AsyncTask<String, Void, Void> {
    protected Void doInBackground(String... params) {
        (new RESTClient(Constants.REST_URL)).post(params[0], "");
        return null;
    }
}

}

My problem is that I sometimes need FragmentActivity instead of Activity after login. So I have to create SignedFragmentActivity which extends from FragmentActivity and it is basically the same as SignedActivity (only parent is different). So I have duplicate code - how to avoid it ?

Answer 1

You can move your SignedActivity code to ActivityHelper class:

class ActivityHelper {
    public static String initializeSessionId(Bundle savedInstanceState, Activity activity) {
        if (savedInstanceState != null) {
            String newSessionId = savedInstanceState.getString("sessionId");
            if (newSessionId instanceof String) {
                return newSessionId;
            }
        }
        Bundle extras = activity.getIntent().getExtras();
        if (extras != null) {
            String newSessionId = extras.getString("sessionId");
            if (newSessionId instanceof String) {
                return newSessionId;
            }
        }
        return null;
    }

    ...
}

Now you can use it in every Activity instance (ie FragmentActivity ):

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    sessionId = ActivityHelper.initializeSessionId(savedInstanceState, this);

    finish();
}
...