我如何检查是否开始活动。 安卓

Question

I'm new to Android. My MainActivity is a Login activity. I want to check if a user is logged in, then starting the activity again should not show MainActivity, it should directly display the Dashboard Activity. I'm checking the login on the basis of value stored in the shared preferences.

sharedPreferences = this.getSharedPreferences("LoginDetail", Context.MODE_PRIVATE);
    String id = sharedPreferences.getString("userId","");
    if(!id.equalsIgnoreCase("") && id.length() > 5)
    {
        Intent i = new Intent(MainActivity.this, StudentSignin.class);
        startActivity(i);
        MainActivity.this.finish();
    }

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

I'm Trying to do something like that in onCreate Method. If user is not logged in he/she must login to continue; Thanks in advance.

Answer 1

Set a splash screen to your app, make it the launcher activity, and decide there which activity should be shown.

public class Splash extends AppCompatActivity{

    public void onCreate...{
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splash);
        sharedPreferences = this.getSharedPreferences("LoginDetail", Context.MODE_PRIVATE);
        String id = sharedPreferences.getString("userId","");
        if(userLogged(){
            //Go to dashboard
        }else{
            //Go to login screen
        }
    }



}

Answer 2

You can tell if a an Activity is started based on the life cycle state it currently is in, ie onCreate, onStart, onResume, onPause, onStop, onDestory. It seems you want some sort of flag to query that indicates if an activity is started, unfortunately android doesn't have that faculty. But even better are the life cycles that I mentioned above, with those, you can get a very accurate gauge of where the Activity is ie if it is being created, starting, resuming, pausing, stopping or being destroyed. This allows developers to developer very complex app, that don'y only rely on when the activity is started.

What I recommend you doing is writing a check logged in function and a login function that you should call inside of onStart(). This lifecycle function is always called when an Activity becomes visible. The benefit of doing this is, that you can always check if a user logged in state has changed in this activity. The onCreate function only gets called once during an Activity's lifecycle and that is when it is created/recreated. This would handle the use case where the user isn't logged in, and they temporarily exit the app (they don't close the activity, but just press the home button) and they resume, they are indefinitely stuck and unable to login until they restart the app (kill the activity and restart it) because the login logic is inside of onCreate and it won't get called again. But putting the logic inside of onStart, which will get executed whenever the activity becomes visible again, the bug will be solved.

Furthermore, you should combine this logic with @Jonathan Aste's answer.