仅在首次运行时执行Android运行设置活动

Question

I am working on my first android app and i have a spinner on my main activity and when the user runs the app there after the landing screen or activity will be a different one based (not main). I am storing the selection from the spinner in a shared preferance and if this is set I would like to load a different activity on startup.

Code

private Spinner spinner;
private SharedPreferences favTeam;
//private SharedPreferences.Editor editor;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    /*
    if (favTeam.contains("team") && favTeam != null) {
        Intent intent = new Intent(this, MyTeamActivity.class);
        startActivity(intent);
    } else {
        System.out.println("-------- cant read from shared pref -----------");
    }

*/


    spinner = (Spinner) findViewById(R.id.selectTeam);
    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.teams_array, android.R.layout.simple_spinner_item);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(adapter);

}


public void submitMyTeam(View v){
    favTeam = this.getSharedPreferences("com.lonerganonline.league_of_ireland", Context.MODE_PRIVATE);
    //SharedPreferences favTeam = this.getSharedPreferences("com.lonerganonline.league_of_ireland", Context.MODE_PRIVATE);
    TextView txt = (TextView) findViewById(R.id.textView);
    String selectedTeam = spinner.getSelectedItem().toString();

    SharedPreferences.Editor editor = favTeam.edit();
    editor.putString("team", selectedTeam);
    editor.apply();
    Intent intent = new Intent(this, MyTeamActivity.class);

    txt.setText(favTeam.getString("team","Not Defined"));

    startActivity(intent);

}

i tried doing it by the commented out if statement in the code above but that led to fatal errors. any help would be greatly appreciated.

Answer 1

Because you are trying to read values from favTeam without initializing it. that why its not working and you are getting NullPointerException .

You have to initialize favteam ShardePreference before reading values from it,

using

favTeam = this.getSharedPreferences("com.lonerganonline.league_of_ireland", Context.MODE_PRIVATE);

in onCreate() So your code look like,

 favTeam = this.getSharedPreferences("com.lonerganonline.league_of_ireland", Context.MODE_PRIVATE);

   if (favTeam.contains("team") && favTeam != null) {
        Intent intent = new Intent(this, MyTeamActivity.class);
        startActivity(intent);
    } else {
        System.out.println("-------- cant read from shared pref -----------");
    }

If you still get errors then post error log.