Android: getSharedPreferences for session

Okay, check 开发者_运维技巧this source code:

public void checkSession() {
    SharedPreferences session = getSharedPreferences(PREFS_NAME, 1); 
    String getSession = session.getString("SESSION", null);
    Toast.makeText(this, getSession, Toast.LENGTH_SHORT).show();
    if(getSession.length() > 30) {
        Intent menu = new Intent(this, menu.class);
        startActivity(menu);
        finish();
    } 
    else 
    {   
    }
}

The problem is that "first time users" get crush.

When I disable the function, run the app and login the code creates session. After that when I logout, and restart the app - there's no problem. Any ideas?

First time the app runs and you don't have a value stored in the SharedPreference "SESSION" you return null as your default value. The getSession().length will then result in a NullPointerException.

You should do like this instead:

String getSession = session.getString("SESSION", "");

If getSession is null, I think Toast.makeText will fall over.* You might want to change the default return to "" from null. getSession.length() won't work if getSession is null either.

*Apparently that isn't true -- see TofferJ's comment.