Detect First Run | 易学教程

问题

I am trying to detect if my app has been run before, by using this code:

(This is in my default Android activity)

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    if (savedInstanceState == null) {
        Log.w("activity", "first time");
        setContentView(R.layout.activity_clean_weather);
    } else {

        Log.w("activity", "second time");
        setContentView(R.layout.activity_clean_weather);
    }


 }

When I first run the app it says first time, when I run it a second time, first time, and a third, first time....

I am using an actual Android device and I am not using the run button each time. I run the app once with the Eclipse run button, then I close the app and press on its icon on my phone.

Is there something wrong with my code?

回答1:

savedInstanceState is more for switching between states, like pausing/resuming, that kind of thing. It must always be created by you, also.

What you want in this case is SharedPreferences.

Something like this:

public static final String PREFS_NAME = "MyPrefsFile"; // Name of prefs file; don't change this after it's saved something

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0); // Get preferences file (0 = no option flags set)
    boolean firstRun = settings.getBoolean("firstRun", true); // Is it first run? If not specified, use "true"

    if (firstRun) {
        Log.w("activity", "first time");
        setContentView(R.layout.activity_clean_weather);

        SharedPreferences.Editor editor = settings.edit(); // Open the editor for our settings
        editor.putBoolean("firstRun", false); // It is no longer the first run
        editor.commit(); // Save all changed settings
    } else {
        Log.w("activity", "second time");
        setContentView(R.layout.activity_clean_weather);
    }

}

I basically took this code directly from the documentation for Storage Options and applied it to your situation. It's a good concept to learn early.

回答2:

You may use a self-defined shared preference to archive your goal.

回答3:

The fact is that savedInstanceState holds persistent data across activities. As such if you restart the app, savedInstanceState will be null across runs. You should either use a Preference or some data base entry to keep track of your first run. I myself use a SharedPreference for this purpose.

回答4:

savedInstanceState will be null if the app is not already loaded in memory. If you want to detect whether the app has run for the very first time, you have to apply different technique, such as using sharedPrefs / DB to store a property for the first run.

i.e. Check sharedPrefs for property "firstRun"

if exists, then it is not a first run

else it is the first run

set the firstRun property to true

来源：https://stackoverflow.com/questions/12765700/detect-first-run

标签

java

android

oncreate