应用重启后如何记分？

Question

I am making a two player game where I am able to have a rematch. I am also keeping track of the scores of each player. This is what my code for a rematch looks like:

public void rematch(View view) {
    Intent i = getBaseContext().getPackageManager()
            .getLaunchIntentForPackage( getBaseContext().getPackageName() );

    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    finish();
    startActivity(i);

}

The above code is called when the user clicks a rematch button. I basically just restart the application because it's easier than resetting all the variables I have. Anyways, to keep track of the scores, I am overriding the onStop() method like this:

@Override
protected  void onStop() {
    super.onStop();

    // We need an Editor object to make preference changes.
    // All objects are from android.context.Context
    SharedPreferences settings = getSharedPreferences(SCORES_NAME, 0);
    SharedPreferences.Editor editor = settings.edit();

    editor.putInt("scoreOne", p1Score);
    editor.putInt("scoreTwo", p2Score);

    editor.commit();
}

I am using shared preferences. Then, in my onCreate method, I get these shared preferences like this:

// Remember scores from previous games
    SharedPreferences settings = getSharedPreferences(SCORES_NAME, 0);
    p1Score = settings.getInt("scoreOne", 0);
    p2Score = settings.getInt("scoreTwo", 0);
    updateScores();

SCORES_NAME is public static final String SCORES_NAME = "MyScores";

This all isn't working. My scores after the game restarts are always back to 0. I was thinking of putting extras onto the intent in rematch() but I'm not sure how to access this intent in my onCreate() method. Any help is greatly appreciated!

Answer 1

You need to override onSaveInstanceState(Bundle savedInstanceState) and write the application state values you want to change to the Bundle parameter like this:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.
  savedInstanceState.putInt("scoreOne", p1Score);
  savedInstanceState.putInt("scoreTwo", p2Score);

  // etc.
}

The Bundle is essentially a way of storing a NVP ("Name-Value Pair") map, and it will get passed in to onCreate() and also onRestoreInstanceState() where you'd extract the values like this:

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  int p1Score = settings.getInt("scoreOne", 0);
    int p2Score = settings.getInt("scoreTwo", 0);
}

You would usually use this technique to store instance values for your application (selections, unsaved text, etc.).

Answer 2

Problem here is that you made the assumption that the new activity's onCreate() will be called after your first activity's onStop() has completed execution.

That's probably not an assumption you want to make, because they are two not completely related things.

Send the values you need to the newly created activity in the intent

public void rematch(View view) {
    Intent i = getBaseContext().getPackageManager()
            .getLaunchIntentForPackage( getBaseContext().getPackageName() );

    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    // Those next values will be there for sure in the new activity.
    i.putExtra("scoreOne", p1Score);
    i.putExtra("scoreTwo", p2Score);
    finish();
    startActivity(i);
}

And in the onCreate of your Activity can extract those values as follows

public void onCreate(Bundle savedInstance) {
    super.onCreate();
    ..

    int p1Score = getIntent().getIntExtra("scoreOne", 0);
    int p2Score = getIntent().getIntExtra("scoreTwo", 0);
}

Answer 3

You need to take the code from onStop and execute it before your call to finish() from the rematch method. Like this:

private void saveScores() {
    SharedPreferences settings = getSharedPreferences(SCORES_NAME, 0);
    SharedPreferences.Editor editor = settings.edit();

    editor.putInt("scoreOne", p1Score);
    editor.putInt("scoreTwo", p2Score);

    editor.commit();
}

And then call this function from rematch :

(...)
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

saveScores();

finish();
startActivity(i);

However, @elmorabea's solution is better is you are now only using SharedPreferences to pass values between activities.