Mana recovery issue

Question

We're making a game in Android Studio and we got stuck. The resource (mana) used for specific spells should recover on time, e.g. 1 mana point per 5 minutes. We don't really get how to make it recover while the game is off. Is there a method to check current date/time and count the amount of mana replenished? Converting date and time to String and comparing it with the new date/time seems to be an "exciting" work to do, but we would bypass these mechanics if there is a way. Thank you in advance.

score 0 · Answer 1 · answered Aug 24 '15 at 08:35

No need to work with Date objects, the simple usage of System.currentTimeMillis() should work. Here's a basic outline:

long mLastManaRefreshTime = System.currentTimeMillis();

void refreshMana()
{
    long timeDelta = System.currentTimeMillis() - mLastManaRefreshTime;

    mLastManaRefreshTime = System.currentTimeMillis();

    float totalManaToRefresh = (float)AMOUNT_TO_REFRESH_IN_ONE_MINUTE * ((float)timeDelta / 60000f);

    mMana += totalManaToRefresh;

    if (mMana > MAX_MANA)
       mMana = MAX_MANA;
}

This method is of course just an outline. You will need to call this once every update cycle. It will calculate how much time passed since the last time refreshMana was called, and replenish the required amount.

If you need this to work while the game is off, you can save the mLastManaRefreshTime to a SharedPreferences object and reload it when the game loads up again.

score 0 · Accepted Answer · edited May 23 '17 at 12:00

The best way to do this in the background is to register a receiver in your manifest. This means the receiver will keep listening for broadcasts even if the app is off.

What you need is this particular action when registering your receiver Intent.ACTION_TIME_TICK

There is a more detailed answer about this matter here Time change listener

Another solution is to use the Calendar class in java. With it you can get the exact minutes passed from a point in the past to this moment. This way you don't have to worry about parsing dates and similar. I can't provide you specific examples because me myself have not used the Calendar class very much, but I'm sure you can find lots of stuff in the official documentation and on stackoverflow about it.

score 0 · Answer 3 · edited May 23 '17 at 12:16

With System.currentTimeMillis() you can a current time-stamp in milliseconds. You could save the latest time-stamp in your Preferences with every 5 min tick of the running game. For the other case, when your App comes back from a state where it does not do this (i.e. called the first time, woken up etc.). Something like this:

int manacycles = ((int) (((System.currentTimeMillis() - oldtimestamp) / 1000) / 60) ) % 5;

would give you the number of Mana points you would have to add.

Alternately you could do the same thing with the Calendar class.

Also keep in mind players could cheat this way by simply changing their time. If your game is online you could get the time from the internet, with something like this:

 try {
        TimeTCPClient client = new TimeTCPClient();
        try {
            // Set timeout of 60 seconds
            client.setDefaultTimeout(60000);
            // Connecting to time server
            // Other time servers can be found at : http://tf.nist.gov/tf-cgi/servers.cgi#
            // Make sure that your program NEVER queries a server more frequently than once every 4 seconds
            client.connect("nist.time.nosc.us");
            System.out.println(client.getDate());
        } finally {
            client.disconnect();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

Mana recovery issue

3 Answers3