How do you share variables with other activities easily?

Question

I am making a card game and I have an activity for discarding cards and an activity for showing the scores. The problem is I want to pass some objects (player and dealer hands) to the other activity so that I can set imageViews in the scores to the cards that are in the players hands. How can I do this? I don't care about security or anything I just want the easiest way.

Answer 1

Using bundles inside the intent isn't about security, it's because the Android guys made it that way plain and simple. In my opinion using bundles and intents to pass larger objects is not a good idea. it gets too complicated to implement, makes you get the object down to the primitives (when using parcelable) and also makes a copy on the other side in memory (you take one object, set everything inside the intent and then re-create it on the other side making a new copy out of it) which for objects that have a bigger memory footprint isn't good.

I would suggest:

1. either using a singleton store
2. Using the application class (which also acts like a singleton)

I am often using a singleton which has a hashMap inside where an integer key is generated by me (from atomic Integer) and an object placed inside the map. You just send the ID inside the intent as an extra and retrieve it on the other side by getting the key from the intent and accessing your singleton to retrieve and remove the object (from that map) and use it in your new activity/service.

Here is a sample of something like this:

(Note: this is a part from my lib for rest requests (https://github.com/darko1002001/android-rest-client) in case you want to see more details on how everything is implemented). in your case you will need to strip some of the code and replace it with your own, but the general idea is the same.

/**
 * @author Darko.Grozdanovski
 */
public class HttpRequestStore {

    public static final String TAG = HttpRequestStore.class.getSimpleName();

    public static final String KEY_ID = "id";
    public static final String IS_SUCCESSFUL = "isSuccessful";

    private static final HashMap<Integer, RequestWrapper> map = new HashMap<Integer, RequestWrapper>();

    private final AtomicInteger counter = new AtomicInteger();
    private static Class<?> executorServiceClass = HTTPRequestExecutorService.class;

    private final Context context;
    private static HttpRequestStore instance;

    private HttpRequestStore(final Context context) {
        this.context = context;
    }

    public static HttpRequestStore getInstance(final Context context) {
        if (instance == null) {
            instance = new HttpRequestStore(context.getApplicationContext());
        }
        return instance;
    }

    public static void init(final Class<?> executorServiceClass) {
        HttpRequestStore.executorServiceClass = executorServiceClass;
    }

    public Integer addRequest(final RequestWrapper block) {
        return addRequest(counter.incrementAndGet(), block);
    }

    public Integer addRequest(final Integer id, final RequestWrapper block) {
        map.put(id, block);
        return id;
    }

    public void removeBlock(final Integer id) {
        map.remove(id);
    }

    public RequestWrapper getRequest(final Integer id) {
        return map.remove(id);
    }

    public RequestWrapper getRequest(final Intent intent) {
        final Bundle extras = intent.getExtras();
        if (extras == null || extras.containsKey(KEY_ID) == false) {
            throw new RuntimeException("Intent Must be Filled with ID of the block");
        }
        final int id = extras.getInt(KEY_ID);
        return getRequest(id);
    }

    public Integer launchServiceIntent(final HttpRequest block) {
        return launchServiceIntent(block, null);
    }

    public Integer launchServiceIntent(final HttpRequest block, RequestOptions options) {
        if (executorServiceClass == null) {
            throw new RuntimeException("Initialize the Executor service class in a class extending application");
        }
        if (isServiceAvailable() == false) {
            throw new RuntimeException("Declare the " + executorServiceClass.getSimpleName() + " in your manifest");
        }
        final Intent service = new Intent(context, executorServiceClass);
        final RequestWrapper wrapper = new RequestWrapper(block, options);
        final Integer requestId = addRequest(wrapper);
        service.putExtra(KEY_ID, requestId);
        context.startService(service);
        return requestId;
    }

    public boolean isServiceAvailable() {
        final PackageManager packageManager = context.getPackageManager();
        final Intent intent = new Intent(context, executorServiceClass);
        final List<ResolveInfo> resolveInfo = packageManager.queryIntentServices(intent,
                PackageManager.MATCH_DEFAULT_ONLY);
        if (resolveInfo.size() > 0) {
            return true;
        }
        return false;
    }

}

Answer 2

You can use Bundle to share variables in other activities. If you want to pass your own class object in other activities use Parcelable to your class

Here's an example

public class Person implements Parcelable {
     private int age;
     private String name;    

     // Setters and Getters
     // ....


     public int describeContents() {
         return 0;
     }

     public void writeToParcel(Parcel out, int flags) {
         out.writeString(name);
         out.writeInt(age);
     }

     public static final Parcelable.Creator<Person> CREATOR
             = new Parcelable.Creator<Person>() {
         public Person createFromParcel(Parcel in) {
             return new Person(in);
         }

         public Person[] newArray(int size) {
             return new Person[size];
         }
     };

     private Person(Parcel in) {
         name = in.readString();
         age = in.readInt();
     }
 }

Insert your Person object in bundle

Intent i = new Intent();
Bundle b = new Bundle();
b.putParcelable("bob", new Person());

Getting Person object

Intent i = getIntent();
Bundle b = i.getExtras();

Person p = (Person) b.getParcelable("bob");

Answer 3

You can use either of Bundles or shared preferences for share variable or save variables for future use.

Example for shared preferences you can find here Example for bundles you can find here

Answer 4

Singleton will be the best approach

Answer 5

You can use intent extras,

Intent intent = new Intent(getBaseContext(), NewActivity.class);
intent.putExtra("DATA_KEY", data);
startActivity(intent)

The docs for Intents has more information (look at the section titled "Extras").