Android: How to put Class type in a Bundle?

Question

Is it possible to put a Class type in a Bundle ?

public static <T> Intent newInstance(Class<T> EventClass) {
    Bundle args = new Bundle();
    args.putXXXX(EventClass);
    Intent intent = new Intent(MyApplication.getInstance(), MyActivity.class);
    intent.putExtras(args);
    return intent;
}

Thanks guys !

Answer 1

You can simply use Class<T>.getCanonicalName() and then instantiate the class by that name when reading it from the Bundle.

The scenario makes sense if for example you want to communicate between Android components which singleton classes to use.

As an example you could have an action interface

public interface Action {
    void run(List<String> args, Context context);
}

that should perform specific tasks in a Fragment and you want to initialize Fragments with different sets of actions. Then your Fragment's instantiation methods can simply take Action classes as parameter:

public static void newInstance(String someParameter, Class<? extends Action>... actions) {
    Bundle arguments = new Bundle();
    String[] actionNames = new String[actions.length];
    for (int i = 0; i < actionNames.length; i++) {
        actionNames[i] = actions[i].getCanonicalName();
    }
    arguments.putStringArray(ARG_ACTIONS, actionNames);
}

Having defined some classes MyActionA implements Action and MyActionB implements Action you would create a Fragment with these actions in the following way:

Fragment myFragment = MyFragment.newInstance("some parameter", MyActionA.class, MyActionB.class)

The Fragment itself can use a list of actions (List<Action> action) as member variable which is initialized from the Bundle in onCreate():

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    for (String actionName : getArguments().getStringArray(ARG_ACTIONS)) {
        try {
            Class<? extends Action> actionClass = (Class<? extends Action>) Class.forName(actionName);
            Action action = actionClass.newInstance();
            actions.put(action.getName(), action);
        } catch (java.lang.InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
}

This by the way would fail with anonymous classes when trying to instantiate them as getCanonicalName() returns null for anonymous classes. So this method cannot be used to pass around anonymous classes, which I doubt to be possible at all.