[android] How do I pass an object from one activity to another on Android?

I need to be able to use one object in multiple activities within my app, and it needs to be the same object. What is the best way to do this?

I have tried making the object "public static" so it can be accessed by other activities, but for some reason this just isn't cutting it. Is there another way of doing this?

This answer is specific to situations where the objects to be passed has nested class structure. With nested class structure, making it Parcelable or Serializeable is a bit tedious. And, the process of serialising an object is not efficient on Android. Consider the example below,

class Myclass    {
  int a;
  class SubClass    {
       int b;
  }
}

With Google's GSON library, you can directly parse an object into a JSON formatted String and convert it back to the object format after usage. For example,

MyClass src = new MyClass();
Gson gS = new Gson();
String target = gS.toJson(src); // Converts the object to a JSON String

Now you can pass this String across activities as a StringExtra with the activity intent.

Intent i = new Intent(FromActivity.this, ToActivity.class);
i.putExtra("MyObjectAsString", target);

Then in the receiving activity, create the original object from the string representation.

String target = getIntent().getStringExtra("MyObjectAsString");
MyClass src = gS.fromJson(target, MyClass.class); // Converts the JSON String to an Object

It keeps the original classes clean and reusable. Above of all, if these class objects are created from the web as JSON objects, then this solution is very efficient and time saving.

UPDATE

While the above explained method works for most situations, for obvious performance reasons, do not rely on Android's bundled-extra system to pass objects around. There are a number of solutions makes this process flexible and efficient, here are a few. Each has its own pros and cons.

1. Eventbus
2. Otto

Your object can also implement the Parcelable interface. Then you can use the Bundle.putParcelable() method and pass your object between activities within intent.

The Photostream application uses this approach and may be used as a reference.

It depends on the type of data you need access to. If you have some kind of data pool that needs to persist across Activitys then Erich's answer is the way to go. If you just need to pass a few objects from one activity to another then you can have them implement Serializable and pass them in the extras of the Intent to start the new Activity.

Maybe it's an unpopular answer, but in the past I've simply used a class that has a static reference to the object I want to persist through activities. So,

public class PersonHelper
{
    public static Person person;
}

I tried going down the Parcelable interface path, but ran into a number of issues with it and the overhead in your code was unappealing to me.

You can create a subclass of Application and store your shared object there. The Application object should exist for the lifetime of your app as long as there is some active component.

From your activities, you can access the application object via getApplication().