How to pass an object from one activity to another on Android

Question

I am trying to work on sending an object of my customer class from one Activity and display it in another Activity.

The code for t

Answer 1

Android Activity objects can be destroyed and reconstituted. So, you will need to use another approach to look them - or any object they create!!! - up. That is, you could pass as static class reference but then the object handle (Java calls these "references", as does SmallTalk; but they are not references in the sense of C or assembly) will be possibly invalid later because a "feature" of Android OE is any Activity can be annihilated and reconstituted later.

The original question asked "How to pass object from one activity to another in Android" and nobody has answered that. For sure, you can serialized (Serializable, Parcelable, to/from JSON) and pass a copy of the object's data and a new object having the same data could be created; but it will NOT have the same references/handles. Also, many others mentioned you can store the reference in a static store. And that will work unless Android decides to onDestroy your Activity.

So, to really solve the original question you would need a static lookup plus each object will update its reference when/if it is recreated. E.g. each Android Activity would relist itself if its onCreate is called. You can also see how some people use the task list to search out an Activity by name. (system is temporarily destroying this instance of the activity to save space..getRunningTasks, the task list is effectively a specialized listing of the most recent object instance of each Activity).

For reference:

Stopped: "The activity is completely obscured by another activity (the activity is now in the "background"). A stopped activity is also still alive (the Activity object is retained in memory, it maintains all state and member information, but is not attached to the window manager). However, it is no longer visible to the user and it can be killed by the system when memory is needed elsewhere."

onDestroy "system is temporarily destroying this instance of the activity to save space."

So, the Message Bus is a workable solution. It basically "punts". Rather than try to have references to objects; then you re-architect your design to use MessagePassing instead of SequentialCode. Exponentially harder to debug; but it lets you ignore these sort of OperatingEnvironment understandings. Effectively, each object method access is inverted so the caller posts a Message and the object itself defines a handler for that message. Lots more code but can make it robust with the Android OE restrictions.

If all you want is the top Activity (typical thing in Android apps due to "Context" being needed everywhere), then you can just have each Activity lists itself as "top" in the static global space whenever its onResume is called. Then your AlertDialog or whatever which needs a context can just grab it from there. Also, its a bit yucky to use a global but can simplifying passing a Context up and down everywhere and, for sure, when you use a MessageBus then IT IS global anyways.