An example of when to have multiple "activities" in an Android application

Question

I seem to be missing something obvious here, why would I want more than one activity per application in Android? Does somebody have some solid examples?

Answer 1

Suppose you are creating a game. You need to have at least two activities - a welcome screen, and the actual game screen. The third activity in this example might be a settings page of the game.

Another example.

Suppose you are developing an application and you need to pop up a dialog, i.e. asking user to set username and password (Standard login screen). You might choose to create and activity and apply a dialog theme to it.

Think about it as the form of desktop application. you don't put everything on one form do you? :)

Answer 2

Sorantis' answer is spot on. Here are other thoughts as well:

Most Web applications, even AJAX-y ones, don't try to have everything in one single page. Some do, and those tend to be the ones that are slow as molasses to load (Evernote, I'm looking at you), have code that looks like a heaping mound of spaghetti, etc. Android is no different.

Also, state management for a super-complex Activity will be nasty, causing you problems with screen rotations and supporting being kicked out of RAM because you screw up onSaveInstanceState(). Memory management in Android assumes lots of cheap activities, not fewer massive ones. Intelligently handling the BACK button requires gobs of your own logic. If you want multiple entry points (e.g., Launcher icon and a MIME type handler and something some other app can call with startActivityForResult() and a search results handler), doing that in one activity will be a nightmare. And so on.

Answer 3

One very basic thing that makes having multiple activities in your program desirable is the use of the back button. I have a form in app after the user clicks search he is presented with another activity showing the results of the search. If he wants to change the search parameters he just can press back and without me doing anything particular he gets back to the search form. Doing this with one activity would be a lot of work for you.

The next thing is the memory management. Android will trigger the garbage collection automaticaly after changing activities that means my whole search form leaves the memory and doesn't take any resources away from the user.