does object die navigating between activities?

I have an application that nav开发者_Python百科igates to the same activity but each time the activity loads with different parameters. In my application it's a parsed data content retrieved from url. First thing I want to ask: When I push the backbutton of my device I get my earlier activity without being recreated. Is the objects in this activities alive and can I reference them?

Second question is if my first question doesn't make sense, what do you advice me to do?

If you look at the Activity life cycle, you'll notice that as long as your phone has enough memory, your first activity is kept in memory, and with it any member with the data it contains.

But if your phone needs to have some memory, it can kill any activity kept in background (any activity but the one being shown to the user), which means that you'll loose any data that was in your first activity.

To know which happened, keep in mind that the onResume() method will always be called when your activity is brought to foreground (either on creation, or when you navigate back to it), but onCreate() will be called only when your application is created from scratch (meaning you don't have any saved data).

You should use the bundle mechanism to save data when your activity is paused, and load it when you come back to it. Read the paragraph about Saving Activity state in Android doc to see how to use this.

You are not guaranteed that in memory data will be around once you leave an Activity. Read through this part of the dev guide thoroughly to understand the lifecycle of an Activity: http://developer.android.com/guide/topics/fundamentals/activities.html

If you need to persist information, you should override the onPause, onStop, and/or onDestroy methods of your Activity. You can then save your state using SharedPreferences, the SQLite database, or even a flat file.

In the manifest file add the following to the activity:

android:launchMode="singleTop"

In your example what is happening is when you navigate back to the activity using the back button you are bringing up the activity from the stack. When you navigate to the activity inside of the app what is happening is a NEW activity is being created, while the original is still on the stack. The singleTop launch mode will pop the activity out of the stack if it is there when you navigate to it in the app, and only create a new activity if it is not on the stack.

Without singleTop each time you launch the activity in the app it will create a new instance and you will find there are times you have to hit the back button on the same activity more than once due to multiple instances.