CODEWITHSUNDEEP
androidandroid-intentandroid-activityandroid-lifecycle
Daniel
Daniel

Reputation: 502

Android - Keep previously added intent extra when going up to parent activity

Currently I am working with Android and I still have some troubles with understanding the Activity lifecycle.

Let me show you my problem with an example:

My App contains a Navigation Drawer which allows to use to switch between different Fragments. One Fragment (Fragment A) is a list with some items. Clicking one item opens activity B which can be described as a detail view of the item. B receives all necessary information by an Intent, the item model implements Parcelable and it is put as an Extra to the Intent. A button of Activity B opens the map view Activity C.

A -(Item)-> B -> C

Using the Up button in the action bar of C crashes the app when the B Activity onCreate method calls 

Item item = bundle.getParcelable("com.example.myapp.model.Item");

Of course, because the detail view B gets all necessary information which has to be displayed from A. How can I solve that problem? I want to be able to store the item somehow when calling C and going up to B again. (Using the back button on C works fine)

Upvotes: 18

Views: 4503

Answers (3)

beetstra
beetstra

Reputation: 7952

** Do not assume activity B still exists when you press up from B **

You mentioned the crash occurs because 'normally'

the detail view B gets all necessary information which has to be displayed from A.

So in this flow activity C will have to provide that information to B. You can do this using the getParentActivityIntent method. The base implementation of that method looks at the parentActivityName attribute in your manifest to create an intent. If you override it (in activity C) you can add the extras you need.

@Nullable
@Override
public Intent getParentActivityIntent() {
    Intent intent = super.getParentActivityIntent();
    if (intent != null)
        enhanceParentActivityIntent(intent);
    return intent;
}

private void enhanceParentActivityIntent(@NonNull Intent intent) {
    intent.putExtra("...", "...");
}

Upvotes: 0

x-code
x-code

Reputation: 3000

If you have implemented up navigation as described in Providing up navigation on the android developers site, you should be able to fix the error simply by changing the launch mode for activity B to "singleTop.". Set this in the application's manifest.xml file, as follows:

<activity ... launchMode="singleTop" ... />

What's happening now, presumably because B's launch mode is standard, is that up navigation is launching a new instance of activity B; it doesn't get the extras that were provided originally by A.

When the launch mode is "singleTop" according to the linked document,

If the parent activity has launch mode singleTop, or the up intent contains FLAG_ACTIVITY_CLEAR_TOP, the parent activity is brought to the top of the stack, and receives the intent through its onNewIntent() method.

In onNewIntent(), I believe (please check this), that you can just ignore the new intent, because you want to continue using the intent from activity A.

Upvotes: 26

baronS
baronS

Reputation: 1084

I would use an application class to store the global data like so: Using the Android Application class to persist data This serves as a singleton object which can be referred to by all activities

Upvotes: -1

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