Question

Java Exception: http://hastebin.com/yiwecefifi.avrasm

I have an object, that I call Category, that my fragment (A CategoryFragment [extending ListFragment]) needs to have access to in order to fill the ListView with content.

Normally, this works fine. The app starts, the categories are created, and the lists show up (As I have several of these in a ViewPager).

However, after pressing Home and staying away for a bit, re-entering the app will cause a crash. Before I created a constructor with a parameter, it would give me a NullPointerException to the category. Since then, I decided to give it a constructor with the category object, and now it fails in this manner.

So then, my question is one of two things:

1. How do I force the instantiation of the fragment through my activity? or
2. How do I make Android keep my object? I assume it’ll need to be serializable, but how do I keep it available when the Fragment is created again?

The manifest data for this activity is below:

<activity
    android:launchMode="singleInstance"
    android:name=".NewsActivity"
    android:configChanges="orientation|keyboardHidden|screenSize|screenLayout|uiMode"
    android:label="@string/shortcut_name"
    android:theme="@style/Theme.BgsuNews" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

Answer 1

This link in the docs about saving activity state should be useful. Fragments also have the onSave/RestoreInstanceState() functions like activities. You would need to decide which class your Category object belongs to (the Activity or the Fragment), and save and restore your Category data via the Bundle passed to you in the onSave/RestoreInstanceState() functions of that class.

For another way to store work in progress there’s this approach, which may or may not be useful in your case. (It’s what I do wherever possible, and onSaveInstanceState() works well for everything else.)