handling configuration changes in fragments and activities

!!Configuration Changes.md

Configuration Changes

getting the cuttent configuration

in an activity:

Configuration config = ContextThemeWrapper.getResources().getConfiguration();

Saving UI state (simple)

1. override onSaveInstanceState(Bundle b)
2. override onRestoreInstanceState(Bundle b)

Note: bundle serilization is done on the main thread. Deserilise large items may block and risks an ANR

Hanling Configuration Change

Only do this if you must as there is lots of resource updating done by the framework for you.

1. override onConfigurationChanged(Configuration newConfig) and check device orientatino

Refrences

• https://github.com/codepath/android_guides/wiki/Handling-Configuration-Changes
• https://developer.android.com/guide/topics/resources/runtime-changes
• https://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html - a bit outdated.
• http://developer.android.com/guide/topics/resources/runtime-changes.html
• http://developer.android.com/training/basics/activity-lifecycle/recreating.html
• http://www.vogella.com/tutorials/AndroidLifeCycle/article.html#configurationchange
• http://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html
• http://www.intertech.com/Blog/saving-and-retrieving-android-instance-state-part-1/
• http://sunil-android.blogspot.com/2013/03/save-and-restore-instance-state.html
• https://medium.com/google-developers/activity-revival-and-the-case-of-the-rotating-device-167e34f9a30d#.nq3b23lxg

listview.java

// YourActivity.java
public final static String LIST_STATE_KEY = "recycler_list_state";
Parcelable listState;

protected void onSaveInstanceState(Bundle state) {
     super.onSaveInstanceState(state);
     // Save list state
     listState = mLayoutManager.onSaveInstanceState();
     state.putParcelable(LIST_STATE_KEY, listState);
}

protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);
    // Retrieve list state and list/item positions
    if(state != null)
        listState = state.getParcelable(LIST_STATE_KEY);
}

@Override
protected void onResume() {
    super.onResume();
    if (listState != null) {
        mLayoutManager.onRestoreInstanceState(listState);
    }
}

MainActivity.java

/** The standard mechanism for savig state.
*/

public class MainActivity extends Activity {
    static final String SOME_VALUE = "int_value";
    static final String SOME_OTHER_VALUE = "string_value";

/** handling config change */
@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);

    // Checks the orientation of the screen
    if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
        Toast.makeText(this, "landscape", Toast.LENGTH_SHORT).show();
    } else if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT){
        Toast.makeText(this, "portrait", Toast.LENGTH_SHORT).show();
    }
} 

/** alternatively if not handling config change - save state */
@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
        // Save custom values into the bundle
        savedInstanceState.putInt(SOME_VALUE, someIntValue);
        savedInstanceState.putString(SOME_OTHER_VALUE, someStringValue);
        // Always call the superclass so it can save the view hierarchy state
        super.onSaveInstanceState(savedInstanceState);
}

/** and restore it later */

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    // Always call the superclass so it can restore the view hierarchy
    super.onRestoreInstanceState(savedInstanceState);
    // Restore state members from saved instance
    someIntValue = savedInstanceState.getInt(SOME_VALUE);
    someStringValue = savedInstanceState.getString(SOME_OTHER_VALUE);
}
  
  
}

manifest.xml

<!-- skips restrart on  orientation|keyboardHidden configuration changes instead on-->
<activity android:name=".MyActivity"
          android:configChanges="orientation|keyboardHidden"
          android:label="@string/app_name">
</activity>

<!-- also one can suppress landscape layout conf change by lockinng screen orientation to portrait -->

<activity
    android:name="com.techblogon.screenorientationexample.MainActivity"
    android:screenOrientation="portrait"
    android:label="@string/app_name" >
</activity>

MySimpleFragment.java

/** We  can also saving and restoring Fragment State */

public class MySimpleFragment extends Fragment {
    private int someStateValue;
    private final String SOME_VALUE_KEY = "someValueToSave";
   
    // Fires when a configuration change occurs and fragment needs to save state
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt(SOME_VALUE_KEY, someStateValue);
        super.onSaveInstanceState(outState);
    }

   // Then we can pull data out of this saved state in onCreateView:

   // Inflate the view for the fragment based on layout XML
   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.my_simple_fragment, container, false);
        if (savedInstanceState != null) {
            someStateValue = savedInstanceState.getInt(SOME_VALUE_KEY);
            // Do something with value if needed
        }
        return view;
   }
}

RetainedFragment.java

/** alternatively we can store it in a fragment manager and use a tag to fetch it if it already exists */

public class RetainedFragment extends Fragment {
    // data object we want to retain
    private MyDataObject data;

    // this method is only called once for this fragment
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // retain this fragment when activity is re-initialized
        setRetainInstance(true);
    }

    public void setData(MyDataObject data) {
        this.data = data;
    }

    public MyDataObject getData() {
        return data;
    }
}