Add Nested Fragment after Parent Fragment view is already created

Question

I am trying to create a Fragment which has a public method for adding child Fragments to itself.

I've been reading through potentially similar questions but haven't found anything to help so far. I've reduced the problem down to a simple test app shown below.

Once fragA has been added to the main layout, I call the public method fragA.addFragB() to get it to add an instance of FragmentClassB to itself, but this causes the test app to crash, indicating "Activity has been destroyed" (see LogCat at the end of the post). Does this mean fragA has been destroyed so I can't add fragB to it, or does it mean fragB has been destroyed so I can't add it to fragA? Or does it mean something else entirely?

MainActivity.java

public class MainActivity extends FragmentActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        FragmentManager fragMan = getSupportFragmentManager();

        // add Fragment A to the main linear layout
        FragmentTransaction fragTrans = fragMan.beginTransaction();
        FragmentClassA fragA = new FragmentClassA();
        fragTrans.add(R.id.mainLinearLayout, fragA);
        fragTrans.addToBackStack("A");
        fragTrans.commit();

        // get Fragment A to add a Fragment B to itself
        fragA.addFragB();
    }

}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <LinearLayout
        android:id="@+id/mainLinearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:orientation="horizontal" >
    </LinearLayout>

</RelativeLayout>

FragmentClassA.java

public class FragmentClassA extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_a, container, false);
    }

    public void addFragB() {
        FragmentManager childFragMan = getChildFragmentManager();

        FragmentTransaction childFragTrans = childFragMan.beginTransaction();
        FragmentClassB fragB = new FragmentClassB();
        childFragTrans.add(R.id.fragA_LinearLayout, fragB);
        childFragTrans.addToBackStack("B");
        childFragTrans.commit();

    }
}

fragment_a.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragA_LinearLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >


</LinearLayout>

FragmentClassB.java

public class FragmentClassB extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_b, container, false);
    }

}

fragment_b.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

LogCat

11-18 16:17:05.627: E/AndroidRuntime(14351): FATAL EXCEPTION: main
11-18 16:17:05.627: E/AndroidRuntime(14351): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nestedfragmenttest/com.example.nestedfragmenttest.MainActivity}: java.lang.IllegalStateException: Activity has been destroyed
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.os.Looper.loop(Looper.java:137)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread.main(ActivityThread.java:5103)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at java.lang.reflect.Method.invokeNative(Native Method)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at java.lang.reflect.Method.invoke(Method.java:525)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at dalvik.system.NativeStart.main(Native Method)
11-18 16:17:05.627: E/AndroidRuntime(14351): Caused by: java.lang.IllegalStateException: Activity has been destroyed
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1365)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:595)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:574)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at com.example.nestedfragmenttest.FragmentClassA.addFragB(FragmentClassA.java:26)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at com.example.nestedfragmenttest.MainActivity.onCreate(MainActivity.java:25)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.Activity.performCreate(Activity.java:5133)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-18 16:17:05.627: E/AndroidRuntime(14351):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-18 16:17:05.627: E/AndroidRuntime(14351):    ... 11 more

EDIT:

ianhanniballake's answer and GrIsHu's later answer which expands on the same point have both been helpful in pointing out the root of the problem. However this raises a further issue.
The final intention is that FragmentClassA will be part of a library. It will be used in multiple situations and the number of FragmentClassB instances will vary, or there may even be none. Hence I need to be able to trigger the addition of the child fragments to any instance of FragmentClassA from the parent activity. I've just had a look at keeping fragA as a class level variable in MainActivity and then calling fragA.AddFragB() in the MainActivity's onActivityCreated() method, but it is not available to be overridden. Any thoughts?

GrIsHu · Accepted Answer · 2013-11-18 06:50:25Z

13

You can not directly load the fragment which you have declared in FragA. The FragmentA will be loaded first and then after you can load the FragmentB by calling the method addFragB() from your fragA's onCreateView() method.

Try out as below:

Remove the line fragA.addFragB(); from your MainActivity

public class MainActivity extends FragmentActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        FragmentManager fragMan = getSupportFragmentManager();

        // add Fragment A to the main linear layout
        FragmentTransaction fragTrans = fragMan.beginTransaction();
        FragmentClassA fragA = new FragmentClassA();
        fragTrans.add(R.id.mainLinearLayout, fragA);
        fragTrans.addToBackStack("A");
        fragTrans.commit();

    }

}

And try to load the FragmentB from FragmentA as below:

public class FragmentClassA extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        addFragB(); //Call and load fragment B here.
        return inflater.inflate(R.layout.fragment_a, container, false);
    }

    public void addFragB() {
        FragmentManager childFragMan = getChildFragmentManager();

        FragmentTransaction childFragTrans = childFragMan.beginTransaction();
        FragmentClassB fragB = new FragmentClassB();
        childFragTrans.add(R.id.fragA_LinearLayout, fragB);
        childFragTrans.addToBackStack("B");
        childFragTrans.commit();

    }
}

answered Nov 18, 2013 at 6:50

GrIsHu

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6 Comments

Sound Conception Over a year ago

This was helpful. Thanks. Please check my question Edit though.

GrIsHu Over a year ago

Well the thing which you want to implement is bit complicated and not valid way to implement. Can you tell me in which library your FragmentA class will reside ?

Sound Conception Over a year ago

To clarify, FragmentA will be part of an Android Library Project. It is to function along similar lines to a Tool Pallet such as you find in graphic editors, word processors etc. The contents of the Tool Pallets vary depending on what is logical for the file type opened in the app. I was thinking that moving to Nested Fragments might be quite convenient for re-arranging these Tool Pallets as needed. But from the sound of it, I should probably stick with my old method of building the Tool Pallets from Custom Compound Widgets rather than from Child Fragments. Is this what you're saying?

Sound Conception Over a year ago

Actually, now I think more about it, my test app doesn't properly reflect the real situation. The Tool Pallets (FragmentA) will be created but not populated when the app starts. They will not be populated until the user opens a file, so FragmentA will definitely already exist by then. Perhaps I can still use the Nested Fragment approach after all?

Johann Over a year ago

This solution assumes that FragmentB is a child of FragmentA. What if FragmentB was a sibling of FragmentA and you wanted to load FragmentB AFTER FragmentA has loaded? I doubt that you can use getChildFragmentManger for that.

|

ianhanniballake · Accepted Answer · 2013-11-18 06:35:03Z

4

FragmentTransaction.commit is not an immediate action as per the documentation therefore your fragA is not attached to an Activity (hence why it returns that the activity is destroyed) when you call fragA.addFragB().

You should instead call addFragB() in FragmentClassA.onCreate() to ensure fragA is attached to an activity and ready to initialize its own state.

answered Nov 18, 2013 at 6:35

ianhanniballake

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1 Comment

Sound Conception Over a year ago

This was helpful. Thanks. Please check my question Edit though.

MasterAM · Accepted Answer · 2014-03-08 19:25:14Z

Did you try adding this to child fragments:

@Override
    public void onDetach() {
        super.onDetach();

        try {
            Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
            childFragmentManager.setAccessible(true);
            childFragmentManager.set(this, null);

        } catch (NoSuchFieldException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

this will avoid runtime problems while switching between different fragments.

Let's say you have an activity with a Fragment, which will in turn have two child fragments: fragA and FragB.

You can implement child fragments something like this:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View root = inflater.inflate(R.layout.activity_mymessages, container, false);
    FragmentManager manager = getChildFragmentManager();
    FragmentTransaction ft = manager.beginTransaction();
    ft.replace(R.id.headlines, fragA);
    ft.replace(R.id.article, fragB);
    ft.commit();

    return root;
}

activity_mymessages.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal">
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="horizontal">
        <FrameLayout android:id="@+id/headlines"
            android:layout_height="match_parent"
            android:name="com.example.fragA"
            android:layout_width="103dp"
            android:layout_marginRight="10dp"/>
        <FrameLayout android:id="@+id/article"
            android:layout_height="fill_parent"
            android:name="com.example.fragB"
            android:layout_width="fill_parent" />
    </LinearLayout>

</FrameLayout>

Let me know if this works, if not I can provide working code from my GitHub.

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