How to pass Arguments to Fragment from Activity

Question

I have an activity which instantiates and populates a Fragment through a adopter class. I want to pass values/objects to this Fragment adopter class so that i can dictate layout etc.

I have tried passing bundles using the setArgument method but my code bombs out and not sure why. As i understand, i can collect the bundle at the onCreate method in the adopter class. I see the arguments are set correctly immediately after the commented code but alas it crashes after that and i don't understand why. If i remove the bundle code it doesnt crash. :(

Below is my code, does anybody know where i should put the bundle code, commented out?

public class LoginScreen extends ActionBarActivity {
    private final String ARG_SELECTED_LAYOUT_ID = "selectedLayoutId";
private final int DEFAULT_LAYOUT = R.layout.layout_list;

private int mSelectedLayoutId;

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

    ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    actionBar.setDisplayShowTitleEnabled(false);
    actionBar.setDisplayShowHomeEnabled(false);

    mSelectedLayoutId = DEFAULT_LAYOUT;
    if (savedInstanceState != null) {
        mSelectedLayoutId = savedInstanceState.getInt(ARG_SELECTED_LAYOUT_ID);
    }

    addLayoutTab(
            actionBar, R.layout.layout_list, R.drawable.ic_list, "list");
    addLayoutTab(
            actionBar, R.layout.layout_grid, R.drawable.ic_grid, "grid");
    addLayoutTab(
            actionBar, R.layout.layout_staggered_grid, R.drawable.ic_staggered, "staggered");
    addLayoutTab(
            actionBar, R.layout.layout_spannable_grid, R.drawable.ic_spannable, "spannable");
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt(ARG_SELECTED_LAYOUT_ID, mSelectedLayoutId);
}

private void addLayoutTab(ActionBar actionBar, int layoutId, int iconId, String tag) {
    ActionBar.Tab tab = actionBar.newTab()
            .setText("")
            .setIcon(iconId)
            .setTabListener(new TabListener(layoutId, tag));
    actionBar.addTab(tab, layoutId == mSelectedLayoutId);
}

public class TabListener implements ActionBar.TabListener {
    private LayoutFragment mFragment;
    private final int mLayoutId;
    private final String mTag;


    public TabListener(int layoutId, String tag) {
        mLayoutId = layoutId;
        mTag = tag;
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
        mFragment = (LayoutFragment) getSupportFragmentManager().findFragmentByTag(mTag);



        if (mFragment == null) {
            mFragment = (LayoutFragment) LayoutFragment.newInstance(mLayoutId);
            ft.add(R.id.content, mFragment, mTag);

        } else {
            ft.attach(mFragment);
        }


        /*
            Bundle bundle = new Bundle();
            bundle.putInt("noTiles", 4);
            mFragment.setArguments(bundle);           
        */

        mSelectedLayoutId = mFragment.getLayoutId();
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            ft.detach(mFragment);
        }
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }
}

}

Logcat

03-03 11:56:53.675  32507-32507/weebuns.predictionking E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: weebuns.predictionking, PID: 32507
    java.lang.RuntimeException: Unable to start activity ComponentInfo{weebuns.predictionking/weebuns.predictionking.LoginScreen}: java.lang.NullPointerException: Attempt to invoke virtual method 'void weebuns.predictionking.LayoutFragment.setArguments(android.os.Bundle)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void weebuns.predictionking.LayoutFragment.setArguments(android.os.Bundle)' on a null object reference

Answer 1

To pass argument to your fragment, it's recommended to create a public static method to instanciate your fragment like :

public static MyFragment newInstance(String firstArg) {
        MyFragment f = new MyFragment ();
        Bundle args = new Bundle();
        args.putString("ARG1", firstArg);
        f.setArguments(args);
        return f;
    }

And then retrieve your args in onCreateView() method like :

String arg = getArguments().getString("ARG1");

Use the static method to instanciate a new fragment with your arguments in other fragment or activities like :

MyFragment f = MyFragment.newInstance(myArg);