ActionBar.setTitle(int) on a null object reference

Question

i am working of shared preferences using listview.. i found an article on internet and that suits my purpose exactly...but the problem.. i am getting.. an error..and app crashes without launching an activity...

MainActivity.java

   public class MainActivity extends AppCompatActivity {
public Toolbar toolbar;
    private Fragment contentFragment;
    ProductListFragment pdtListFragment;
    FavoriteListFragment  favListFragment;

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

        toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        /*
         * This is called when orientation is changed.
         */
        if (savedInstanceState != null) {
            if (savedInstanceState.containsKey("content")) {
                String content = savedInstanceState.getString("content");
                if (content.equals(FavoriteListFragment.ARG_ITEM_ID)) {
                    if (fragmentManager.findFragmentByTag(FavoriteListFragment.ARG_ITEM_ID) != null) {
                        setFragmentTitle(R.string.favorites);
                        contentFragment = fragmentManager
                                .findFragmentByTag(FavoriteListFragment.ARG_ITEM_ID);
                    }
                }
            }
            if (fragmentManager.findFragmentByTag(ProductListFragment.ARG_ITEM_ID) != null) {
                pdtListFragment = (ProductListFragment) fragmentManager
                        .findFragmentByTag(ProductListFragment.ARG_ITEM_ID);
                contentFragment = pdtListFragment;
            }
        } else {
            pdtListFragment = new ProductListFragment();
            setFragmentTitle(R.string.app_name);
            switchContent(pdtListFragment, ProductListFragment.ARG_ITEM_ID);
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if (contentFragment instanceof FavoriteListFragment) {
            outState.putString("content", FavoriteListFragment.ARG_ITEM_ID);
        } else {
            outState.putString("content", ProductListFragment.ARG_ITEM_ID);
        }
        super.onSaveInstanceState(outState);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_favorites:
                setFragmentTitle(R.string.favorites);
                favListFragment = new FavoriteListFragment();
                switchContent(favListFragment, FavoriteListFragment.ARG_ITEM_ID);

                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void switchContent(Fragment fragment, String tag) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        while (fragmentManager.popBackStackImmediate());

        if (fragment != null) {
            FragmentTransaction transaction = fragmentManager
                    .beginTransaction();
            transaction.replace(R.id.content_frame, fragment, tag);
            //Only FavoriteListFragment is added to the back stack.
            if (!(fragment instanceof ProductListFragment)) {
                transaction.addToBackStack(tag);
            }
            transaction.commit();
            contentFragment = fragment;
        }
    }

    protected void setFragmentTitle(int resourseId) {

       getSupportActionBar().setTitle("my title");
    }


    @Override
    public void onBackPressed() {
        FragmentManager fm = getSupportFragmentManager();
        if (fm.getBackStackEntryCount() > 0) {
            super.onBackPressed();
        } else if (contentFragment instanceof ProductListFragment
                || fm.getBackStackEntryCount() == 0) {
            finish();
        }
    }
}

how can i resolve this error and make the code to work properly..

here is the internet source for this example project http://androidopentutorials.com/android-how-to-store-list-of-values-in-sharedpreferences/

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"
    tools:context=".MainActivity" >
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary">

    </android.support.v7.widget.Toolbar>
    <FrameLayout
        android:layout_below="@+id/toolbar"
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.devmani.mandy.demofavapp">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity" >

            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

styles xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">

        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>


    </style>

</resources>

ProductListFragment java

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemLongClickListener;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.Toast;


public class ProductListFragment extends Fragment implements
        OnItemClickListener, OnItemLongClickListener {

    public static final String ARG_ITEM_ID = "product_list";

    Activity activity;
    ListView productListView;
    List<Product> products;
    ProductListAdapter productListAdapter;

    SharedPreference sharedPreference;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        activity = getActivity();
        sharedPreference = new SharedPreference();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_product_list, container,
                false);
        findViewsById(view);

        setProducts();

        productListAdapter = new ProductListAdapter(activity, products);
        productListView.setAdapter(productListAdapter);
        productListView.setOnItemClickListener(this);
        productListView.setOnItemLongClickListener(this);
        return view;
    }

    private void setProducts() {

        Product product1 = new Product(1, "Dell XPS", "Dell XPS Laptop", 60000);
        Product product2 = new Product(2, "HP Pavilion G6-2014TX",
                "HP Pavilion G6-2014TX Laptop", 50000);
        Product product3 = new Product(3, "ProBook HP 4540",
                "ProBook HP 4540 Laptop", 45000);
        Product product4 = new Product(4, "HP Envy 4-1025TX",
                "HP Envy 4-1025TX Laptop", 46000);
        Product product5 = new Product(5, "Dell Inspiron",
                "Dell Inspiron Laptop", 48000);
        Product product6 = new Product(6, "Dell Vostro", "Dell Vostro Laptop",
                50000);
        Product product7 = new Product(7, "IdeaPad Z Series",
                "Lenovo IdeaPad Z Series Laptop", 40000);
        Product product8 = new Product(8, "ThinkPad X Series",
                "Lenovo ThinkPad X Series Laptop", 38000);
        Product product9 = new Product(9, "VAIO S Series",
                "Sony VAIO S Series Laptop", 39000);
        Product product10 = new Product(10, "Series 5",
                "Samsung Series 5 Laptop", 50000);

        products = new ArrayList<Product>();
        products.add(product1);
        products.add(product2);
        products.add(product3);
        products.add(product4);
        products.add(product5);
        products.add(product6);
        products.add(product7);
        products.add(product8);
        products.add(product9);
        products.add(product10);
    }

    private void findViewsById(View view) {
        productListView = (ListView) view.findViewById(R.id.list_product);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {
        Product product = (Product) parent.getItemAtPosition(position);
        Toast.makeText(activity, product.toString(), Toast.LENGTH_LONG).show();
    }

    @Override
    public boolean onItemLongClick(AdapterView<?> arg0, View view,
                                   int position, long arg3) {
        ImageView button = (ImageView) view.findViewById(R.id.imgbtn_favorite);

        String tag = button.getTag().toString();
        if (tag.equalsIgnoreCase("grey")) {
            sharedPreference.addFavorite(activity, products.get(position));
            Toast.makeText(activity,
                    activity.getResources().getString(R.string.add_favr),
                    Toast.LENGTH_SHORT).show();

            button.setTag("red");
            button.setImageResource(R.drawable.heart_red);
        } else {
            sharedPreference.removeFavorite(activity, products.get(position));
            button.setTag("grey");
            button.setImageResource(R.drawable.heart_grey);
            Toast.makeText(activity,
                    activity.getResources().getString(R.string.remove_favr),
                    Toast.LENGTH_SHORT).show();
        }

        return true;
    }

    @Override
    public void onResume() { 
        getActivity().getSupportActionBar().setTitle(R.string.app_name); 
        super.onResume(); 
}
}

Answer 1

Solution:

Write this as Global Variable, before onCreate():

public Toolbar toolbar;

then, inside your onCreate()'s after setContentView(..):

toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

Then, Instead of this:

((Toolbar) findViewById(R.id.toolbar)).setTitle(resourseId);

Use this:

getSupportActionBar().setTitle("My title");

Also, remove this setTitle(resourceId)

---

Your setFragmentTitle(..) should look like this:

private void setFragmentTitle(int resourseId) {

    getSupportActionBar().setTitle(resourseId);

}

Finally, Apply your theme styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">

        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>


    </style>

</resources>

---

If you use this: ((Toolbar) findViewById(R.id.toolbar)).setTitle(resourseId); it means that you are setting a title to a new toolbar instance rather than using a supported Actionbar which you already set on above code.

Hope this helps.

Answer 2

If you want just to change title then do as Umang said, but if you like to set your own custom toolbar, then add this line in the manifest under that activity:

android:theme="@style/AppTheme.NoActionBar"

Hope it works for you.