How to add collapsing toolbar with fragment in a single activity

Question

This is my MainActivity

public class ProjectDetailsActivity extends AppCompatActivity {

    private static final String TAG = ProjectDetailsActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_container);

        if (savedInstanceState == null) {
            addFragment(new ProjectDetailsFragment(), false);
        }

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar_detail);
        toolbar.setNavigationIcon(R.drawable.ic_action_back);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Button Clicked", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });



    }

    public void addFragment(Fragment f, boolean isAddToBack) {

        FragmentTransaction mFragmentTransaction = getSupportFragmentManager().beginTransaction();
        mFragmentTransaction.replace(R.id.fragment_container, f);
        if (isAddToBack) {
            mFragmentTransaction.addToBackStack(null);
        }
        mFragmentTransaction.commit();
    }

    @Override
    public void onBackPressed() {

        super.onBackPressed();
        overridePendingTransition(R.anim.abc_fade_in, R.anim.abc_fade_out);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(item.getItemId()==android.R.id.home){
            onBackPressed();
        }
        return super.onOptionsItemSelected(item);
    }

This my xml file

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.example.abcd.scrollappdemo.ScrollingActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/toolbar_scrollable_image_height"
        android:fitsSystemWindows="true"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/toolbar_layout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            >

            <ImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:src="@drawable/title_bg" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom|start"
                android:text="Garden Residency II"
                android:textColor="#ffffffff" />

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar_detail"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/AppTheme.PopupOverlay" />

        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>

    <include
        android:id="@+id/include_layout"
        layout="@layout/project_detail_content" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/fab_margin"
        app:layout_anchor="@id/app_bar"
        app:layout_anchorGravity="bottom|end" />

</android.support.design.widget.CoordinatorLayout>

This is my fragment class`

public class ProjectDetailsFragment extends BaseFragment implements View.OnClickListener {

    private static final String TAG = ProjectDetailsFragment.class.getSimpleName();

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View mView = inflater.inflate(R.layout.fragment_details, container, false);

        mappingWidgets(mView);

        return mView;
    }

    private void mappingWidgets(View v) {


    }

    @Override
    public void onClick(View v) {


    }

    }

Error Log :

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference
at com.abc.xyz.abcActivity.onCreate(ProjectDetailsActivity.java:32)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Activity theme in Mainfest is -

@style/Apptheme.Noactionbar

Answer 1

Just by putting these code in fragment I am able to access the actionbar from fragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View mView = inflater.inflate(R.layout.activity_detail, container, false);

    final Toolbar toolbar = (Toolbar) mView.findViewById(R.id.toolbar);


    AppCompatActivity activity = (AppCompatActivity) getActivity();
    activity.setSupportActionBar(toolbar);
    activity.setTitle("Project Details");
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    CollapsingToolbarLayout collapsingToolbar =
            (CollapsingToolbarLayout)mView.findViewById(R.id.collapsing_toolbar);