void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Question

I have started to develop an application somehow i got an error in DetailActivity.java class and i couldn't identify please help me.Thanks in advance

public class PrayerDetailActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_prayer_detail);
    Toolbar toolbar = (Toolbar) findViewById(R.id.detail_toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own detail action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    // Show the Up button in the action bar.
    ActionBar actionBar = getSupportActionBar();
    if (actionBar != null) {
        actionBar.setDisplayHomeAsUpEnabled(true);
    }

    // savedInstanceState is non-null when there is fragment state
    // saved from previous configurations of this activity
    // (e.g. when rotating the screen from portrait to landscape).
    // In this case, the fragment will automatically be re-added
    // to its container so we don't need to manually add it.
    // For more information, see the Fragments API guide at:
    //
    // http://developer.android.com/guide/components/fragments.html
    //
    if (savedInstanceState == null) {
        // Create the detail fragment and add it to the activity
        // using a fragment transaction.
        Bundle arguments = new Bundle();
        arguments.putString(PrayerDetailFragment.ARG_ITEM_ID,
                getIntent().getStringExtra(PrayerDetailFragment.ARG_ITEM_ID));
        PrayerDetailFragment fragment = new PrayerDetailFragment();
        fragment.setArguments(arguments);
        getSupportFragmentManager().beginTransaction()
                .add(R.id.prayer_detail_container, fragment)
                .commit();
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == android.R.id.home) {
        // This ID represents the Home or Up button. In the case of this
        // activity, the Up button is shown. For
        // more details, see the Navigation pattern on Android Design:
        //
        // http://developer.android.com/design/patterns/navigation.html#up-vs-back
        //
        navigateUpTo(new Intent(this, PrayerListActivity.class));
        return true;
    }
    return super.onOptionsItemSelected(item);
}

} and my xml file is

<android.support.design.widget.AppBarLayout
    android:id="@+id/app_bar"
    android:layout_width="match_parent"
    android:layout_height="@dimen/app_bar_height"
    android:fitsSystemWindows="true"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

    <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"
        app:toolbarId="@+id/toolbar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/detail_toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_collapseMode="pin"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

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

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

<android.support.v4.widget.NestedScrollView
    android:id="@+id/prayer_detail_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior" />

The error displayed is

02-09 23:39:45.711 8201-8220/com.jen.jennings.catholicprayers E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab792700
02-09 23:39:54.364 8201-8220/com.jen.jennings.catholicprayers E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab792700
02-09 23:39:55.868 8201-8201/com.jen.jennings.catholicprayers E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: com.jen.jennings.catholicprayers, PID: 8201


                                              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jen.jennings.catholicprayers/com.jen.jennings.catholicprayers.PrayerDetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                            at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                            at android.app.ActivityThread$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$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                            at com.jen.jennings.catholicprayers.PrayerDetailActivity.onCreate(PrayerDetailActivity.java:29)
                                                                            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)

 

PLEASE HELP ME

Answer 1

In your xml there is no FloatingActionButton declared.

And you are trying to use it in onCreate().

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

Either remove it from onCreate() method of your activity or declare it in xml layout.

Answer 2

Main problem is your activity could not find the fab reference from the xml

If you really want FloatingActionButton then add bellow code at end of all view and before complete coordinator view.

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@android:drawable/ic_dialog_email" />

Else you can remove code and object of FloatingActionButton from your activity.

Answer 3

The problem is on those lines of code :

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        Snackbar.make(view, "Replace with your own detail action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show();
    }
});

Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Since in your xml doesn't appears any FloatingActionButton so if you put this in your onCreate everytime that your Acticity enters in onCreate() it will find this id R.id.fab and it's NULL because it doesn't exist.

Answer 4

Probably findViewById returns null. There is no view for id "fab" in the xml.