NullPointerException with android.support.v7.widget.Toolbar

Question

I am currently trying to implement a navigation drawer in my app. I am having an issue with the Toolbar being null. I have done many searches online and tried many different solutions to no avail. I have not finished writing all the code but I can't launch my app to check the navigation drawer. Can anyone see where I went wrong?

If there is anything else I need to post, let me know.

I included this on all my activity screens

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

app_bar.xml

<?xml version="1.0" encoding="utf-8"?> <android.support.v7.widget.Toolbar    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:minHeight="?attr/actionBarSize"    android:background="?attr/colorPrimary"    app:popupTheme="@style/ThemeOverlay.AppCompat.Dark" > </android.support.v7.widget.Toolbar> 

line 72 of MainActivity

setSupportActionBar(mToolbar); 

Main Activity

public class Trans_List extends ActionBarActivity {   private Toolbar mToolbar;   private CharSequence mTitle;      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);         setContentView(R.layout.activity_trans_list);          mToolbar = (Toolbar) findViewById(R.id.app_bar);          setSupportActionBar(mToolbar);         getSupportActionBar().setDisplayShowHomeEnabled(true);         NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)                 getSupportFragmentManager().findFragmentById(R.id.left_drawer);         drawerFragment.setUp((DrawerLayout) findViewById(R.id.drawer_layout), mToolbar); 

Style.xml

<?xml version="1.0" encoding="utf-8"?> <resources>     <style name="AppBaseTheme" parent="@style/Theme.AppCompat.Light.DarkActionBar" >         <item name="windowActionBar">false</item>     </style>      <style name="Theme.split" parent="AppBaseTheme">      </style>      <style name="dialog_custom" parent="@style/Theme.AppCompat.Dialog">         <item name="@android:listPreferredItemPaddingLeft">20dip</item>         <item name="@android:listPreferredItemPaddingRight">20dip</item>         <item name="@android:listPreferredItemPaddingStart">20dip</item>         <item name="@android:listPreferredItemPaddingEnd">20dip</item>     </style> </resources> 

LogCat

01-07 01:14:29.702    4811-4811/com.lee.yuchan.splt E/AndroidRuntime﹕ FATAL EXCEPTION: main         Process: com.lee.yuchan.splt, PID: 4811         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lee.yuchan.splt/com.lee.yuchan.splt.Trans_List}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' 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 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference                 at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:95)                 at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:88)                 at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:84)                 at android.support.v7.app.ActionBarActivityDelegateBase.setSupportActionBar(ActionBarActivityDelegateBase.java:175)                 at android.support.v7.app.ActionBarActivity.setSupportActionBar(ActionBarActivity.java:92)                 at com.lee.yuchan.splt.Trans_List.onCreate(Trans_List.java:72)                 at android.app.Activity.performCreate(Activity.java:5933)                 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)                 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) 

Main Activity XML

 <?xml version="1.0" encoding="utf-8"?>      <android.support.v4.widget.DrawerLayout         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:id="@+id/drawer_layout"         android:layout_width="match_parent"         android:layout_height="match_parent">         <!-- The main content view -->     <LinearLayout     android:layout_width="match_parent"     android:layout_height="match_parent"     android:orientation="vertical">          <include             layout="@layout/app_bar"/>          <TextView             android:id="@+id/selectItems"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:text="@string/select_instr1"             android:textSize="20sp"             android:gravity="center"             android:paddingTop="4sp"             android:paddingBottom="10sp" >         </TextView>          <ListView             android:id="@+id/listView1"             android:layout_width="match_parent"             android:layout_height="0dip"             android:layout_weight="1" >         </ListView>          <Button             android:id="@+id/buttonChecked"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:layout_margin="0dip"             android:background="@drawable/custom_button"             android:textColor="#ffffff"             android:text="@string/next_button" />      </LinearLayout>      <!-- The navigation drawer -->     <fragment         android:id="@+id/left_drawer"         android:layout_width="@dimen/nav_dr"         android:layout_height="match_parent"         android:layout_gravity="start"         app:layout="@layout/fragment_navigation_drawer"         android:name="com.lee.yuchan.splt.NavigationDrawerFragment"         tools:layout="@layout/fragment_navigation_drawer" />      </android.support.v4.widget.DrawerLayout> 

Answer 1

Set the id attribute in the Toolbar xml like this:

<?xml version="1.0" encoding="utf-8"?> <android.support.v7.widget.Toolbar     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:app="http://schemas.android.com/apk/res-auto"     android:id="@+id/app_bar"     app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:minHeight="?attr/actionBarSize"     android:background="?attr/colorPrimary"     app:popupTheme="@style/ThemeOverlay.AppCompat.Dark" > </android.support.v7.widget.Toolbar> 

Then remove it from the include block so it looks like this:

<include     layout="@layout/app_bar"/> 

And to simplify further you could just remove the include block completely and simply insert the Toolbar directly into the xml where the include was.