setSupportActionBar() throws Nullpointer exception

Question

I am new to android and i was following following tutorial for Material Design Toolbar :

http://www.android4devs.com/2014/12/how-to-make-material-design-app.         


        

Answer 1

You need to call setContentView BEFORE adding any Views such as the Toolbar.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);         // <-- call this first

    toolbar = (Toolbar) findViewById(R.id.toolbar); // <-- setup views after

    setSupportActionBar(toolbar);
    setTitle("DDIT_Results");
}

Please see the Official Android Developers blog here: http://android-developers.blogspot.com/2014/10/appcompat-v21-material-design-for-pre.html

Action Bar

To use Toolbar as an Action Bar, first disable the decor-provided Action Bar. The easiest way is to have your theme extend from Theme.AppCompat.NoActionBar (or its light variant).

Second, create a Toolbar instance, usually via your layout XML:

<android.support.v7.widget.Toolbar
    android:id=”@+id/my_awesome_toolbar”
    android:layout_height=”wrap_content”
    android:layout_width=”match_parent”
    android:minHeight=”?attr/actionBarSize”
    android:background=”?attr/colorPrimary” />

The height, width, background, and so on are totally up to you; these are just good examples. As Toolbar is just a ViewGroup, you can style and position it however you want.

Then in your Activity or Fragment, set the Toolbar to act as your Action Bar:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.blah);

    final Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
    setSupportActionBar(toolbar);
}

From this point on, all menu items are displayed in your Toolbar, populated via the standard options menu callbacks.

Answer 2

Before adding toolbar you need to remove action from your style like

 <style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
        <item name="android:windowActionBar">false</item>
        <item name="android:windowNoTitle">true</item>
    </style>

Now define toolbar in res/xml/toolbar.xml

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

Now include this toolbar in our activity layout xml like

<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">

    <include
        android:id="@+id/tool_bar"
        layout="@xml/toolbar" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

Note : Now while defining toolbar in activity we will use "tool_bar" as id not "appbar" id

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar actionbar = (Toolbar) findViewById(R.id.tool_bar);
        setSupportActionBar(actionbar);
    }
}

Now you can see in your activity toolbar

Answer 3

just import

android.support.v7.widget.Toolbar;

not

android.widget.Toolbar;

Answer 4

Make sure to add theme in the activity inside manifests

 <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

then define this attributes to the theme used above in the style.xml

 <style name="AppTheme.NoActionBar">
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>

G