Getting null on object reference for Up navigation

Question

This seems to work but not sure if I have to add it to every Activity?

android:theme="@style/Theme.AppCompat"

along with extending the Classes with ActionBarActivity

Here is what I did in the manifest:

<application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.shmira.shmira.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
<activity android:name=".Book"
            android:theme="@style/Theme.AppCompat"
            android:label="Shmira" >
        </activity>

The class looking like this:

public class Book extends ActionBarActivity



 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.book);


        getSupportActionBar().setDisplayHomeAsUpEnabled(true); 



@Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar actions click
        switch (item.getItemId()) {
            // lets user travel back to where they came from
            case android.R.id.home:
                finish();
                return true;

Where you called getActionBar().setDisplayHomeAsUpEnabled(true)? and also apply <activity android:name=".Book" android:theme="@style/Theme.AppCompat" android:label="books"></activity> — M D
– M D, Commented Apr 22, 2015 at 11:59
possible duplicate of Android Error [Attempt to invoke virtual method 'void android.app.ActionBar' on a null object reference] — Yuva Raj
– Yuva Raj, Commented Apr 22, 2015 at 11:59

Musa Y. · Accepted Answer · 2015-04-22 12:43:17Z

1

If you're using a support lib i.e. ActionBarActivity add the following line after calling setContentView:

  getSupportActionBar().setDisplayHomeAsUpEnabled(true);

and if you're not using a support lib i.e. Activity, then simply change getSupportActionBar() to getActionBar().. and don't forget to add android:theme="@style/Theme.AppCompat" to AndroidManifest.xml

To go back to the MainActivity instead of up through the stack, define ActivityA as parent for ActivityB in AndroidManifest.xml like this:

    <activity
        android:name=".Book"
        android:label="Shmira">
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.shmira.shmira.MainActivity" />
    </activity>

edited Apr 22, 2015 at 12:43

answered Apr 22, 2015 at 12:08

Musa Y.

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8 Comments

Lion789 Over a year ago

I have to add that theme to every activity in my manifest? And if I am using ActionBarActivity only on the MainActivity I can still extend only Activity for the other activities? ... I still get the error unless I call the theme you mentioned and then use getSupportAction but I have to then extend ActionBarActivity

Musa Y. Over a year ago

You don't have to.. you can set it once in <application> attribute, for e.g. <application .... android:theme="@style/Theme.AppCompat">. For more info developer.android.com/guide/topics/manifest/…

Musa Y. Over a year ago

Can you explain what does it do now and what is it that you want ?

Lion789 Over a year ago

Ok it works thanks... without the parent apparently I was calling finish on creation of the new activity... so one last question so for every activity I have to add this... android:theme="@style/Theme.AppCompat" and extend ActionBarActivity ... because that is the only way it seems to work... and I have to use the style in each one it seems this is the pastebin of my style.. pastebin.com/S0JWejNg

Musa Y. Over a year ago

Glad it works.. Please accept it as answer if you think my answer helped for the original question.

|

John · Accepted Answer · 2015-04-22 12:42:42Z

0

Try adding ParentActivity of your Activity in AcivityTag in AndroidManifest.xml

 <activity
        android:name=".Book"
        android:label="@string/book"
        android:parentActivityName="ParentActivity">

Try Adding below code in your oncreate

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setDisplayShowHomeEnabled(true);

edited Apr 22, 2015 at 12:42

answered Apr 22, 2015 at 12:19

John

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3 Comments

Lion789 Over a year ago

Look at the edit, I tried that and it works... but not sure if it is right? Since it does not return it to CreateBook but back to the home page

John Over a year ago

Make sure that your parentActivityName should be the one where you started the Book Activity.

Lion789 Over a year ago

I tried that the getActionBar has an error the same as before

Vinoth Kannan · Accepted Answer · 2015-04-22 12:43:17Z

0

getSupportActionBar().setDisplayHomeAsUpEnabled(true);

In your code your using getActionBar() while base class is ActionBarActivity. You should use above code instead.

edited Apr 22, 2015 at 12:43

answered Apr 22, 2015 at 12:04

Vinoth Kannan

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1 Comment

Vinoth Kannan Over a year ago

use getSupportActionBar() for ActionBarActivity

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