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 `` — M D, Apr 22 '15 at 11:59
possible duplicate of [Android Error \[Attempt to invoke virtual method 'void android.app.ActionBar' on a null object reference\]](http://stackoverflow.com/questions/28144657/android-error-attempt-to-invoke-virtual-method-void-android-app-actionbar-on) — Yuva Raj, Apr 22 '15 at 11:59

Musa Y. · Accepted Answer · 2015-04-22T12:43:17.960

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 '15 at 12:43

answered Apr 22 '15 at 12:08

Musa Y.

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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 – Lion789 Apr 22 '15 at 12:15
You don't have to.. you can set it once in `` attribute, for e.g. ``. For more info http://developer.android.com/guide/topics/manifest/application-element.html – Musa Y. Apr 22 '15 at 12:19
Can you explain what does it do now and what is it that you want ? – Musa Y. Apr 22 '15 at 12:58
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.. http://pastebin.com/S0JWejNg – Lion789 Apr 22 '15 at 13:09
Glad it works.. Please accept it as answer if you think my answer helped for the original question. – Musa Y. Apr 22 '15 at 13:12
Just noticed your last question... You don't have to set a theme for every activity unless you want all/some activities to have different themes, if you set the theme in `` that's sufficient and will apply that theme in all activities. – Musa Y. Apr 22 '15 at 13:20
I know I tried setting it in the application but it errors me afterwards... but I do have to extend every class with ActionBarActivity then? – Lion789 Apr 22 '15 at 13:22
Yes, to apply themes you need to have xml file in your activity and extend every class with ActionBarActivity.. otherwise, it won't work. – Musa Y. Apr 22 '15 at 14:02

Vinoth Kannan · Answer 2 · 2015-04-22T12:43:17.243

0

getSupportActionBar().setDisplayHomeAsUpEnabled(true);

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

edited Apr 22 '15 at 12:43

answered Apr 22 '15 at 12:04

Vinoth Kannan

242
5
16

use getSupportActionBar() for ActionBarActivity – Vinoth Kannan Apr 22 '15 at 12:43

John · Answer 3 · 2015-04-22T12:42:42.677

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 '15 at 12:42

answered Apr 22 '15 at 12:19

John

8,846
8
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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 – Lion789 Apr 22 '15 at 12:23
Make sure that your parentActivityName should be the one where you started the Book Activity. – John Apr 22 '15 at 12:33
I tried that the getActionBar has an error the same as before – Lion789 Apr 22 '15 at 12:38

Getting null on object reference for Up navigation

3 Answers3