NullPointerException: with ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
Solution 1
The cause of your issue is using MainActivity extend Activity
with support theme style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"
. It's incompatible things.
Which min sdk you need?
In your code having MainActivity extends Activity
you don't need AppCompatTheme
. Use name="AppTheme" parent="android:Theme.Light
"
If you are using Theme.AppCompat.Light.DarkActionBar
, you should extend your Activity
from AppCompatActivity
, and use getSupportActionBar()
.
Instead of:
public class MainActivity extends Activity {
use:
public class MainActivity extends AppCompatActivity {
and instead of:
getActionBar().setTitle(mTitles);
use:
getSupportActionBar().setTitle(mTitles);
Solution 2
This problem might be caused by your theme. Check it again, and make sure that it parent with Theme.AppCompat.Light.DarkActionBar
.
<style name="MyTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="android:windowNoTitle">true</item>
<item name="windowActionBar">true</item>
...
</style>
If your activity extends AppCompatActivity
or ActionBarActivity
, call getSupportActionBar()
.
Solution 3
Put assert getActionBar () != null;
after mActionBar = getActionBar();
![Vasilisfoo](https://i.stack.imgur.com/HC7Ko.jpg?s=256&g=1)
Vasilisfoo
Master in Computer science - Android dev, nodejs , mongodDB- learning Swift
Updated on May 16, 2020Comments
-
Vasilisfoo about 4 years
I get this nullPointerException on runtime:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
code from mainActivity:
package com.example.vasilis.spangreek; import android.app.ActionBar; import android.app.Activity; import android.content.res.Configuration; import android.content.res.TypedArray; import android.os.Bundle; import android.support.v4.widget.DrawerLayout; import android.support.v7.app.ActionBarDrawerToggle; import android.support.v7.app.AppCompatActivity; import android.util.DisplayMetrics; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.ExpandableListView; import java.util.ArrayList; import java.util.LinkedHashMap; import java.util.List; import java.util.Map; import adapter.ExpandableListViewAdapter; import model.NavDrawerItem; public class MainActivity extends Activity { private DrawerLayout mDrawerLayout; private ExpandableListView mExpandableListView; private ActionBarDrawerToggle mActionBarDrawerToggle; //nav drawer Title private CharSequence mDrawerTitle; //used to store app titles private CharSequence mTitles; //slide menu items private String[] navMenuItems; private String[] navSubMenuItems; private TypedArray navMenuIcons; private List<NavDrawerItem> groupList; private List<NavDrawerItem> childList; private Map<NavDrawerItem, List<NavDrawerItem>> mapList; private ExpandableListViewAdapter mAdapter; ActionBar mActionBar; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mTitles = mDrawerTitle = getTitle(); //nav drawer icons navMenuIcons = getResources().obtainTypedArray(R.array.nav_icons); mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer_layout); createGroupList(); CreateChildList(); // Recycle the typed array navMenuIcons.recycle(); mExpandableListView = (ExpandableListView)findViewById(R.id.list_slideMenu); mAdapter = new ExpandableListViewAdapter(this, mapList, groupList); mExpandableListView.setAdapter(mAdapter); mActionBar = getActionBar(); // enabling action bar app icon and behaving it as toggle button mActionBar.setDisplayHomeAsUpEnabled(true); mActionBar.setHomeButtonEnabled(true); //toggle mActionBarDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.app_name, R.string.app_name) { public void onDrawerClosed(View drawerView) { mActionBar.setTitle(mDrawerTitle); // calling onPrepareOptionsMenu() to hide action bar icons invalidateOptionsMenu(); } public void onDrawerOpened(View drawerView) { mActionBar.setTitle(mDrawerTitle); // calling onPrepareOptionsMenu() to hide action bar icons invalidateOptionsMenu(); } }; mActionBarDrawerToggle.setHomeAsUpIndicator(R.drawable.ic_drawer); mDrawerLayout.setDrawerListener(mActionBarDrawerToggle); if(savedInstanceState == null) { //displayView(0); } } /*** * Called when invalidateOptionsMenu() is triggered */ @Override public boolean onPrepareOptionsMenu(Menu menu) { // if nav drawer is opened, hide the action items boolean drawerOpen = mDrawerLayout.isDrawerOpen(mExpandableListView); menu.findItem(R.id.action_settings).setVisible(!drawerOpen); return super.onPrepareOptionsMenu(menu); } @Override public void setTitle(CharSequence title) { mTitles = title; getActionBar().setTitle(mTitles); } /** * When using the ActionBarDrawerToggle, you must call it during * onPostCreate() and onConfigurationChanged()... */ @Override protected void onPostCreate(Bundle savedInstanceState) { super.onPostCreate(savedInstanceState); // Sync the toggle state after onRestoreInstanceState has occurred. mActionBarDrawerToggle.syncState(); } @Override public void onConfigurationChanged(Configuration newConfig) { super.onConfigurationChanged(newConfig); // Pass any configuration change to the drawer toggls mActionBarDrawerToggle .onConfigurationChanged(newConfig); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // toggle nav drawer on selecting action bar app icon/title if (mActionBarDrawerToggle.onOptionsItemSelected(item)) { return true; } // Handle action bar actions click switch (item.getItemId()) { case R.id.action_settings: return true; default: return super.onOptionsItemSelected(item); } } private void createGroupList() { //load slide menu items navMenuItems = getResources().getStringArray(R.array.nav_items); groupList =new ArrayList<NavDrawerItem>(); for (int i = 0 ; i < navMenuItems.length ; i++ ) { groupList.add(i , new NavDrawerItem(navMenuItems[i], navMenuIcons.getResourceId(i, -1))); } } private void CreateChildList() { mapList = new LinkedHashMap<NavDrawerItem, List<NavDrawerItem>>(); navSubMenuItems = getResources().getStringArray(R.array.nav_sub_items); childList = new ArrayList<>(); for ( NavDrawerItem item : groupList) { if(item.getTitle().equalsIgnoreCase("learning Spanish")) { for (int i = 0 ; i < navSubMenuItems.length ; i ++) { childList.add(i, new NavDrawerItem(navSubMenuItems[i])); } } mapList.put(item,childList); } } private void setGroupIndicatorToRight() { /* Get the screen width */ DisplayMetrics dm = new DisplayMetrics(); getWindowManager().getDefaultDisplay().getMetrics(dm); int width = dm.widthPixels; mExpandableListView.setIndicatorBounds(width - getDipsFromPixel(35), width - getDipsFromPixel(5)); } // Convert pixel to dip public int getDipsFromPixel(float pixels) { // Get the screen's density scale final float scale = getResources().getDisplayMetrics().density; // Convert the dps to pixels, based on density scale return (int) (pixels * scale + 0.5f); } }
the lines of code that have problem are :
mActionBar = getActionBar(); // enabling action bar app icon and behaving it as toggle button mActionBar.setDisplayHomeAsUpEnabled(true); mActionBar.setHomeButtonEnabled(true);
i use : style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"
I have used the getSupportActionBar() but i haven't fount any solution
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Jake Lee about 8 yearsAdding a null check hardly fixes the issue?
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Erik over 7 yearsI had the null pointer issue using
getSupportActionBar()
. My issue was fixed by adding<item name="windowActionBar">true</item>
in my styles.xml.