I have imported an Android sample project called HorizontalPaging in Android Studio and it works fine when I run it. But when I copied the code into my code, I get a NULL pointer exception in getActionBar().
I have been reading about these problems the whole day but can't get it working. Tried copying the entire code from the sample's MainActivity into my project but no improvements so I am guessing that the problem is in some other file like manifest,styles,etc.
MainActivity.java copied from the sample project
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.Locale;
public class View_Tabs extends FragmentActivity implements ActionBar.TabListener {
SectionsPagerAdapter mSectionsPagerAdapter;
ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Load the UI from res/layout/activity_main.xml
setContentView(R.layout.view_tabs);
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create the adapter that will return a fragment for each of the three primary sections
// of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
// When swiping between different sections, select the corresponding tab. We can also use
// ActionBar.Tab#select() to do this if we have a reference to the Tab.
mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by the adapter. Also
// specify this Activity object, which implements the TabListener interface, as the
// callback (listener) for when this tab is selected.
actionBar.addTab(
actionBar.newTab()
.setText(mSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
// When the given tab is selected, tell the ViewPager to switch to the corresponding page.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment = new DummySectionFragment();
Bundle args = new Bundle();
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.tab_list).toUpperCase(l);
case 1:
return getString(R.string.tab_map).toUpperCase(l);
case 2:
return getString(R.string.tab_list).toUpperCase(l);
}
return null;
}
}
/**
* A dummy fragment representing a section of the app, but that simply displays dummy text.
* This would be replaced with your application's content.
*/
public static class DummySectionFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
public static final String ARG_SECTION_NUMBER = "section_number";
public DummySectionFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.list_tab_fragment, container, false);
TextView dummyTextView = (TextView) rootView.findViewById(R.id.section_label);
dummyTextView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}
}
my manifest
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<!-- TABS: While ViewPager will work on API 4 or above, tabs require an ActionBar. ActionBar is only
available in API 11 or above. -->
<!-- Min/target SDK versions (<uses-sdk>) managed by build.gradle -->
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<meta-data android:name="com.google.android.gms.version"
android:value="@integer/google_play_services_version" />
<!--
<meta-data android:name="com.google.android.gms.version"
android:value="@integer/google_play_services_version" />
-->
<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="xxxxx"/>
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:screenOrientation="portrait"
>
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
....
<activity
android:name=".View_Tabs"
android:label="@string/app_name"
android:screenOrientation="portrait"
>
</activity>
</application>
my styles.xml
<resources>
<!-- Base application theme. -->
<!-- BEFORE <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"> -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="android:windowActionBar">true</item>
</style>
<style name="Theme.Base" parent="android:Theme.Light" />
</resources>
my gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 21
buildToolsVersion "21.1.2"
defaultConfig {
applicationId "xxxx"
minSdkVersion 14
targetSdkVersion 21
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:21.0.3'
compile 'com.google.android.gms:play-services:6.5.87'
//compile 'com.google.android.gms:play-services:7.0.0'
compile files('lib/gson-2.3.jar')
}
