All geek questions in one place

Android FragmentActivity returns null in getActionBar ()

I 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 read about these issues all day, but I can't get it to work. I tried copying all the code from the MainActivity sample to my project, but no improvement, so I assume that the problem is in some other file, such as 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 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') }
+6
source share
2 answers

You must extend an ActionBarActivity instead of a FragmentActivity to have an Actionbar with fragments.

If you use the appcompat v7 library, your activity should extend ActionBarActivity, which is a subclass of FragmentActivity (for more information, see "Adding an action bar").

However, you can try this,

 ActionBar actionBar = (ActionBarActivity)getActivity().getSupportActionBar();

You can find more information here. http://developer.android.com/training/basics/fragments/creating.html

+8
source

getActionBar () will return the correct value only if you have activity with a header. Make sure you set a topic with a headline for your activity in the manifest file.

+1
source

Source: https://habr.com/ru/post/984996/

More articles:


All Articles