我一直在用android学习这个教程，
https://developer.android.com/training/implementing-navigation/lateral.html
我无法在操作栏中添加标签， 我收到错误说
Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference
我在某处读到标签不再受支持了， 我已经决定在同一个教程中使用标题条，但很好，但我更喜欢标签， 我弄错了什么？
这是我的片段活动，
package apps.radwin.wintouch.activities.alignmentActivities;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.GravityCompat;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import apps.radwin.wintouch.R;
import apps.radwin.wintouch.adapters.aligmentAdapters.SwipeAdapterProjectSelection;
public class projectSelectionMainFragment extends FragmentActivity
implements NavigationView.OnNavigationItemSelectedListener {
ViewPager mainViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.project_selection_main_fragment);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
/////////////////////////////////////////
//////// Start Of Implementation ////////
/////////////////////////////////////////
mainViewPager = (ViewPager) findViewById(R.id.projectSelectionMainViewPager); // the main view pager
SwipeAdapterProjectSelection swipeAdapter = new SwipeAdapterProjectSelection(getSupportFragmentManager()); // calls the adapter and initlizes it
mainViewPager.setAdapter(swipeAdapter); // sets the adapter
///////////////////////////////////////////
/////start of action bar implementation////
///////////////////////////////////////////
final ActionBar actionBar = getActionBar();
// Specify that tabs should be displayed in the action bar.
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create a tab listener that is called when the user changes tabs.
ActionBar.TabListener tabListener = new ActionBar.TabListener() {
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
}
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
// hide the given tab
}
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
// probably ignore this event
}
};
// Add 3 tabs, specifying the tab's text and TabListener
for (int i = 0; i < 3; i++) {
actionBar.addTab(
actionBar.newTab()
.setText("Tab " + (i + 1))
.setTabListener(tabListener));
}
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.project_selection_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_camera) {
// Handle the camera action
} else if (id == R.id.nav_gallery) {
} else if (id == R.id.nav_slideshow) {
} else if (id == R.id.nav_manage) {
} else if (id == R.id.nav_share) {
} else if (id == R.id.nav_send) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
错误日志：
Process: apps.radwin.wintouch, PID: 32161
java.lang.RuntimeException: Unable to start activity ComponentInfo{apps.radwin.wintouch/apps.radwin.wintouch.activities.alignmentActivities.projectSelectionMainFragment}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.access$1100(ActivityThread.java:221)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference
at apps.radwin.wintouch.activities.alignmentActivities.projectSelectionMainFragment.onCreate(projectSelectionMainFragment.java:74)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.access$1100(ActivityThread.java:221)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
build gradle：
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.0.3"
defaultConfig {
applicationId "apps.radwin.wintouch"
minSdkVersion 19
targetSdkVersion 23
versionCode 21
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
repositories {
jcenter()
}
dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
testCompile 'junit:junit:4.12'
compile files('libs/core.jar')
provided 'org.glassfish:javax.annotation:10.0-b28'
compile 'com.android.support:appcompat-v7:23.4.0'
compile 'com.android.support:design:23.4.0'
compile 'com.google.android.gms:play-services-appindexing:8.4.0'
compile 'com.github.ybq:Android-SpinKit:1.0.4'
compile 'com.squareup.retrofit2:retrofit:2.0.1'
compile 'com.squareup.retrofit2:converter-gson:2.0.1'
compile 'com.michaelpardo:activeandroid:3.1.0-SNAPSHOT'
compile 'com.rengwuxian.materialedittext:library:2.1.4'
compile 'com.github.fenjuly:ArrowDownloadButton:9e15b85e8a'
compile 'com.oguzdev:CircularFloatingActionMenu:1.0.2'
compile 'com.yayandroid:LocationManager:1.1.1'
compile 'com.google.android.gms:play-services-location:7.5.0'
compile 'com.github.quentin7b:android-location-tracker:3.2'
compile 'com.github.lzyzsd:circleprogress:1.1.0@aar'
compile 'com.android.support:support-v4:23.4.0'
compile 'com.astuetz:pagerslidingtabstrip:1.0.1'
}
答案 0 :(得分：0)
在
final ActionBar actionBar = getActionBar();
组
setSupportActionBar(actionBar);
setSupportActionBar(toolbar);
答案 1 :(得分：0)
您应该延长AppCompatActivity而不是FragmentActivity，因为AppCompatActivity继承自FragmentActivity，您需要将Toolbar设为ActionBar 。还要确保您的基本主题为AppCompat.Light.NoActionBar类似
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
并包含
setSupportActionBar(toolbar);
之后
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
并获取getSupportActionBar();而非getActionBar();
答案 2 :(得分：0)
首先将工具栏设置为操作栏
setSupportActionBar(toolbar);
而不是
final ActionBar actionBar = getActionBar();
请使用
final ActionBar actionBar = getSupportActionBar();
同时确保您提到的inheme / style windowActionBar为true或in activity 。getWindow（）requestFeature（Window.FEATURE_ACTION_BAR）;
答案 3 :(得分：0)
通过删除旧的操作栏实现并插入新的来回答 Tabllayout实现，如android所述，
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabsLayoutWorkorderSelection);
tabLayout.setupWithViewPager(mainViewPager);
因为它是在您在Android中打开新活动时可以执行的新tabbed activity中实现的。
在这种情况下，类可以扩展AppCompatActivity而不是FragmentActivity。