Question

我正在尝试在活动中使用操作栏实现标签。但我得到一个例外。是什么原因？这是我的代码：
MainActivity.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener {

    SectionsPagerAdapter mSectionsPagerAdapter;
    ViewPager mViewPager;
String arr[]=new String[]{"Vegetables","Drinks","Fruits","Chai","Eatables"};


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

       final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        mSectionsPagerAdapter = new SectionsPagerAdapter(
                getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        mViewPager
                .setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {
                        actionBar.setSelectedNavigationItem(position);
                    }
                });

        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 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) {
        // 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);
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        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.

         String str[]=null;
            for(int i=0;i<10;i++)
                str[i]=arr[position];
            Fragment fragment = new HomeFragment();
           Bundle bundle =new Bundle();
            bundle.putStringArray("air",str);
            fragment.setArguments(bundle);
            return fragment;
        }



        @Override
        public int getCount() {
            // Show 3 total pages.
            return arr.length;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            return arr[position];
        }
    }

}

这是我得到的例外：

08-05 16:12:44.439  10012-10012/com.works.vipul.peppertap3 E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.works.vipul.peppertap3/com.works.vipul.peppertap3.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.works.vipul.peppertap3.MainActivity.onCreate(MainActivity.java:31)
            at android.app.Activity.performCreate(Activity.java:4470)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
08-05 16:12:54.729  10012-10012/com.works.vipul.peppertap3 I/Process﹕ Sending signal. PID: 10012 SIG: 9
08-05 16:14:16.039  10483-10483/com.works.vipul.peppertap3 D/AndroidRuntime﹕ Shutting down VM
08-05 16:14:16.039  10483-10483/com.works.vipul.peppertap3 W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40c1aa68)
08-05 16:14:16.059  10483-10483/com.works.vipul.peppertap3 E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.works.vipul.peppertap3/com.works.vipul.peppertap3.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.works.vipul.peppertap3.MainActivity.onCreate(MainActivity.java:31)
            at android.app.Activity.performCreate(Activity.java:4470)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
08-05 16:14:28.759  10483-10483/com.works.vipul.peppertap3 I/Process﹕ Sending signal. PID: 10483 SIG: 9
08-05 16:15:31.819  10911-10911/com.works.vipul.peppertap3 D/AndroidRuntime﹕ Shutting down VM
08-05 16:15:31.819  10911-10911/com.works.vipul.peppertap3 W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40c1aa68)
08-05 16:15:31.839  10911-10911/com.works.vipul.peppertap3 E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.works.vipul.peppertap3/com.works.vipul.peppertap3.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.works.vipul.peppertap3.MainActivity.onCreate(MainActivity.java:31)
            at android.app.Activity.performCreate(Activity.java:4470)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
            at android.app.ActivityThread.access$600(ActivityThread.java:128)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4517)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
            at dalvik.system.NativeStart.main(Native Method)
08-05 16:15:41.659  10911-10911/com.works.vipul.peppertap3 I/Process﹕ Sending signal. PID: 10911 SIG: 9

这是片段代码：

HomeFragment.java

package com.works.vipul.peppertap3;    
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class HomeFragment extends Fragment {

    public HomeFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main_dummy,
                container, false);
        String arr[]= getArguments().getStringArray("air");
        ListView l=(ListView)rootView.findViewById(R.id.section_label);
        ArrayAdapter a=new ArrayAdapter<String>(getActivity(),android.R.layout.simple_dropdown_item_1line,arr);
        l.setAdapter(a);
        return rootView;
    }
}

这些是布局：
activity_main.xml中

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" />

fragment_main_dummy.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$DummySectionFragment" >

    <ListView
        android:id="@+id/section_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:textSize="25sp" />

</RelativeLayout>

Answer 1

尝试使用：

getSupportActionBar()

而不是：

getActionBar().

你可以这样做：

import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;

public class EntryActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

使用操作栏实现滑动选项卡会给我一个例外

1 个答案: