Android 代码不起作用

我正在使用android studio，我正在尝试实现这里提到的代码 但它不起作用。我正在尝试用标签和片段设置操作栏。但每次我尝试运行应用程序时都会崩溃。我的代码如下

main活动

public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Notice that setContentView() is not used, because we use the root
    // android.R.id.content as the container for each fragment

    // setup action bar for tabs
    ActionBar actionBar = getActionBar();

    actionBar.setDisplayShowTitleEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    Tab tab = actionBar.newTab()
            .setText(R.string.artist)
            .setTabListener(new TabListener<keyPad>(
                    this, "artist", keyPad.class));
    actionBar.addTab(tab);

    tab = actionBar.newTab()
            .setText(R.string.album)
            .setTabListener(new TabListener<CallLog>(
                    this, "album",CallLog.class));
    actionBar.addTab(tab);
}

活动\u main.xml:

  <?xml version="1.0" encoding="utf-8"?>
  <manifest
     xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.example.iahmed.actionbarandroidstudio" >

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:theme="@style/AppTheme"

    android:label="@string/app_name">
    <activity
        android:name="MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
       </activity>
   </application>

 </manifest>

   import android.app.ActionBar;
   import android.app.Activity;
   import android.app.Fragment;
   import android.app.FragmentTransaction;
   import android.os.Bundle;
   import android.widget.Toast;

   public  class TabListener<T extends Fragment> implements   ActionBar.TabListener {
private final Activity mActivity;
private final String mTag;
private final Class<T> mClass;
private final Bundle mArgs;
private Fragment mFragment;

public TabListener(Activity activity, String tag, Class<T> clz) {
    this(activity, tag, clz, null);
}

public TabListener(Activity activity, String tag, Class<T> clz, Bundle args) {
    mActivity = activity;
    mTag = tag;
    mClass = clz;
    mArgs = args;


    mFragment = mActivity.getFragmentManager().findFragmentByTag(mTag);
    if (mFragment != null && !mFragment.isDetached()) {
        FragmentTransaction ft = mActivity.getFragmentManager().beginTransaction();
        ft.detach(mFragment);
        ft.commit();
    }
}

public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
    if (mFragment == null) {
        mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
        ft.add(android.R.id.content, mFragment, mTag);
    } else {
        ft.attach(mFragment);
    }
}

public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
    if (mFragment != null) {
        ft.detach(mFragment);
    }
}

public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
    Toast.makeText(mActivity, "Reselected!", Toast.LENGTH_SHORT).show();
}
}

<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="wrap_content" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

（原木类别的一部分）

---

用于添加操作栏的活动的代码中缺少setContentView（）。

请使用

getSupportActionBar（）

而不是

getActionBar（）

格式化代码，因为您继承自

AppCompatActivity

。完成请参见@Der GolemgetSupportActionbar在sdk 15中不起作用@Gaëtan如果您不添加支持库，则它不起作用。但在使用根的示例中，setContentView（）不可用。如果它是根，则活动需要布局来显示视图。

public class keyPad extends Fragment {

@Override

public View onCreateView(LayoutInflater inflater, ViewGroup container,

                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.keypad, container, false);

    return rootView;

}
}

<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="wrap_content" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

   06-09 13:01:04.647    4775-4775/com.example.iahmed.actionbarandroidstudio E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.iahmed.actionbarandroidstudio/com.example.iahmed.actionbarandroidstudio.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
        at android.app.ActivityThread.access$600(ActivityThread.java:130)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4745)
        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:786)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.example.iahmed.actionbarandroidstudio.MainActivity.onCreate(MainActivity.java:26)
        at android.app.Activity.performCreate(Activity.java:5008)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)