java - Android java.lang.NullPointerException getActionBar()

Question

我尝试实现一个设置 Activity 类，但它给了我一个错误:

Caused by: java.lang.NullPointerException
            at com.example.andrei.sunshine.SettingsActivity.setupActionBar(SettingsActivity.java:58)
            at com.example.andrei.sunshine.SettingsActivity.onCreate(SettingsActivity.java:48)
            at android.app.Activity.performCreate(Activity.java:5264)

这是行:getActionBar().setDisplayHomeAsUpEnabled(true);

AndroidManifest 是:

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <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>
    <activity
        android:name=".DetailActivity"
        android:label="@string/title_activity_detail"
        android:parentActivityName=".MainActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.andrei.sunshine.MainActivity" />
    </activity>
    <activity
        android:name=".SettingsActivity"
        android:label="@string/title_activity_settings"
        android:parentActivityName=".MainActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.andrei.sunshine.MainActivity" />
    </activity>
</application>

请帮助我

Answer 1

如果您的SettingsActivity扩展ActionBarActivity，您的getActionBar();将可用。

public class SettingsActivity extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.yourLayout);
        //If you use support library
        //getSupportActionBar().setDisplayHomeAsUpEnabled(true); 
        getActionBar().setDisplayHomeAsUpEnabled(true);
    }
}

请参阅documentation了解更多信息。