java - Android ActionBar 不可见

Question

我已经更新了 API 21、工具和附加功能，一些项目中的 ActionBar 已经不可见了。我执行了以下代码，但应用程序崩溃并显示 NullPointerException。

ActionBar actionBar = getActionBar();
actionBar.show();

Logcat 输出

02-23 18:03:36.269: E/AndroidRuntime(3327): FATAL EXCEPTION: main 02-23 18:03:36.269: E/AndroidRuntime(3327): Process: com.example.twaapp, PID: 3327 02-23 18:03:36.269: E/AndroidRuntime(3327): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.twaapp/com.example.twaapp.MainActivity}: java.lang.NullPointerException 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread.access$800(ActivityThread.java:139) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.os.Handler.dispatchMessage(Handler.java:102) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.os.Looper.loop(Looper.java:136) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread.main(ActivityThread.java:5086) 02-23 18:03:36.269: E/AndroidRuntime(3327): at java.lang.reflect.Method.invokeNative(Native Method) 02-23 18:03:36.269: E/AndroidRuntime(3327): at java.lang.reflect.Method.invoke(Method.java:515) 02-23 18:03:36.269: E/AndroidRuntime(3327): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 02-23 18:03:36.269: E/AndroidRuntime(3327): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 02-23 18:03:36.269: E/AndroidRuntime(3327): at dalvik.system.NativeStart.main(Native Method) 02-23 18:03:36.269: E/AndroidRuntime(3327): Caused by: java.lang.NullPointerException 02-23 18:03:36.269: E/AndroidRuntime(3327): at com.example.twaapp.MainActivity.onCreate(MainActivity.java:82) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.Activity.performCreate(Activity.java:5248) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110) 02-23 18:03:36.269: E/AndroidRuntime(3327): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162) 02-23 18:03:36.269: E/AndroidRuntime(3327): ... 11 more

如何让AB可见？

Answer 1

您的 Activity 类应该像这样扩展:

public class MainActivity extends ActionBarActivity{

    ....

}

代替

public class MainActivity extends FragmentActivity{

    ....

}

另外，你需要打电话

ActionBar = getSupportActionBar();

代替

ActionBar = getActionBar();

试试这个。这会起作用。