Android:getSupportActionBar()始终在ActionBarSherlock库中返回null

Question

我正在尝试使用ActionBarSherlock库来为我的Android应用程序中的选项卡提供向后兼容的ActionBar支持,因此我下载了最新版本,构建了演示并运行它.

如果你去Action Bar,然后选择Tab Navigation,它每次都会崩溃.这是堆栈跟踪:

09-03 02:34:47.940: ERROR/AndroidRuntime(3078): FATAL EXCEPTION: main  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.actionbarsherlock.sample.demos/com.actionbarsherlock.sample.demos.app.ActionBarTabNavigation}: java.lang.NullPointerException  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1748)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1764)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread.access$1500(ActivityThread.java:122)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1002)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.os.Handler.dispatchMessage(Handler.java:99)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.os.Looper.loop(Looper.java:132)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread.main(ActivityThread.java:4025)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at java.lang.reflect.Method.invokeNative(Native Method)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at java.lang.reflect.Method.invoke(Method.java:491)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at dalvik.system.NativeStart.main(Native Method)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): Caused by: java.lang.NullPointerException  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at com.actionbarsherlock.sample.demos.app.ActionBarTabNavigation.onCreate(ActionBarTabNavigation.java:19)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1712)  
09-03 02:34:47.940: ERROR/AndroidRuntime(3078): ... 11 more  

在修复此问题之前,我无法继续使用我的应用.我编写了一堆代码,在我的应用程序中设置了操作栏,并尝试运行它,并且由于getSupportActionBar()调用的返回值为null而导致NPE崩溃.

相关代码实际上是在库的演示中:

public class ActionBarTabNavigation extends FragmentActivity implements ActionBar.TabListener {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        getSupportFragmentManager()
            .beginTransaction()
            .add(android.R.id.content, FragmentStackSupport.CountingFragment.newInstance(0))
            .commit();

        getSupportActionBar().setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        for (int i = 0; i < 3; i++) {
            ActionBar.Tab tab = getSupportActionBar().newTab();
            tab.setText("Tab " + i);
            tab.setTabListener(this);
            getSupportActionBar().addTab(tab);
        }
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        getSupportFragmentManager()
            .beginTransaction()
            .replace(android.R.id.content, FragmentStackSupport.CountingFragment.newInstance(tab.getPosition()))
            .commit();
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
    }
}

Answer 1

您应该将Sherlock主题添加到您的应用程序中

<application android:icon="@drawable/icon" android:label="@string/app_name"
        android:debuggable="false" android:theme="@style/Theme.Sherlock">

Answer 2

我在Android ICS 4.0.4上遇到了同样的问题.我正在使用requestWindowFeature(Window.FEATURE_NO_TITLE);FragmentActivity,但这是将ActionBar隐藏在ICS +设备上,导致它getSupportActionBar()为null.

只需删除:
requestWindowFeature(Window.FEATURE_NO_TITLE);

它就像一个魅力.

希望它可以帮助某人.

Answer 3

在Honeycomb +设备上发生这种情况的另一个原因是因为windowNoTitle属性是按照您的风格设置的.摆脱它,因为ActionBarSherlock会自动将它移除到预蜂窝设备中.

Answer 4

您可能从null中获取null的另一个原因getSupportActionBar()是尝试setContentView(R.layout.main)在添加片段之前或之后调用它.

我重构了oncreate并错误地放了getSupportActionBar().setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);以后super.onCreate(savedInstanceState);

Answer 5

这是一个有趣的:不要将主题设置为 -

    android:theme="@style/Theme.NoActionbar"

Answer 6

您可能获得null的另一个原因getSupportActionBar()是在Honeycomb +上的TabHost中使用该活动时.

Answer 7

根据你的写出代码的方式.确保在调用之前先设置了工具栏.

  mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);