Android:getActionBar 出现 NullPointerException

Question

我正在实现抽屉导航滑动菜单。在

获取 java.lang.NullPointerException

getActionBar().setDisplayShowHomeEnabled(true);
getActionBar().setHomeButtonEnabled(true);

在我的应用程序中，我尝试了 Activity 扩展 Activity 以及 AppCompatActivity。

这是我的onCreate代码

protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        mTitle = mDrawerTitle = getTitle();

        navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);
        navMenuIcons = getResources().obtainTypedArray(R.array.nav_drawer_icons);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.list_slidermenu);
        navDrawerItems = new ArrayList<NavDrawerItem>();
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1), true, "22"));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1), true, "50+"));
        navMenuIcons.recycle();
        mDrawerList.setOnItemClickListener(new SlideMenuClickListener());
        adapter = new NavDrawerListAdapter(getApplicationContext(), navDrawerItems);
        mDrawerList.setAdapter(adapter);
       //abling action bar app icon and behaving it as toggle button
        getActionBar().setDisplayShowHomeEnabled(true);
        getActionBar().setHomeButtonEnabled(true);
        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,

                R.drawable.menu_left, //nav menu toggle icon
                R.string.app_name, // nav drawer open - description for accessibility
                R.string.app_name // nav drawer close - description for accessibility
        )
        {
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(mTitle);
                // calling onPrepareOptionsMenu() to show action bar icons
                invalidateOptionsMenu();
            }

            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle(mDrawerTitle);
                // calling onPrepareOptionsMenu() to hide action bar icons
                invalidateOptionsMenu();}
        };

        mDrawerLayout.setDrawerListener(mDrawerToggle);
        if (savedInstanceState == null) {
            // on first time display view for first nav item
            displayView(0);
        }
    }

这是 LogCat 信息

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tazeen.slidingmenu/com.example.tazeen.slidingmenu.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.tazeen.slidingmenu.MainActivity.onCreate(MainActivity.java:62)
            at android.app.Activity.performCreate(Activity.java:5008)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
            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)

Answer 1

如果您从 AppCompatActivity 扩展，您应该使用 getSupportActionBar()

如果你扩展Activity，你可以使用getActionBar()，

但在这两种情况下，

您已确保为您的 Activity 分配了支持 ActionBar 的主题。

例如:Theme.AppCompat.Light

或者您可以通过编程方式进行，

requestWindowFeature(Window.FEATURE_ACTION_BAR);

之前

super.onCreate(savedInstanceState);

但最好为您的 Activity 声明和分配样式，而不是以编程方式进行。