java - 带有 NewsReader 演示项目的 actionbar NullPointerException

Question

我尝试使用 NewsReader为我正在处理的事情派生代码，但我遇到了操作栏的问题。所以我决定完全重新创建 NewsReader 代码(对包名称等进行合理编辑)，但我仍然遇到了同样的问题。

我在这个调用中遇到了一个错误:

 setUpActionBar(mIsDualPane, catIndex);

因为这一行:

 actionBar.setDisplayShowTitleEnabled(false);

完整方法:

public void setUpActionBar(boolean showTabs, int selTab) {
    if (Build.VERSION.SDK_INT < 11) {
        // No action bar for you!
        // But do not despair. In this case the layout includes a bar across the
        // top that looks and feels like an action bar, but is made up of regular views.
        return;
    }
    android.app.ActionBar actionBar = getActionBar();
    actionBar.setDisplayShowTitleEnabled(false);
    // Set up a CompatActionBarNavHandler to deliver us the Action Bar nagivation events
    CompatActionBarNavHandler handler = new CompatActionBarNavHandler(this);
    if (showTabs) {
        actionBar.setNavigationMode(android.app.ActionBar.NAVIGATION_MODE_TABS);
        int i;
        for (i = 0; i < CATEGORIES.length; i++) {
            actionBar.addTab(actionBar.newTab().setText(CATEGORIES[i]).setTabListener(handler));
        }
        actionBar.setSelectedNavigationItem(selTab);
    }
    else {
        actionBar.setNavigationMode(android.app.ActionBar.NAVIGATION_MODE_LIST);
        SpinnerAdapter adap = new ArrayAdapter<String>(this, R.layout.actionbar_list_item,
                CATEGORIES);
        actionBar.setListNavigationCallbacks(adap, handler);
    }
    // Show logo instead of icon+title.
    actionBar.setDisplayUseLogoEnabled(true);
}

似乎一些 actionBar 的东西也被弃用了，所以这可能是问题的一部分。我该如何修复/更新此问题？

堆栈跟踪:

06-16 09:24:21.211 24376-24376/com.anothergamedesigner.newsreader E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.anothergamedesigner.newsreader, PID: 24376
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.anothergamedesigner.newsreader/com.anothergamedesigner.newsreader.NewsReaderActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayShowTitleEnabled(boolean)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
    at android.app.ActivityThread.access$1100(ActivityThread.java:222)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:158)
    at android.app.ActivityThread.main(ActivityThread.java:7229)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayShowTitleEnabled(boolean)' on a null object reference
    at com.anothergamedesigner.newsreader.NewsReaderActivity.setUpActionBar(NewsReaderActivity.java:119)
    at com.anothergamedesigner.newsreader.NewsReaderActivity.onCreate(NewsReaderActivity.java:81)
    at android.app.Activity.performCreate(Activity.java:6876)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350) 
    at android.app.ActivityThread.access$1100(ActivityThread.java:222) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:158) 
    at android.app.ActivityThread.main(ActivityThread.java:7229) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

改变

android.app.ActionBar actionBar = getActionBar();

到

ActionBar actionBar = getSupportActionBar();

编辑:

您还需要编辑 styles.xml 和 AndroidManifest.xml。

在您的 styles.xml 中，更改

<style name="NewsReaderStyle" parent="android:Theme.Light.NoTitleBar">

到

<style name="NewsReaderStyle" parent="android:Theme.Light.DarkActionBar">

然后在您的 AndroidManifest.xml 中，更改

android:theme="@style/NewsReaderStyle_NoActionBar"

到

android:theme="@style/NewsReaderStyle"

AppCompat 样式:

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

<style name="NoActionBarTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <!-- Customize your theme here. -->
</style>

现在将 android:theme="@style/AppTheme"添加到您的 list 中。