android - 设置 ViewPager 时出现 PagerSlidingTabStrip NullPointerException

Question

我正在尝试实现 PagerSlidingTabStrip在我的应用程序中。我做了我应该做的一切:

将其添加到我的 XML 中:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<android.support.v4.view.ViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<com.astuetz.PagerSlidingTabStrip
    android:id="@+id/slidingTabs"
    android:layout_width="match_parent"
    android:layout_height="48dip" />

</RelativeLayout>

创建了 PagerSlidingTabStrip 并尝试设置 ViewPager:

PagerSlidingTabStrip slidingTabStrip = (PagerSlidingTabStrip) findViewById(R.id.slidingTabs);
slidingTabStrip.setViewPager(vPager);

但是当我运行应用程序时，它崩溃了，这是 logcat 输出:

04-17 20:56:55.956: E/AndroidRuntime(1587): FATAL EXCEPTION: main
04-17 20:56:55.956: E/AndroidRuntime(1587): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.matejhacin.beautifulvoicerecorder/com.matejhacin.beautifulvoicerecorder.MainActivity}: java.lang.NullPointerException
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.os.Looper.loop(Looper.java:137)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread.main(ActivityThread.java:5103)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at java.lang.reflect.Method.invokeNative(Native Method)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at java.lang.reflect.Method.invoke(Method.java:525)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at dalvik.system.NativeStart.main(Native Method)
04-17 20:56:55.956: E/AndroidRuntime(1587): Caused by: java.lang.NullPointerException
04-17 20:56:55.956: E/AndroidRuntime(1587):     at com.astuetz.PagerSlidingTabStrip.notifyDataSetChanged(PagerSlidingTabStrip.java:200)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at com.astuetz.PagerSlidingTabStrip.setViewPager(PagerSlidingTabStrip.java:182)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at com.matejhacin.beautifulvoicerecorder.MainActivity.onCreate(MainActivity.java:39)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.Activity.performCreate(Activity.java:5133)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-17 20:56:55.956: E/AndroidRuntime(1587):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)

Answer 1

此库中的错误处理不当。如果查看 PagerAdapter 的源代码，您会看到一个方法 getPageTitle: https://github.com/android/platform_frameworks_support/blob/master/v4/java/android/support/v4/view/PagerAdapter.java#L306-Lundefined

请注意，默认情况下它返回 null。这就是您看到空指针异常的原因。解决方案是在您的 PagerAdapter 实现中覆盖此方法

@Override
public CharSequence getPageTitle(int position) {
  // return the title of the tab
}

如果您实际上不需要字符串标题，并且希望选项卡使用自定义 View ，例如图像，那么您的 PagerAdapter 必须实现 PagerSlidingTabStrip.TabCustomViewProvider 并覆盖 getPageTabCustomView

@Override
public View getPageTabCustomView(int position) {
  // return a custom view
}

编辑:为了使用自定义选项卡 View ，您需要使用这个分支: https://github.com/astuetz/PagerSlidingTabStrip/pull/32