设置PagerSlidingTabStrip NullPointerException时ViewPager

Question

我正试图在我的应用程序中实现PagerSlidingTabStrip。我做了我该做的一切：

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);

但是当我运行这个应用程序时，它会崩溃，这就是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

在这个库中，错误不能很好地处理。如果您查看PagerAdapter的源代码，您将看到一个方法getPageTitle：support/blob/master/v4/java/android/support/v4/view/PagerAdapter.java#L306-Lundefined

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PagerAdapter的实现中覆盖此方法。

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

如果实际上不需要字符串标题，并且希望选项卡使用自定义视图(如图像)，则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视图，您需要使用这个叉：https://github.com/astuetz/PagerSlidingTabStrip/pull/32

Answer 2

Caused by: java.lang.NullPointerException
at com.astuetz.PagerSlidingTabStrip.notifyDataSetChanged(PagerSlidingTabStrip.java:200)

你在PagerSlidingTabStrip上扔了一个PagerSlidingTabStrip。

这表明PagerAdapter.getPageTitle正在返回null。

Answer 3

您应该重写适配器getPageTitle方法，因为它正在返回空。

@Override

公共CharSequence getPageTitle(int位置)

{

返回tabTitlesposition；

}