ViewPager FragmentPagerAdapter Nullpointer ViewPager是一种Android支持库中的控件，它允许用户在多个页面之间滑动。FragmentPagerAdapter是ViewPager的一个适配器，用于管理ViewPager中的Fragment。Nullpointer是一个异常，通常会出现在代码中，表示某个对象为空，导致无法执行相应的操作。

我在使用Android的支持库中的ViewPager时遇到了这个错误。这个错误来自于支持包中的横向滑动视图和ViewPager教程。

错误日志如下：

06-19 13:07:25.950: E/AndroidRuntime(16382): FATAL EXCEPTION: main

06-19 13:07:25.950: E/AndroidRuntime(16382): java.lang.NullPointerException

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:347)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:342)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:649)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.view.ViewPager.populate(ViewPager.java:783)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1016)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.View.measure(View.java:12728)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:594)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:376)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.View.measure(View.java:12728)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.View.measure(View.java:12728)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1369)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.LinearLayout.measureVertical(LinearLayout.java:660)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.LinearLayout.onMeasure(LinearLayout.java:553)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.View.measure(View.java:12728)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)

06-19 13:07:25.950: E/AndroidRuntime(16382): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2092)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.View.measure(View.java:12728)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1064)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.os.Handler.dispatchMessage(Handler.java:99)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.os.Looper.loop(Looper.java:137)

06-19 13:07:25.950: E/AndroidRuntime(16382): at android.app.ActivityThread.main(ActivityThread.java:4424)

06-19 13:07:25.950: E/AndroidRuntime(16382): at java.lang.reflect.Method.invokeNative(Native Method)

06-19 13:07:25.950: E/AndroidRuntime(16382): at java.lang.reflect.Method.invoke(Method.java:511)

06-19 13:07:25.950: E/AndroidRuntime(16382): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)

06-19 13:07:25.950: E/AndroidRuntime(16382): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)

06-19 13:07:25.950: E/AndroidRuntime(16382): at dalvik.system.NativeStart.main(Native Method)