相关疑难解决方法(0)

什么是空指针异常(java.lang.NullPointerException)以及它们的原因是什么？

可以使用哪些方法/工具来确定原因,以便停止异常导致程序过早终止？

我正在使用一个ViewPager片段,其中有两个片段作为孩子.这很好用,但是当我用ViewPager另一个片段替换片段并用片段替换这个片段时,ViewPager我的应用程序崩溃了以下内容NullPointerException:

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
    at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:667)
    at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
    at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1319)
    at android.view.View.dispatchRestoreInstanceState(View.java:13756)
    at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2888)
    at android.view.View.restoreHierarchyState(View.java:13734)
    at android.support.v4.app.Fragment.restoreViewState(Fragment.java:468)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1094)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:135)
    at android.app.ActivityThread.main(ActivityThread.java:5294)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

我的ViewPager片段由以下源代码组成,这些源代码在它们为空时实例化两个子片段.此外,ViewPagerAdapter实施是实例化并分配给ViewPager.

public class ConnectionPasswordViewPagerFragment extends Fragment
{
    private ViewPager vpConnectionPassword;
    private …