Android 修改的FragmentStatePagerAdapter在棒棒糖前抛出一个NullPointerException
我对FragmentStatePagerAdapter进行了一些修改，以获得向寻呼机动态添加页面的能力（） 问题是，我在pre-lollipop设备上安装了大约5个安装中的4个，一开始就收到了一个Android 修改的FragmentStatePagerAdapter在棒棒糖前抛出一个NullPointerException,android,android-fragments,nullpointerexception,fragmentstatepageradapter,Android,Android Fragments,Nullpointerexception,Fragmentstatepageradapter,我对FragmentStatePagerAdapter进行了一些修改，以获得向寻呼机动态添加页面的能力（） 问题是，我在pre-lollipop设备上安装了大约5个安装中的4个，一开始就收到了一个NullPointerException。有时，安装可以正常工作，我可以随时重新启动应用程序，而不会得到任何NullPointerException。以下是堆栈跟踪： 12-04 13:23:46.084 16637-16637/abc E/AndroidRuntime: FATAL EXCEPTION
NullPointerExceptionNullPointerException12-04 13:23:46.084 16637-16637/abc E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:116)
at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:870)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1020)
at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15518)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1489)
at android.view.View.measure(View.java:15518)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:681)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2176)
at android.view.View.measure(View.java:15518)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1874)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1089)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1265)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
at android.view.Choreographer.doCallbacks(Choreographer.java:562)
at android.view.Choreographer.doFrame(Choreographer.java:532)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5041)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
at dalvik.system.NativeStart.main(Native Method)
private class BannerPagerAdapter extends FragmentStatePagerAdapter {
private ArrayList<WeakReference<Fragment>> registeredFragments = new ArrayList<>();
public BannerPagerAdapter(FragmentManager fm) {
super(fm);
this.add(BannerFragment.getInstance(0)); // <- this is crashing
}
@Override
public Fragment getItem(int position) {
WeakReference<Fragment> weakReference = registeredFragments.get(position);
return weakReference.get();
}
@Override
public int getCount() {
return registeredFragments.size();
}
@Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
public void add(Fragment f){
registeredFragments.add(new WeakReference<>(f));
notifyDataSetChanged();
}
public void remove(int position){
registeredFragments.remove(position);
notifyDataSetChanged();
}
}
私有类BannerPageAdapter扩展了FragmentStatePagerAdapter{
私有ArrayList registeredFragments=新ArrayList（）；
公共横幅管理器适配器（FragmentManager fm）{
超级（fm）；
this.add（BannerFragment.getInstance（0））；//您不应该使用registeredFragment.add（BannerFragment.getInstance（0））；它是一样的。我只是在寻呼机中调用一个函数，它调用registeredFragment.add（BannerFragment.getInstance（0））；，两个方法都有相同的错误。您能显示BannerFragment类吗，因为我们似乎没有从片段本身获取实例，因此NullPointerException.BannerFragment很好，我将使用if（instance！=null）检查所有这些内容…他一直在做所有这些，直到片段被实际添加。我现在通过稍后添加第一个横幅页面进行了修复，效果不错，但目前还不错。似乎在创建适配器后没有直接实例化某些内容。