我稍微修改了FragmentStatePagerAdapter，以便能够动态地向寻呼机添加页面（like on this blogpost here）。
问题是，我在棒棒糖前设备上的5个安装中大约有4个直接开始NullPointerException。有时安装工作正常，我可以按照我想要的方式重新启动应用程序，而不会获得任何NullPointerException。这是堆栈跟踪：
12-04 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)
我的适配器：
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();
}
}
this.add(BannerFragment.getInstance(0));每次都会崩溃，我甚至无法捕获NullPointerException块中的try { } catch { }。
该行只添加了带标题的第一页，之后的所有页面都是从Web动态加载的。知道如何解决这个问题吗？