Android.support.v4.app.FragmentManagerImpl catch NullPointerException？

Question

我需要通过FragmentManagerImpl捕获NullPointerException。
但是尝试...catch不起作用。
如何在getItem（）上捕获显式的NullPointerException？

.......
        try {
              pagerAdapter = new TFragmentPagerAdapter(getFragmentManager());
        } catch (Exception e) {
            Log.e(LOG_TAG, e.toString());
        }

..................

 private class TFragmentPagerAdapter extends FragmentPagerAdapter {

        public TFragmentPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {

            Fragment fragment = null;
            switch (training) {
                case VAR:
//                    fragment = getTFragment(position);
                    fragment = null;
                    break;
                default:
                    break;
            }

            if (fragment == null) {
                throw new RuntimeException();
            }

            return fragment;
        }
}

我看到堆栈跟踪

java.lang.NullPointerException：试图在Android.support.v4.view.viewPager.AddNewItem(ViewPager.java:8)的Android.support.v4.app.backStackRecord.doaddop(BackStackRecord.java:417)的Android.support.v4.app.backStackRecord.add(BackStackRecord.java:412)的Android.support.v4.app.fragmentPagerAdapter.InstantiateItem(FragentPagerAdapter.java:99)的69）在Android.support.v4.view.viewPager.populate(ViewPager.java:1019)在Android.support.v4.view.viewPager.populate(ViewPager.java:951)在Android.support.v4.view.viewPager.populate(ViewPager.java:951)在Android.support.v4.view.viewPager.onMeasure(ViewPager.java:1473)在Android.view.viewPager.measure(ViewPager.java:1473)在ChildWithMargins(ViewGroup.java:5535)在Android.widget.framelayout.onMeasur(framelayout.java:436)在Android.view.view.v4.widget.drawerlayout.measur(view.java:17547)在Android.support.v4.widget.drawerlayout.onMeasur(drawerlayout.java:868)在Android.view.view.view.view.java:17547)在Android.view.view.view.veasure（drawerlayout.measure（.view.measure（view.java:17547)在Android.view.viewgroup.measureChildWithMargins（viewgroup.java:5535)在Android.support.v7.internal.widget.actionBaroverlayLayout.onMeasure（actionBaroverlayLayout.java:444)在Android.view.view.viewgroup.measure（view.java:17547)在Android.view.viewgroup.measure（view.java:45)在35）在Android.widget.linearandroid.widget.linearlayout.java:1436)android.widget.linearlayout.measureVertical(linearlayout.java:722)android.widget.linearlayout.onMeasur(linearlayout.java:613)android.view.viewgroup.measur(view.java:17547)android.view.view.measur(view.java:17547)android.view.view.measury(viewgroup.onMe:17547)在Android.view.viewrootimpl.performMeasure（viewrootimpl.java:2015)在Android.view.viewrootimpl.measurierarchy（viewrootimpl.java:1173)在Android.view.viewrootimpl.performTraversals（viewrootimpl.java:1173)在Android.view.viewrootimpl.performTraversals（viewrootimpl.java:1379)在Android.view.viewrootimpl.doTraversal（choreographer.java:580)at和在Android.view.choreographer.doFrame(chorographer.java:550)在Android.view.choreographer$framedisplayEventReceiver.run(choreographer.java:753)，在Android.os.handler.handleCallback（handler.java:739)在Android.os.handler.dispatchMessage（handler.java:95)，在Android.app.activityThread.loop（looper.java:135)，在Android.app.activityThread.main com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:903)，地址为com.android.internal.os.zygoteinit.main(zygoteinit.java:698)

Answer 1

你发布的代码基本有效。你的问题在别处。编辑您的文章，并向我们展示ActivityThread.java:5257的代码。

为了供您参考，这段代码显示了您在公共片段getItem（int位置）中尝试做的事情...抛出您想要的异常，并且它可以被捕获。

package org.jf;

public class SomeClass {

    public static void main(String[] args) {
        new SomeClass();
    }

    public SomeClass() {
        try {

            AClass x = new AClass();
            x.getItem(1);
        } catch (Exception e) {

            System.out.println("Caught");
        }
    }

    class AClass {
        public Object getItem(int position) {
            int training = 1;
            Object fragment = null;
            switch (training) {
                case 1:
//                    fragment = getTFragment(position);
                    fragment = null;
                    break;
                default:
                    break;
            }

            if (fragment == null) {
                throw new RuntimeException();
            }

            return fragment;
        }
    }
}