android.support.v4.app.FragmentManagerImpl捕获NullPointerException吗? [英] android.support.v4.app.FragmentManagerImpl catch NullPointerException?

问题描述

我需要通过FragmentManagerImpl捕获NullPointerException.
但是请尝试...捕获不起作用.
如何在getItem()上捕获显式的NullPointerException?

I need catch NullPointerException by FragmentManagerImpl.
But try ... catch does not work.
How to catch explicit NullPointerException on getItem()?

.......
        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;
        }
}

我看到的堆栈跟踪

java.lang.NullPointerException:尝试写入字段'android.support.v4.app.FragmentManagerImpl空对象上的android.support.v4.app.Fragment.mFragmentManager'参考在android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:417)在android.support.v4.app.BackStackRecord.add(BackStackRecord.java:412)在android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)在android.support.v4.view.ViewPager.addNewItem(ViewPager.java:869)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.onMeasure(ViewPager.java:1473)在android.view.View.measure(View.java:17547)在android.widget.RelativeLayout.measureChildHorizo​​ntal(RelativeLayout.java:727)在android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)在android.view.View.measure(View.java:17547)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)在android.widget.FrameLayout.onMeasure(FrameLayout.java:436)在android.view.View.measure(View.java:17547)在android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:868)在android.view.View.measure(View.java:17547)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)在android.widget.FrameLayout.onMeasure(FrameLayout.java:436)在android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)在android.view.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.measure(View.java:17547)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)在android.widget.FrameLayout.onMeasure(FrameLayout.java:436)在android.view.View.measure(View.java:17547)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)在android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)在android.widget.LinearLayout.measureVertical(LinearLayout.java:722)在android.widget.LinearLayout.onMeasure(LinearLayout.java:613)在android.view.View.measure(View.java:17547)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)在android.widget.FrameLayout.onMeasure(FrameLayout.java:436)在com.android.internal.policy.impl.PhoneWindow $ DecorView.onMeasure(PhoneWindow.java:2615)在android.view.View.measure(View.java:17547)在android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)在android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)在android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)在android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)在android.view.ViewRootImpl $ TraversalRunnable.run(ViewRootImpl.java:5885)在android.view.Choreographer $ CallbackRecord.run(Choreographer.java:767)在android.view.Choreographer.doCallbacks(Choreographer.java:580)在android.view.Choreographer.doFrame(Choreographer.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.os.Looper.loop(Looper.java:135)在android.app.ActivityThread.main(ActivityThread.java:5257)在java.lang.reflect.Method.invoke(本机方法)在java.lang.reflect.Method.invoke(Method.java:372)在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:903)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:417) at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:412) at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99) at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:869) at android.support.v4.view.ViewPager.populate(ViewPager.java:1019) at android.support.v4.view.ViewPager.populate(ViewPager.java:951) at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1473) at android.view.View.measure(View.java:17547) at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727) at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) at android.view.View.measure(View.java:17547) at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:868) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) at android.view.View.measure(View.java:17547) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535) at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615) at android.view.View.measure(View.java:17547) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) at android.view.Choreographer.doCallbacks(Choreographer.java:580) at android.view.Choreographer.doFrame(Choreographer.java:550) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) 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:5257) 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:903) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

推荐答案

您发布的代码基本上可以正常工作.您的问题出在其他地方.编辑您的文章，并向我们展示有关ActivityThread.java:5257的代码.

The code you posted basically works. Your problem lies elsewhere. Edit your post and show us the code around ActivityThread.java:5257.

此代码供您参考，以显示您正在尝试在公共Fragment getItem(int position)中执行的操作...引发所需的异常，并且可以捕获该异常.

For your reference this code shows what you were trying to do in public Fragment getItem(int position)... throw the exception you want and that it can be caught.

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;
        }
    }
}

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