Question

getArguments（）在第一次为Frag1调用OnCreateView（）时返回正确的JSON字符串，但是当我滑动到Frag2并且再次调用Frag1的OnCreateView（）时则不返回。相反，“JSON”参数为null。

的活动：

SparkleViewPagerLayout sparkleViewPagerLayout = (SparkleViewPagerLayout) 
findViewById(R.id.view_pager_layout);
FragmentManager fm = getSupportFragmentManager();
sparkleViewPagerLayout.getViewPager().setAdapter(new FragmentPagerAdapter(fm) {
        @Override
        public int getCount() {
            return 4;
        }

        @Override
        public Fragment getItem(int pos) {
            switch (pos) {
                case 0:
                    return Frag0.newInstance(json0);
                case 1:
                    return Frag1.newInstance(json1); // <--THE FAILING FRAGMENT
                case 2:
                    return Frag2.newInstance(json2);
                case 3:
                    return Frag3.newInstance(json3);
                default:
                    return Frag0.newInstance(json0);
            }
        }
    });

片段：

public class Frag1 extends Fragment {
private ArrayList<Thing> things;
private Gson gson = new Gson();

public static Frag1 newInstance(String json) {
    Bundle args = new Bundle();
    args.putString("JSON", json);
    args.putInt("background", R.drawable.img_thing_bg_blurred);
    Frag1 fragment = new Frag1();
    fragment.setArguments(args);

    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.thing_detailed, parent, false);
    int background = getArguments().getInt("background");
    Util.setBackground(v, background, getContext());

    String json = getArguments().getString("JSON");
    things = gson.fromJson(json, new TypeToken<ArrayList<Thing>>() {
    }.getType());

    setUpThingOne(v);

    FragmentManager fm = getChildFragmentManager();
    Fragment listFragment = fm.findFragmentById(R.id.thingFragmentListContainer);
    // We removed the thing in position one, need to update the JSON to reflect this change.
    String jsonNew = gson.toJson(things);
    if (listFragment == null) {
        Bundle bundle = new Bundle();
        bundle.putString("THINGLIST", jsonNew);
        listFragment = new ThingListFragment();
        listFragment.setArguments(bundle);
        fm.beginTransaction()
                .add(R.id.ThingFragmentListContainer, listFragment)
                .commit();
    }

    return v;
}

    private void setUpThingOne(View v) {
        TextView name = (TextView) v.findViewById(R.id.thingName);
        TextView type = (TextView) v.findViewById(R.id.thingField);
        ImageView dollarImg = (ImageView) v.findViewById(R.id.thingPrice);
        ImageView bgImg = (ImageView) v.findViewById(R.id.thingBg);

        for (Thing thing : things) {
            if (thing.getPosition() == 1) {
                name.setText(thing.getName());
                type.setText(thing.getField());
                Util.setDollarImage(getContext(), dollarImg, thingSpot.getPrice());
                RequestUtil.getImage2(getContext(), thing.getImage_url(), bgImg);

                //Remove the #1 thing so that we can make a fragment list from the others.
                //things.remove(thing);
                break;
            }
        }
    }
}

崩溃日志：

01-28 13:43:08.117 31378-31378/com.test.test E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.test.test, PID: 31378
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Iterator java.util.ArrayList.iterator()' on a null object reference
       at com.test.test.fragments.Frag1.setUpThingOne(Frag1.java:78)
       at com.test.test.fragments.Frag1.onCreateView(Frag1.java:48)
       at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
       at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
       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.executePendingTransactions(FragmentManager.java:570)
       at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
       at android.support.v4.view.ViewPager.populate(ViewPager.java:1106)
       at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
       at android.support.v4.view.ViewPager$3.run(ViewPager.java:251)
       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
       at android.view.Choreographer.doCallbacks(Choreographer.java:670)
       at android.view.Choreographer.doFrame(Choreographer.java:603)
       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
       at android.os.Handler.handleCallback(Handler.java:739)
       at android.os.Handler.dispatchMessage(Handler.java:95)
       at android.os.Looper.loop(Looper.java:148)
       at android.app.ActivityThread.main(ActivityThread.java:5417)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

视图寻呼机将您的片段存储在内存中。可能是方法newInstance仅在第一次创建片段时运行。当它在屏幕上不可见时，可以调用其onDestroyView()，然后再次显示它并调用onCreateView()回调（newInstance将永远不会被触发）。这就解释了为什么onCreateView()上的参数为空。您在所有片段回调中调用put log以查看片段的状态。检查Android以获取有关片段生命周期的更多详细信息。

Answer 2

好吧，结果我做了一些复制粘贴时并不是很小心。我认为当我刷到Frag2时onCreateView（）被调用为Frag1并且我意识到我在Frag2中创建了一个新的Frag1而不是Frag2时，我觉得很奇怪......很多小时浪费在本来应该没有发生的事情上！

getArguments（）返回null

2 个答案: