Question

我正在处理其中的标签和片段。在其中一个片段上得到了奇怪的运行时错误：

logcat的：

05-13 09:52:46.052    1276-1276/com.myapp.gridview E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.myapp.gridview, PID: 1276
java.lang.NullPointerException
        at com.myapp.gridview.BoardsFragment.onResume(BoardsFragment.java:34)
        at android.support.v4.app.Fragment.performResume(Fragment.java:1543)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:974)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
        at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:478)
        at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
        at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:544)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)

和片段itslef：

import android.content.Context;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class BoardsFragment extends Fragment{
    private GridView gridView;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle    savedInstanceState) {
        View v = inflater.inflate(R.layout.activity_main, container, false);
        gridView = (GridView) v.findViewById(R.id.gridview);
        return v;
    }
    @Override
    public void onResume(){
        super.onResume();
        gridView.setAdapter(new MyAdapter(getActivity()));

    }

    private class MyAdapter extends BaseAdapter
    {
        private List<Item> items = new ArrayList<Item>();
        private LayoutInflater inflater;

        public MyAdapter(Context context)
        {
            inflater = LayoutInflater.from(context);

            items.add(new Item("APO Supreme", R.drawable.snb_apo_supreme));
            items.add(new Item("Arbor Blacklist", R.drawable.snb_arbor_blacklist));
            items.add(new Item("Arbor Draft", R.drawable.snb_arbor_draft));
            items.add(new Item("Arbor Relapse", R.drawable.snb_arbor_relapse));
            items.add(new Item("Capita Defenders of Awesome", R.drawable.snb_capita_defenders_of_awesome));
            items.add(new Item("Capita Outsiders", R.drawable.snb_capita_outsiders));
            items.add(new Item("Capita Ultrafear", R.drawable.snb_capita_ultrafear));
            items.add(new Item("DC Focus", R.drawable.snb_dc_focus));
            items.add(new Item("DC Mega", R.drawable.snb_dc_mega));
            items.add(new Item("DC Tone", R.drawable.snb_dc_tone));
            items.add(new Item("ROME Agent", R.drawable.snb_rome_agent));
            items.add(new Item("ROME Agent Rocker", R.drawable.snb_rome_agent_rocker));
            items.add(new Item("ROME Hammerhead", R.drawable.snb_rome_hammerhead));

    }

    @Override
    public int getCount() {
        return items.size();
    }

    @Override
    public Object getItem(int i)
    {
        return items.get(i);
    }

    @Override
    public long getItemId(int i)
    {
        return items.get(i).picId;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup)
    {
        View v = view;
        ImageView picture;
        TextView name;

        if(v == null)
        {
            v = inflater.inflate(R.layout.gridview_item, viewGroup, false);
            v.setTag(R.id.picture, v.findViewById(R.id.picture));
            v.setTag(R.id.text, v.findViewById(R.id.text));
        }

        picture = (ImageView)v.getTag(R.id.picture);
        name = (TextView)v.getTag(R.id.text);

        Item item = (Item)getItem(i);

        picture.setImageResource(item.picId);
        name.setText(item.name);

        return v;
    }

    private class Item
    {
        final String name;
        final int picId;

        Item(String name, int drawableId)
        {
            this.name = name;
            this.picId = drawableId;
        }
    }
}

}

任何想法onResume()在这里有什么问题？ Perhabs它与support.v4库有关。可能那些库需要一些“特殊”覆盖onResume等？

感谢您的回答

修改

activity_main.xml中：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.myapp.gridview.MainActivity" />

具有GridView的fragment_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<GridView
    android:id="@+id/gridview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:verticalSpacing="0dp"
    android:horizontalSpacing="0dp"
    android:stretchMode="columnWidth"
    android:numColumns="2"
/>
</FrameLayout>

Answer 1

任何想法onResume（）在这里有什么问题？

没错。

Perhabs它与support.v4库有关。

NUllPointerException与支持库无关

可能这些图书馆需要一些特殊的＃34;覆盖onResume等？

库没有特殊的onResume

你有

View v = inflater.inflate(R.layout.activity_main, container, false);

我猜你在Activity中正在夸大Fragment布局。 gridView为空。

应该是

View v = inflater.inflate(R.layout.fragment_main, container, false);

GridView

中可能有fragment_main.xml

Answer 2

只有两种可能性。 gridView或getActivity（）为null。您可以轻松地检测到这一点在这一行上设一个断点。调试您的应用。然后选择gridView并按cmd + shift + I组合以查看gridView的值（对getActivity（）重复这些步骤）。

如果gridView为null，则可以在onResume（）中初始化它。

如果getActivity（）为null，则应覆盖onActivityCreated（）并在其中设置gridView适配器。

onResume（）的java.lang.NullPointerException。有任何想法吗？

2 个答案: