Question

我有一个片段和活动，里面有gridview。它首先启动片段的活动。并且片段内有按钮将打开或启动gridview活动。我的代码中没有红线，所以我运行该项目。但是当我打开片段上的按钮时，它会返回错误或崩溃。

它说

＆＃34;无法启动活动ComponentInfo（EpicList）：java.lang.NullPointetException：尝试调用虚方法＆＃39; void android.widget.GridView.setAdapter（android.widget.ListAdapter）＆＃39;在null对象引用＆＃34;

这是所有代码

//片段

BundleEpic.java

public class BundleEpic extends Fragment {


    public BundleEpic() {
        // Required empty public constructor
    }

    private ImageView imageView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.activity_bundleepic, container, false);

        imageView = (ImageView) view.findViewById(R.id.imageView);
        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
            Intent intent = new Intent(getActivity(), EpicList.class);
            startActivity(intent);
            }
        });

        return view;
    }
}

//使用Gridview的BasicActivity

EpicList.java

  public class EpicList extends AppCompatActivity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_bundleepic);

            GridView gridView = (GridView)findViewById(R.id.gridview);

            List<EpicListItem> epicListItems = getEpicListItemList();
            EpicListAdapter epicListAdapter = new EpicListAdapter(EpicList.this, epicListItems);
            gridView.setAdapter(epicListAdapter);

            gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                    final Intent intent;
                    switch (position) {
                        case 0:
                            intent = new Intent(EpicList.this, MainActivity.class);
                            break;

                        default:
                            intent = new Intent(EpicList.this, MainActivity.class);
                            break;
                    }
                    EpicList.this.startActivity(intent);
                }
            });
        }


        private List<EpicListItem> getEpicListItemList() {
            EpicListItem epicListItem = null;
            List<EpicListItem> items = new ArrayList<>();
            items.add(new EpicListItem(R.drawable.border_epic));

            return items;
        }
    }

EpicListAdapter

public class EpicListAdapter extends BaseAdapter {

    private LayoutInflater layoutInflater;
    private List<EpicListItem> epicListItems;
    private Context context;

    public EpicListAdapter(Context context, List<EpicListItem> customizeListView) {
        this.context = context;
        layoutInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        epicListItems = customizeListView;
    }

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

    @Override
    public Object getItem(int position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder listViewHoler;
        if (convertView == null) {
            listViewHoler = new ViewHolder();
            convertView = layoutInflater.inflate(R.layout.activity_epic_item, parent, false);
            listViewHoler.imageInListView = (ImageView)convertView.findViewById(R.id.image);
            convertView.setTag(listViewHoler);
        } else {
            listViewHoler = (ViewHolder)convertView.getTag();
        }

        listViewHoler.imageInListView.setImageResource(epicListItems.get(position).getImageResource());

        return convertView;

    }

    static class ViewHolder {
        ImageView imageInListView;
    }

}

EpicListItem.java

public class EpicListItem {

    private int imageResource;

    public EpicListItem(int imageResource) {
        this.imageResource = imageResource;
    }
    public int getImageResource() {
        return imageResource;
    }

    public void setImageResource(int imageResource) {
        this.imageResource = imageResource;
    }
}

activity_epic.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context=".EpicList"
    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:numColumns="3"
        android:padding="5dp" />
</RelativeLayout>

activity_epic_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <RelativeLayout
        android:layout_width="wrap_content"
        android:padding="5dp"
        android:layout_margin="5dp"
        android:layout_centerHorizontal="true"
        android:layout_height="wrap_content">

        <ImageView
            android:adjustViewBounds="true"
            android:id="@+id/image"
            android:layout_centerHorizontal="true"
            android:scaleType="fitXY"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="10dp"
            android:padding="3dp"/>

    </RelativeLayout>
</RelativeLayout>

Answer 1

如错误所示，它无法将适配器设置为null。

这可能是因为您尝试使用findViewById(int id)查找视图，其中布局尚未膨胀。

从片段中启动活动返回错误

1 个答案: