java - fragment : Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference

<分区>

我正在尝试插入一个从我的 SQLite 数据库填充的 GridView，但出现错误

“尝试在空对象引用上调用虚方法‘android.view.View android.view.View.findViewById(int)’”

MyAdapter.java 类

public class MyAdapter extends BaseAdapter {
Context context;
ArrayList<Players> playerList;
private static LayoutInflater inflater = null;

public MyAdapter(Context context, ArrayList<Players> playerList){
    this.context = context;
    this.playerList = playerList;
    inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}


@Override
public int getCount() {
    return playerList.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) {
    if (convertView == null)
        convertView = inflater.inflate(R.layout.layout_grid_item, null);

    TextView idTextView = (TextView) convertView.findViewById(R.id.tv_player_id);
    TextView nameTextView = (TextView) convertView.findViewById(R.id.tv_player_name);
    TextView roleTextView = (TextView) convertView.findViewById(R.id.tv_player_role);

    Players p = new Players();
    p = playerList.get(position);
    idTextView.setText("ID " + String.valueOf(p.getId()));
    nameTextView.setText("Name " + String.valueOf(p.getName()));
    roleTextView.setText("Role " + String.valueOf(p.getRole()));

    return convertView;
}

GameActivity.java 类

public class GameActivity extends Activity {
DatabaseHelper db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.game_activity);
    db = new DatabaseHelper(this);

}

public void FragmentOneClick(View view) {
    Fragment myfragment;
    myfragment = new RolesFragment();

    FragmentManager fm = getFragmentManager();
    FragmentTransaction fragmentTransaction = fm.beginTransaction();
    fragmentTransaction.replace(R.id.fragment_switch, myfragment);
    fragmentTransaction.commit();
}

RolesFragment.java

public class RolesFragment extends Fragment {

GridView gridView;
ArrayList<Players> playersList;
MyAdapter adapter;

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

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

    gridView = (GridView) getView().findViewById(R.id.gv_players);

    DatabaseHelper databaseHelper = new DatabaseHelper(getActivity());
    playersList = new ArrayList<Players>();

    playersList = databaseHelper.getPlayers();
    adapter = new MyAdapter(getActivity(), playersList);
    gridView.setAdapter(adapter);

    return view;
}

最佳答案

问题是 getView() 返回 null。

在 fragment 中你必须使用: fragment 的 View 实例。

所以代替:

gridView = (GridView) getView().findViewById(R.id.gv_players);

使用:

 gridView = (GridView) view.findViewById(R.id.gv_players);

关于java - fragment : Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43052407/

上一篇：java - Cucumber Java - 如何在下一步中使用返回的字符串？

下一篇：java - 对象的所有实例是否共享一个 volatile 变量？

相关文章：

java - 为什么我的程序中不能调用这个方法？

java - 如何用 Java 绘制图形

android - 如何在非亚马逊 AppStore Kindle Fire 应用程序中嵌入高分辨率图标？

android - 带有 Picasso 的 Google map 群集项目标记图标

android - 突出显示可点击跨度点击

c# - 让数据库连接保持打开状态？

java - 使用 Stream 从 List 中查找匹配昂贵条件的最后一个元素

java - 添加到单链表时自动按字段对对象进行排序？

java - SQLite查询产生最后一个但一行值而不是最后插入的行值

mysql - MySQL 或 SQLite 是否支持 'INSERT OR UPDATE' 语句？