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Asked:2022-02-26 10:54:01 +0000 UTC2022-02-26 10:54:01 +0000 UTC

ExpandableListView 适配器。在空对象上获取（int）

  • 772

我哪里错了？首先使用适配器等创建了一个测试可扩展列表视图。但是当我尝试连接时，它给出了一个错误。

    Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference
esport.inyourlife.insport.ExpListAdapter.getChildView

这是这里，我正在尝试通过数据模型显示列表

 package esport.inyourlife.insport.Consts;

public class Tournaments {
    public String id;
    public String TournName;
    public String TAdress;
    public String ToDate;
    public String ToTime;
    public String creator;
    public String sport;
    public String format;
    public String pole;
    public String level;
    public String minyear;
    public String maxteams;
    public String info;

    public Tournaments() {
    }

    public Tournaments(String id, String TName, String TAdress, String TDate, String TTime,
                       String creator, String format, String level, String minyear, String maxteams,
                       String info, String pole, String sport) {
        this.id = id;
        this.TournName = TName;
        this.TAdress = TAdress;
        this.ToDate = TDate;
        this.ToTime = TTime;
        this.creator = creator;
        this.format = format;
        this.level = level;
        this.minyear = minyear;
        this.maxteams = maxteams;
        this.info = info;
        this.pole = pole;
        this.sport = sport;
    }
}

这是适配器代码

package esport.inyourlife.insport;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

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

import esport.inyourlife.insport.Consts.Tournaments;

public class ExpListAdapter extends BaseExpandableListAdapter {

    private ArrayList<List<Tournaments>> mGroups;
    private Context mContext;

    public ExpListAdapter (Context context, ArrayList<List<Tournaments>> groups){
        mContext = context;
        mGroups = groups;
    }

    @Override
    public int getGroupCount() {
        return mGroups.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return mGroups.size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return mGroups.get(groupPosition);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return mGroups.get(groupPosition).get(childPosition);
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
                             ViewGroup parent) {

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.group_view, null);
        }

        if (isExpanded){
            //Изменяем что-нибудь, если текущая Group раскрыта
        }
        else{
            //Изменяем что-нибудь, если текущая Group скрыта
        }

        TextView textGroup = (TextView) convertView.findViewById(R.id.textGroup);
        if (groupPosition==0){
            textGroup.setText("Football");
        } else if (groupPosition==1){
            textGroup.setText("Basketball");
        }

        return convertView;

    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
                             View convertView, ViewGroup parent) {
        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.child_view, null);
        }

        TextView textChild = (TextView) convertView.findViewById(R.id.textChild);
        textChild.setText((mGroups.get(groupPosition).get(childPosition)).ToDate);



        return convertView;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

以及我在需要时应用它的代码

 ArrayList<List<Tournaments>> groups = new ArrayList<>();
            ArrayList<String> listDatas = new ArrayList<String>();
            ArrayList<Tournaments> children2 = new ArrayList<>();
            FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
            reference.child("Users").child(user.getUid()).child("Tournaments").addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    if (listDatas.size() > 0) {
                        listDatas.clear();
                    }
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Tournaments getTurn = dataSnapshot.getValue(Tournaments.class);
                        if (getTurn != null) {
                            listTemp.add(getTurn);
                            /*listDatas.add(getTurn.TournName + ", " + getTurn.sport + ", " + getTurn.format +
                                    ", " + getTurn.TAdress + ", " + getTurn.ToDate + "." + getTurn.ToTime +
                                    ", " + getTurn.minyear);*/
                        }                }            }@Override public void onCancelled(@NonNull DatabaseError error) {}
            });
            groups.add(listTemp);

            groups.add(children2);
            //Создаем адаптер и передаем context и список с данными
            ExpListAdapter adapter = new ExpListAdapter(getActivity(), groups);
            turnirs.setAdapter(adapter);

android

1 个回答

  1. Best Answer

    所以我发现了问题。感谢@Style-7 对另一个问题的提示。问题是当我应该输入 listDatas 时，我在 listTemp 中输入了数据。我只是需要一个新的外观或类似的东西。我还将数据类型更改为 ArrayList(ArrayList)。我经常在这里遇到未解决的主题，很难找到解决方案，所以如果您需要在 expendableListView 中显示来自 firebase 的数据，那么这里是解决方案：

    ExpandableListView turnirs = (ExpandableListView)root.findViewById(R.id.expListView);
            //Создаем набор данных для адаптера
            ArrayList<ArrayList<Tournaments>> groups = new ArrayList<ArrayList<Tournaments>>();
            ArrayList<Tournaments> listDatas = new ArrayList<Tournaments>();
            ArrayList<Tournaments> children2 = new ArrayList<>();
            FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
            reference.child("Users").child(user.getUid()).child("Tournaments").addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    if (listDatas.size() > 0) {
                        listDatas.clear();
                    }
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Tournaments getTurn = dataSnapshot.getValue(Tournaments.class);
                        if (getTurn != null) {
                            listDatas.add(getTurn);
                            /*listDatas.add(getTurn.TournName + ", " + getTurn.sport + ", " + getTurn.format +
                                    ", " + getTurn.TAdress + ", " + getTurn.ToDate + "." + getTurn.ToTime +
                                    ", " + getTurn.minyear);*/
                        }                }            }@Override public void onCancelled(@NonNull DatabaseError error) {}
            });
            groups.add(listDatas);

            groups.add(listDatas);
            //Создаем адаптер и передаем context и список с данными
            ExpListAdapter adapter = new ExpListAdapter(getActivity(), groups);
            turnirs.setAdapter(adapter);

    首先，我们调用所有数据，然后，如有必要，将其传递给我们的适配器：

    package esport.inyourlife.insport;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

import com.google.type.DateTime;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.Locale;

import esport.inyourlife.insport.Consts.Tournaments;

import static android.media.CamcorderProfile.get;

public class ExpListAdapter extends BaseExpandableListAdapter {

    private ArrayList<ArrayList<Tournaments>> mGroups;
    private Context mContext;

    public ExpListAdapter (Context context, ArrayList<ArrayList<Tournaments>> groups){
        mContext = context;
        mGroups = groups;
    }

    @Override
    public int getGroupCount() {
        return mGroups.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return mGroups.get(groupPosition).size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return mGroups.get(groupPosition);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return mGroups.get(groupPosition).get(childPosition);
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
                             ViewGroup parent) {

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.group_view, null);
        }

        if (isExpanded){
            //Изменяем что-нибудь, если текущая Group раскрыта
        }
        else{
            //Изменяем что-нибудь, если текущая Group скрыта
        }
        TextView textGroup = (TextView) convertView.findViewById(R.id.textGroup);
        if (groupPosition==0){
            textGroup.setText("Football");
        } else if (groupPosition==1){
            textGroup.setText("Basketball");
        }

        return convertView;

    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
                             View convertView, ViewGroup parent) {
        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.child_view, null);
        }
        Tournaments tournaments = mGroups.get(groupPosition).get(childPosition);
        TextView textChild = (TextView) convertView.findViewById(R.id.textChild);
        textChild.setText(tournaments.ToDate);
        TextView league = convertView.findViewById(R.id.league);
        league.setText(tournaments.format);
        TextView startto = convertView.findViewById(R.id.tostart);
        startto.setText(tournaments.ToDate);



        return convertView;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

    不要忘记更改/添加您的标记，您就完成了）

    • 1

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