我正在尝试制作比赛应用。 它将从服务器接收比赛信息，并将该信息显示到android应用程序中。 但我收到此错误。我是android开发的新手。 我正在使用XAMPP和phpmyadmin。
2020-10-17 12:33:57.758 24170-24170/com.example.GameTour E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.GameTour, PID: 24170
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.example.GameTourMySQL.TournamentAdapter.getItemCount(TournamentAdapter.java:53)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4044)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3849)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1103)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.drawerlayout.widget.DrawerLayout.onLayout(DrawerLayout.java:1231)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3470)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2938)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1952)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8171)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
at android.view.Choreographer.doCallbacks(Choreographer.java:796)
at android.view.Choreographer.doFrame(Choreographer.java:731)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
这是我的代码。它显示错误在第53行。我从一些在线文章中寻求帮助。但是我无法解决问题。我做错了什么？
package com.example.GameTourMySQL;
import android.content.Context;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import com.bumptech.glide.Glide;
import java.util.ArrayList;
import java.util.List;
public class TournamentAdapter extends RecyclerView.Adapter<TournamentAdapter.TournamentViewHolder> {
private final Context mCtx;
private final List<Tournaments> tournaments;
public TournamentAdapter(Context mCtx, List<Tournaments> tournaments) {
this.mCtx = mCtx;
this.tournaments = tournaments;
}
@NonNull
@Override
public TournamentViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(mCtx);
View view = inflater.inflate(R.layout.item_layout, null);
return new TournamentViewHolder(view);
}
@Override
public void onBindViewHolder(TournamentViewHolder holder, int position) {
Tournaments tour = tournaments.get(position);
holder.title.setText(tour.getTitle());
holder.time.setText(tour.getTime());
holder.reward.setText(tour.getReward());
holder.perkill.setText(tour.getPerkill());
holder.entryfee.setText(tour.getFees());
holder.type.setText(tour.getType());
holder.map.setText(tour.getMap());
holder.joincount.setText(tour.getJoin());
holder.total.setText(tour.getTotal());
}
@Override
public int getItemCount() {
return tournaments.size();
}
class TournamentViewHolder extends RecyclerView.ViewHolder {
TextView title, time, reward, perkill, entryfee, type, map, joincount, total;
Button roomPassButton, join;
public TournamentViewHolder(View itemView) {
super(itemView);
title = itemView.findViewById(R.id.title);
time = itemView.findViewById(R.id.time);
reward = itemView.findViewById(R.id.reward);
perkill = itemView.findViewById(R.id.perkill);
entryfee = itemView.findViewById(R.id.entryfee);
type = itemView.findViewById(R.id.type);
map = itemView.findViewById(R.id.map);
joincount = itemView.findViewById(R.id.joincount);
total = itemView.findViewById(R.id.total);
roomPassButton = itemView.findViewById(R.id.roomPassButton);
join = itemView.findViewById(R.id.join);
}
}
}
我该怎么办？ 谢谢
答案 0 :(得分：0)
此错误导致“ NullPointerException”。首先看“什么是NullPointerExcetion？”。手段。
如果您没有给参数赋值，并且使用了函数或参数，则操作系统会为您提供“ NullPointerException”。
在这种情况下。您没有为“比赛”参数分配值。您在下面使用了“大小”功能。
您的问题是“在从数据库向Android应用程序检索数据时出现问题”，但是没有关于数据库或网络信息的说明。 如果出现“ NullPointerException”崩溃，请以“我正在获取Nullpointer异常等”的方式打开问题。 并且请注意，这个问题以前没有被问过。
答案 1 :(得分：0)
首先，在调用适配器的构造函数的地方发布代码，即TournamentAdapter()。从堆栈跟踪中可以明显看出tournaments.size();正在抛出NullPointerException。因此，请检查要发送给适配器的第二个参数是什么。我认为该值为null，因此您得到了例外，希望这能回答您的问题！