我正在尝试在同一个回收视图上进行2次不同的调用，其想法是从2次不同的请求中获取数据，并以足球比赛的ID显示经过验证的球队的盾牌。我知道错误的含义，但是，我真的不知道如何解决。 JSON文件有效，这是错误的。
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.cristhian.consumingapi, PID: 16520
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.isEmpty()' on a null object reference
at com.example.cristhian.consumingapi.ListaPartidosAdapter.setupAdapter(ListaPartidosAdapter.java:99)
at com.example.cristhian.consumingapi.ListaPartidosAdapter.adicionarListaPartidos(ListaPartidosAdapter.java:89)
at com.example.cristhian.consumingapi.MainActivity$1.onResponse(MainActivity.java:76)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Application terminated.
ListaPartidosAdapter
public class ListaPartidosAdapter extends RecyclerView.Adapter<ListaPartidosAdapter.ViewHolder> {
private static final String TAG = "Football_Adapter";
private ArrayList<Partido> dataset;
private ArrayList<Stand> dataset_Stand;
private Context context;
public ListaPartidosAdapter(Context context) {
this.context = context;
dataset = new ArrayList<Partido>();
dataset_Stand = new ArrayList<Stand>();
}
@Override
public ListaPartidosAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_partidos, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(ListaPartidosAdapter.ViewHolder holder, int position) {
Partido p = dataset.get(position);
String status = p.getStatus();
if (status.equals("SCHEDULED")){
String status_ = "SCH";
holder.status.setText(status_);
}
holder.utcDate.setText(p.getUtcDate());
Partido.EquipoCasa homeTeam = p.getHomeTeam();
String id_homeTeam = homeTeam.getId();
holder.homeTeam.setText(homeTeam.getName());
Partido.EquipoVisita awayTeam = p.getAwayTeam();
holder.awayTeam.setText(awayTeam.getName());
Stand s = dataset_Stand.get(position);
Stand.Table table = (Stand.Table) s.getTable();
Stand.Table.Equipo team = (Stand.Table.Equipo) table.getEquipo();
String id_equipo = team.getId();
holder.homeTeam.setText(team.getName());
if(id_homeTeam.equals(id_equipo)){
Glide.with(context)
.load(team.getCrestUrl())
.centerCrop()
.crossFade()
.diskCacheStrategy(DiskCacheStrategy.ALL)
.into(holder.team);
}
}
@Override
public int getItemCount() {
return 0;
}
public void adicionarListaPartidos(ArrayList<Partido> listaPartidos){
setupAdapter(listaPartidos, null);
}
public void adicionarListaStands(ArrayList<Stand> listaStands){
setupAdapter(null, listaStands);
}
private void setupAdapter(ArrayList<Partido> listaPartidos, ArrayList<Stand> listaStands) {
if(!listaPartidos.isEmpty() && !listaStands.isEmpty()){
addItemsToAdapter(listaPartidos,listaStands);
}
}
public void addItemsToAdapter(ArrayList<Partido> listaPartidos, ArrayList<Stand> listaStands){
notifyDataSetChanged();
}
public class ViewHolder extends RecyclerView.ViewHolder {
private TextView status;
private TextView utcDate;
private TextView homeTeam;
private TextView awayTeam;
public ImageView team;
public ViewHolder(View itemView) {
super(itemView);
status = (TextView) itemView.findViewById(R.id.status);
utcDate = (TextView) itemView.findViewById(R.id.utcDate);
homeTeam = (TextView) itemView.findViewById(R.id.homeTeam);
awayTeam = (TextView) itemView.findViewById(R.id.awayTeam);
team = (ImageView) itemView.findViewById(R.id.team);
}
}
}
这是我的MainActivity.java。
public class MainActivity extends AppCompatActivity {
private Retrofit retrofit;
private static final String TAG = "Football";
private RecyclerView recyclerView;
private ListaPartidosAdapter listaPartidosAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView)findViewById(R.id.recyclerView);
listaPartidosAdapter = new ListaPartidosAdapter(this);
recyclerView.setAdapter(listaPartidosAdapter);
recyclerView.setHasFixedSize(true);
final LinearLayoutManager layoutManager = new LinearLayoutManager(this, VERTICAL, true);
recyclerView.setLayoutManager(layoutManager);
retrofit = new Retrofit.Builder()
.baseUrl("http://api.football-data.org/v2/")
.addConverterFactory(GsonConverterFactory.create())
.build();
obtenerDatos();
}
private void obtenerDatos() {
Calendar calendar = Calendar.getInstance();
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
String todayDate=df.format(calendar.getTime());
calendar.add(Calendar.DATE,3);
String endDate = df.format(calendar.getTime());
Log.i(TAG, "todayDate : " + todayDate);
Log.i(TAG, "endDate : " + endDate);
footballdataService service = retrofit.create(footballdataService.class);
Call<PartidosRespuesta> partidosRespuestaCall = service.obtenerlistaPartidos(todayDate,endDate);
Call<StandingsRespuesta> standingsRespuestaCall = service.obtenerStandings();
partidosRespuestaCall.enqueue(new Callback<PartidosRespuesta>() {
@Override
public void onResponse(Call<PartidosRespuesta> call, Response<PartidosRespuesta> response) {
if(response.isSuccessful()) {
PartidosRespuesta partidosRespuesta = response.body();
List<Partido> listaPartidos = partidosRespuesta.getMatches();
listaPartidosAdapter.adicionarListaPartidos((ArrayList<Partido>) listaPartidos);
}
else {
Log.e(TAG, "onResponse: " + response.errorBody());
}
}
@Override
public void onFailure(Call<PartidosRespuesta> call, Throwable t) {
Log.e(TAG, "onFailure: " + t.getMessage());
}
});
standingsRespuestaCall.enqueue(new Callback<StandingsRespuesta>() {
@Override
public void onResponse(Call<StandingsRespuesta> call, Response<StandingsRespuesta> response) {
if(response.isSuccessful()) {
StandingsRespuesta standingsRespuesta = response.body();
List<Stand> listaStands = standingsRespuesta.getStandings();
listaPartidosAdapter.adicionarListaStands((ArrayList<Stand>) listaStands);
}
}
@Override
public void onFailure(Call<StandingsRespuesta> call, Throwable t) {
}
});
}
}
答案 0 :(得分：1)
根据经验，将“无元素”表示为空列表是很糟糕的。从一开始就最好确保在这种情况下，您传递一个 empty 列表。就您而言，在此行之后
List<Stand> listaStands = standingsRespuesta.getStandings();
插入以下内容
if (listaStands == null) {
listaStands = Collections.emptyList();
}
（未经测试）
答案 1 :(得分：0)
您正在使用空值作为参数调用setupAdapter（）函数，但尚未进行空检查。
private void setupAdapter(@Nullable ArrayList<Partido> listaPartidos, @Nullable ArrayList<Stand> listaStands) {
if((listaPartidos != null && !listaPartidos.isEmpty()) //this might throw NPE
|| (listaStands != null && !listaStands.isEmpty()) //This might throw NPE ){
addItemsToAdapter(listaPartidos,listaStands);
}
}
您应根据您的应用逻辑添加空检查。