在我的项目中，我从服务器获取数据并将其显示在Recyclerview中。将数据添加到列表并在getItemCount（）中调用它后，我得到null并抛出异常。
public class AppointmentResponse {
private static final String TAG = "Appointment Response";
@SerializedName("data")
@Expose
private List<AppntRespData> data = null;
@SerializedName("error_code")
@Expose
private String errorCode;
@SerializedName("message")
@Expose
private String message;
@SerializedName("status")
@Expose
private String status;
public List<AppntRespData> getData() {
return data;
}
public AppointmentResponse() {
}
public AppointmentResponse(List<AppntRespData> data, String errorCode, String message, String status) {
this.data = data;
this.errorCode = errorCode;
this.message = message;
this.status = status;
}
public void setData(List<AppntRespData> data) {
this.data = data;
}
public String getErrorCode() {
return errorCode;
}
public void setErrorCode(String errorCode) {
this.errorCode = errorCode;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
@Override
public String toString() {
return "AppointmentResponse{" +
"data=" + data +
", errorCode='" + errorCode + '\'' +
", message='" + message + '\'' +
", status='" + status + '\'' +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
AppointmentResponse that = (AppointmentResponse) o;
if (data != null ? !data.equals(that.data) : that.data != null) return false;
if (errorCode != null ? !errorCode.equals(that.errorCode) : that.errorCode != null)
return false;
if (message != null ? !message.equals(that.message) : that.message != null) return false;
return status != null ? status.equals(that.status) : that.status == null;
}
@Override
public int hashCode() {
int result = data != null ? data.hashCode() : 0;
result = 31 * result + (errorCode != null ? errorCode.hashCode() : 0);
result = 31 * result + (message != null ? message.hashCode() : 0);
result = 31 * result + (status != null ? status.hashCode() : 0);
return result;
}
public static class AppntRespData
{
@SerializedName("with_whom")
@Expose
private String withWhom;
@SerializedName("service_type")
@Expose
private String serviceType;
@SerializedName("appointment_time")
@Expose
private String appointmentTime;
@SerializedName("appointment_status")
@Expose
private String appointmentStatus;
@SerializedName("appointment_id")
@Expose
private String appointmentId;
@SerializedName("appointment_date")
@Expose
private String appointmentDate;
public AppntRespData() {
}
public AppntRespData(String withWhom, String serviceType, String appointmentTime, String appointmentStatus, String appointmentId, String appointmentDate) {
this.withWhom = withWhom;
this.serviceType = serviceType;
this.appointmentTime = appointmentTime;
this.appointmentStatus = appointmentStatus;
this.appointmentId = appointmentId;
this.appointmentDate = appointmentDate;
}
public String getWithWhom() {
return withWhom;
}
public void setWithWhom(String withWhom) {
this.withWhom = withWhom;
}
public String getServiceType() {
return serviceType;
}
public void setServiceType(String serviceType) {
this.serviceType = serviceType;
}
public String getAppointmentTime() {
return appointmentTime;
}
public void setAppointmentTime(String appointmentTime) {
this.appointmentTime = appointmentTime;
}
public String getAppointmentStatus() {
return appointmentStatus;
}
public void setAppointmentStatus(String appointmentStatus) {
this.appointmentStatus = appointmentStatus;
}
public String getAppointmentId() {
return appointmentId;
}
public void setAppointmentId(String appointmentId) {
this.appointmentId = appointmentId;
}
public String getAppointmentDate() {
return appointmentDate;
}
public void setAppointmentDate(String appointmentDate) {
this.appointmentDate = appointmentDate;
}
@Override
public String toString() {
return "AppntRespData{" +
"withWhom='" + withWhom + '\'' +
", serviceType='" + serviceType + '\'' +
", appointmentTime='" + appointmentTime + '\'' +
", appointmentStatus='" + appointmentStatus + '\'' +
", appointmentId='" + appointmentId + '\'' +
", appointmentDate='" + appointmentDate + '\'' +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
AppntRespData that = (AppntRespData) o;
if (withWhom != null ? !withWhom.equals(that.withWhom) : that.withWhom != null)
return false;
if (serviceType != null ? !serviceType.equals(that.serviceType) : that.serviceType != null)
return false;
if (appointmentTime != null ? !appointmentTime.equals(that.appointmentTime) : that.appointmentTime != null)
return false;
if (appointmentStatus != null ? !appointmentStatus.equals(that.appointmentStatus) : that.appointmentStatus != null)
return false;
if (appointmentId != null ? !appointmentId.equals(that.appointmentId) : that.appointmentId != null)
return false;
return appointmentDate != null ? appointmentDate.equals(that.appointmentDate) : that.appointmentDate == null;
}
@Override
public int hashCode() {
int result = withWhom != null ? withWhom.hashCode() : 0;
result = 31 * result + (serviceType != null ? serviceType.hashCode() : 0);
result = 31 * result + (appointmentTime != null ? appointmentTime.hashCode() : 0);
result = 31 * result + (appointmentStatus != null ? appointmentStatus.hashCode() : 0);
result = 31 * result + (appointmentId != null ? appointmentId.hashCode() : 0);
result = 31 * result + (appointmentDate != null ? appointmentDate.hashCode() : 0);
return result;
}
}
}
我的JSON数据提取方法
ApiInterface service = RestClient.getApiInterface();
final Call<AppointmentResponse> AppResp = service.postAppointListData(appntRequest);
AppResp.enqueue(new Callback<AppointmentResponse>() {
@Override
public void onResponse(@NonNull Call<AppointmentResponse> call, @NonNull Response<AppointmentResponse> response) {
try {
if (response.body().getErrorCode().equals("0")) {
AppointmentResponse.AppntRespData mAppData = new AppointmentResponse.AppntRespData();
for (int i=0;i<response.body().getData().size();i++) {
mAppData.setWithWhom(response.body().getData().get(i).getWithWhom());
mAppData.setAppointmentDate(response.body().getData().get(i).getAppointmentDate());
mAppData.setAppointmentId(response.body().getData().get(i).getAppointmentId());
mAppData.setAppointmentStatus(response.body().getData().get(i).getAppointmentStatus());
mAppData.setAppointmentTime(response.body().getData().get(i).getAppointmentTime());
mAppData.setServiceType(response.body().getData().get(i).getServiceType());
//public ArrayList<AppointmentResponse.AppntRespData> appointmentlist;
appointmentlist.add(mAppData);
}
Log.d(TAG, "onResponse: appointList--"+appointmentlist);
}
else {
Toast.makeText(getContext(), response.body().getMessage(), Toast.LENGTH_SHORT).show();;
}
}catch (Exception e)
{
e.getMessage();
}
}
@Override
public void onFailure(@NonNull Call<AppointmentResponse> call, @NonNull Throwable t) {
t.getMessage();
}
});
我的Recycler Adapter类
public class AppointRecycleAdapter extends RecyclerView.Adapter<AppointRecycleAdapter.AppointViewHolder> {
private Context mContext;
private ArrayList<AppointmentResponse.AppntRespData> appointmentlist;
private static final String TAG = "AppointRecycleAdapter";
public AppointRecycleAdapter(Context mContext, ArrayList<AppointmentResponse.AppntRespData> appointmentlist) {
this.mContext = mContext;
this.appointmentlist = appointmentlist;
}
public class AppointViewHolder extends RecyclerView.ViewHolder {
private CardView mCradview;
private TextView tvInsWith,tvInsApDate,tvInsApStatus;
public AppointViewHolder(View itemView) {
super(itemView);
mCradview = itemView.findViewById(R.id.cardViewAppnt);
tvInsApDate = itemView.findViewById(R.id.InsAppntDate);
tvInsApStatus = itemView.findViewById(R.id.InsAppntStatus);
tvInsWith = itemView.findViewById(R.id.Inswith);
}
}
@Override
public AppointViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View mView = LayoutInflater.from(parent.getContext()).inflate(R.layout.appointmentcardlayout,parent,false);
return new AppointViewHolder(mView);
}
@Override
public void onBindViewHolder(AppointViewHolder holder, int position) {
Log.d(TAG, "onBindViewHolder: in");
//final AppointmentResponse.AppntRespData bean = appointmentlist.get(position);
holder.tvInsApStatus.setText(appointmentlist.get(position).getAppointmentStatus());
//holder.tvInsWith.setText(appointmentResponseList.get(position).getWithWhom());
//holder.tvInsApDate.setText(bean.getAppointmentDate());
// holder.tvInsApStatus.setText(appointmentResponseList.get(position).getAppointmentStatus());
Log.d(TAG, "onBindViewHolder: appRespList---------"+appointmentlist);
holder.mCradview.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
AppCompatActivity activity = (AppCompatActivity) view.getContext();
DetailAppointList detailAppointList = new DetailAppointList();
activity.getSupportFragmentManager().beginTransaction()
.replace(R.id.content, detailAppointList).addToBackStack(null).commit();
}
});
}
@Override
public int getItemCount() {
Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size());
//**Here I'm getting Null Pointer exception**
return appointmentlist == null ? 0 : appointmentlist.size();
}
}
答案 0 :(得分：1)
在代码中更改函数getItemCount()
@Override
public int getItemCount() {
//your problem is here because you are printing size of list which is null,
//so instead of that check the null first, then use the list object
if (appointmentlist == null)
Log.d(TAG, "null list");
else
Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size());
//**Here I'm getting Null Pointer exception**
return appointmentlist == null ? 0 : appointmentlist.size();
}
}
答案 1 :(得分：0)
你没有处理此案
当约会列表为空并且您正在呼叫Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size());时，appointmentlist.size()行。这就是它给出NullPointerException
答案 2 :(得分：0)
我在获取JSON方法（实例变量）中将 ArrayList，约会列表声明为静态后得到了答案
public static ArrayList<AppointmentResponse.AppntRespData> appointmentlist;
并在OnResponse（）
中初始化它 i.e before for(int i=0;i<response.body().getData().size();i++)
public void onResponse(@NonNull Call<AppointmentResponse> call, @NonNull Response<AppointmentResponse> response) {
try {
if (response.isSuccessful()) {
appointmentlist = new ArrayList<AppointmentResponse.AppntRespData>();
for (int i=0;i<response.body().getData().size();i++) {
AppointmentResponse.AppntRespData mAppData = new AppointmentResponse.AppntRespData();