java.lang.NullPointerException：尝试在从服务器到微调器的空对象引用上调用接口方法“int java.util.List.size()”

Question

我正在尝试从服务器获取数据到可搜索微调器，但显示为空。我正在使用 改造和检查邮递员上的 api 它显示数据，但在 android studio 中显示 null。我只显示来自 mysql 数据库的国家名称，抱歉英语不好 感谢提前解决我的问题。

public class LabourRegActivity extends AppCompatActivity {

    private ArrayList<String> countryname = new ArrayList<String>();
    SearchableSpinner countryS,catagoryS,cityS,projectbaseS,district;
    EditText name,contact,cnic,perdayrate,address;
    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_labour_reg);



        countryS = findViewById(R.id.country_spinner);
        catagoryS = findViewById(R.id.skill_spinner);
        cityS = findViewById(R.id.city_spinner);
        projectbaseS = findViewById(R.id.projectBase);
        district = findViewById(R.id.district_Spinner);

        name = findViewById(R.id.Edt_name);
        contact = findViewById(R.id.Edt_contact);
        cnic = findViewById(R.id.Edt_cnic);
        perdayrate = findViewById(R.id.Edt_perdays);
        address = findViewById(R.id.Edt_address);



        CountryFetchApi fetchApi = ApiClient.getClient().create(CountryFetchApi.class);
//        HashMap<String, String> map = new HashMap<>();
        Log.d("ok","countryMap"+fetchApi);
        Call<List<CountryModel>> model = fetchApi.getcountryrecord();
        model.enqueue(new Callback<List<CountryModel>>() {
            @Override
            public void onResponse(Call<List<CountryModel>> call, Response<List<CountryModel>> response) {
                List<CountryModel> data = response.body();
                Log.d("ok","country"+response.body());
                for (int i = 0; i < data.size(); i++) {
                    countryname.add(data.get(i).getCountryName());
                }
                Log.d("leavename", countryS.toString());


                adapter = new ArrayAdapter<String>(LabourRegActivity.this, R.layout.support_simple_spinner_dropdown_item,countryname);
                adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                countryS.setAdapter(adapter);

            }

            @Override
            public void onFailure(Call<List<CountryModel>> call, Throwable t) {

            }
        });
    }
}

Answer 1

public class CountryModel {


    @SerializedName("id")
    @Expose
    private Integer id;
    @SerializedName("name")
    @Expose
    private String name;
    @SerializedName("skill")
    @Expose
    private String skill;
    @SerializedName("cnic")
    @Expose
    private Object cnic;
    @SerializedName("contact_number")
    @Expose
    private String contactNumber;
    @SerializedName("labour_amount")
    @Expose
    private String labourAmount;
    @SerializedName("perday_project")
    @Expose
    private Integer perdayProject;
    @SerializedName("company_amount")
    @Expose
    private String companyAmount;
    @SerializedName("address")
    @Expose
    private String address;
    @SerializedName("category_name")
    @Expose
    private String categoryName;
    @SerializedName("city_name")
    @Expose
    private String cityName;
    @SerializedName("province")
    @Expose
    private String province;
    @SerializedName("country_name")
    @Expose
    private String countryName;
    @SerializedName("district_name")
    @Expose
    private String districtName;


    public CountryModel() {
        this.id = id;
        this.name = name;
        this.skill = skill;
        this.cnic = cnic;
        this.contactNumber = contactNumber;
        this.labourAmount = labourAmount;
        this.perdayProject = perdayProject;
        this.companyAmount = companyAmount;
        this.address = address;
        this.categoryName = categoryName;
        this.cityName = cityName;
        this.province = province;
        this.countryName = countryName;
        this.districtName = districtName;
    }

    @Override
    public String toString() {
        return getCountryName();
    }


    public String getId() {
        return String.valueOf(id);
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSkill() {
        return skill;
    }

    public void setSkill(String skill) {
        this.skill = skill;
    }

    public Object getCnic() {
        return cnic;
    }

    public void setCnic(Object cnic) {
        this.cnic = cnic;
    }

    public String getContactNumber() {
        return contactNumber;
    }

    public void setContactNumber(String contactNumber) {
        this.contactNumber = contactNumber;
    }

    public String getLabourAmount() {
        return labourAmount;
    }

    public void setLabourAmount(String labourAmount) {
        this.labourAmount = labourAmount;
    }

    public Integer getPerdayProject() {
        return perdayProject;
    }

    public void setPerdayProject(Integer perdayProject) {
        this.perdayProject = perdayProject;
    }

    public String getCompanyAmount() {
        return companyAmount;
    }

    public void setCompanyAmount(String companyAmount) {
        this.companyAmount = companyAmount;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getCategoryName() {
        return categoryName;
    }

    public void setCategoryName(String categoryName) {
        this.categoryName = categoryName;
    }

    public String getCityName() {
        return cityName;
    }

    public void setCityName(String cityName) {
        this.cityName = cityName;
    }

    public String getProvince() {
        return province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public String getCountryName() {
        return countryName;
    }

    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }

    public String getDistrictName() {
        return districtName;
    }

    public void setDistrictName(String districtName) {
        this.districtName = districtName;
    }

}