为什么我的名字和姓氏都为空？

Question

嗨，我是 API 的初学者，我正在尝试使用改造从 https://reqres.in/api/users?page=2 获取数据我能够成功获取电子邮件和图片，但是名字和姓氏显示为空，为什么？

look at the pic to understand what i am talking about

ActivityForUserBinding binding;
recycle recycle_adapter;
api_interface api;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    binding = ActivityForUserBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());

    api = Retrofit_instance.get_retrofit_for_users().create(api_interface.class);

    api.get_users(2).enqueue(new Callback<pojo_for_users>() {
        @Override
        public void onResponse(Call<pojo_for_users> call, Response<pojo_for_users> response) {
            if(response.isSuccessful()){

                recycle_adapter = new recycle(response.body().getData());
                binding.recycleView.setAdapter(recycle_adapter);

            }
        }

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

        }
    });

}

public class recycle extends RecyclerView.Adapter<recycle.MyViewHolder>{

    List<pojo_for_users.Datum> list;

    public recycle(List<pojo_for_users.Datum> list) {
        this.list = list;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.get_user_profile_holder,parent,false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        holder.firstName.setText(String.valueOf(list.get(position).getFirstName()));
        holder.email.setText(String.valueOf(list.get(position).getEmail()));
        holder.lastName.setText(String.valueOf(list.get(position).getLastName()));
        Glide.with(getApplicationContext()).load(list.get(position).getAvatar()).centerCrop().placeholder(R.drawable.ic_launcher_background).into(holder.userProfile);
    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {

        private ImageView userProfile;
        private ConstraintLayout constraintLayout;
        private TextView justText;
        private TextView justTextt;
        private TextView email;
        private TextView lastName;
        private TextView firstName;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);

            userProfile = (ImageView) itemView.findViewById(R.id.user_profile);
            constraintLayout = (ConstraintLayout) itemView.findViewById(R.id.constraintLayout);
            justText = (TextView) itemView.findViewById(R.id.just_text);
            justTextt = (TextView) itemView.findViewById(R.id.just_textt);
            email = (TextView) itemView.findViewById(R.id.email);
            lastName = (TextView) itemView.findViewById(R.id.last_name);
            firstName = (TextView) itemView.findViewById(R.id.first_name);

        }
    }
}

}

这就是我的 pojo 课

public class pojo_for_users {


private Integer page;

private Integer perPage;

private Integer total;

private Integer totalPages;

private List<Datum> data = null;

private Support support;

private Map<String, Object> additionalProperties = new HashMap<String, Object>();


public Integer getPage() {
    return page;
}


public void setPage(Integer page) {
    this.page = page;
}


public Integer getPerPage() {
    return perPage;
}


public void setPerPage(Integer perPage) {
    this.perPage = perPage;
}


public Integer getTotal() {
    return total;
}


public void setTotal(Integer total) {
    this.total = total;
}


public Integer getTotalPages() {
    return totalPages;
}


public void setTotalPages(Integer totalPages) {
    this.totalPages = totalPages;
}


public List<Datum> getData() {
    return data;
}


public void setData(List<Datum> data) {
    this.data = data;
}


public Support getSupport() {
    return support;
}


public void setSupport(Support support) {
    this.support = support;
}


public Map<String, Object> getAdditionalProperties() {
    return this.additionalProperties;
}


public void setAdditionalProperty(String name, Object value) {
    this.additionalProperties.put(name, value);
}

public class Datum {


    private Integer id;

    private String email;

    private String firstName;

    private String lastName;

    private String avatar;

    private Map<String, Object> additionalProperties = new HashMap<String, Object>();


    public Integer getId() {
        return id;
    }


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


    public String getEmail() {
        return email;
    }


    public void setEmail(String email) {
        this.email = email;
    }


    public String getFirstName() {
        return firstName;
    }


    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }


    public String getLastName() {
        return lastName;
    }


    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getAvatar() {
        return avatar;
    }


    public void setAvatar(String avatar) {
        this.avatar = avatar;
    }


    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }


    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

}

public class Support {


    private String url;

    private String text;

    private Map<String, Object> additionalProperties = new HashMap<String, Object>();


    public String getUrl() {
        return url;
    }


    public void setUrl(String url) {
        this.url = url;
    }


    public String getText() {
        return text;
    }


    public void setText(String text) {
        this.text = text;
    }


    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }


    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

}

}

创建改造实例

public class Retrofit_instance {


private static Retrofit retrofit;
private static Retrofit retrofit1;
private final static String Base_url = "http://universities.hipolabs.com/";
private final static String Base_url_fo_users = "https://reqres.in/api/";

public static Retrofit get_retrofit(){

    if (retrofit == null){
        retrofit = new retrofit2.Retrofit.Builder()
                .baseUrl(Base_url)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }

    return retrofit;
}

public static Retrofit get_retrofit_for_users(){

    if (retrofit1 == null){
        retrofit1 = new retrofit2.Retrofit.Builder()
                .baseUrl(Base_url_fo_users)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }

    return retrofit1;
}

}

这是我的api接口

public interface api_interface {

@GET("search?")
Call<List<pojo>>getdata(@Query("country") String Country);

@GET("users")
Call<pojo_for_users>get_users(

        @Query("page") int page_number

);

}

提前致谢。

Answer 1

Retrofit 使用Gson 将原始JSON 转换为Java 对象。转换时，Gson 在您的 Java 类中查找 API 返回的字段名称。

基本上，您必须告诉Gson 映射值的位置。您可以通过两种方式实现这一目标，

1. 使用准确的 JSON 字段名称命名变量。

   @Expose
   private String first_name;
   
   @Expose
   private String last_name;
   

   请注意，您需要添加@Expose 注释以避免在混淆过程中更改变量名称（当您的build.gradle 中有minifiyEnabled true 时）。

2. 给变量添加@SerializedName注解。

   @SerializedName("first_name")
   private String firstName;
   
   @SerializedName("last_name")
   private String lastName;
   

Answer 2

根据您的 JSON 响应，firstName 和 lastName 带有下划线，如下所示。像下面这样更改编码后一切都会好起来的。

private String first_name;

private String last_name;

public String getFirst_name() {
    return first_name;
}

public void setFirst_name(String first_name) {
    this.first_name = first_name;
}

public String getLast_name() {
    return last_name;
}

public void setLast_name(String last_name) {
    this.last_name = last_name;
}

Answer 3

这是因为 pojo_for_users.Datum 类中的属性名称与 API 中的 JSON 属性名称不完全匹配。您需要使用“first_name”而不是“firstName”，以及“last_name”而不是“lastName”。或者您可以使用注释来指定您希望使用的名称和 API 使用的名称：

@SerializedName("last_name") //API uses this
private String lastName;   // but in your code you can use this