无法为 Product.class 调用无参数构造函数

Question

我在我的 android 应用程序中使用 GSON 和 Volley 库进行网络连接，但是在使用 Gson 将 Json 响应转换为 Model 类时，出现以下错误：

88-2006/ E/Volley﹕ [121] NetworkDispatcher.run: Unhandled exception java.lang.RuntimeException: Unable to invoke no-args constructor for class [Lcom.example.model.Product;. Register an InstanceCreator with Gson for this type may fix this problem.
    java.lang.RuntimeException: Unable to invoke no-args constructor for class [Lcom.example.model.Product;. Register an InstanceCreator with Gson for this type may fix this problem.

这些是我正在使用的 POJO 类： 产品.java

public class Product {

    private String status;

    private List<Result> results = new ArrayList<Result>();

    private Pagination pagination;
    public Product(){}

    // getters and setters
}

分页.java

public class Pagination {

    private String first;

    private String previous;

    private String next;

    private String last;
    public Pagination(){}
}

结果.java

public class Result {

    private String id;

    private Properties properties;
    public Result{}

}

Properties.java

public class Properties {

    private String qbcode;

    private String name;

    private String purchasedate;

    private String vendor;

    private String thumbnail;
    public Properties(){}
}

我已经解决了类似这样的现有问题，根据我发现的答案，我在所有类中添加了 no arg 构造函数，但我仍然收到错误请帮助我解决这个问题

Json 字符串：

{
  "status" : "OK",
  "results" : [ {
    "id" : "IzIzOjE=",
    "properties" : {
      "qbcode" : "IN-1-1",
      "name" : "Test Name",
      "purchasedate" : "2015-05-21",
      "vendor" : "Test Vendor",
      "thumbnail" : "http://en.wikipedia.org/static/images/project-logos/enwiki.png"
    }
  }, {
    "id" : "IzIzOjI=",
    "properties" : {
      "qbcode" : "IN-1-2",
      "name" : "Test Name",
      "purchasedate" : "2015-05-21",
      "vendor" : "Test Vendor",
      "thumbnail" : "http://en.wikipedia.org/static/images/project-logos/enwiki.png"
    }
  }, {
    "id" : "IzIzOjM=",
    "properties" : {
      "qbcode" : "IN-1-3",
      "name" : "Test Name",
      "purchasedate" : "2015-05-21",
      "vendor" : "Test Vendor",
      "thumbnail" : "http://en.wikipedia.org/static/images/project-logos/enwiki.png"
    }
  },{
    "id" : "IzIzOjU=",
    "properties" : {
      "qbcode" : "IN-1-5",
      "name" : "Test Name",
      "purchasedate" : "2015-05-21",
      "vendor" : "Test Vendor",
      "thumbnail" : "http://en.wikipedia.org/static/images/project-logos/enwiki.png"
    }
  } ],
  "pagination" : {
    "first" : "/list?size=20",
    "previous" : "/list?start=IzIzOjE=&size=20",
    "next" : "/list?start=IzIzOjQx&size=20",
    "last" : "/list?start=IzIzOjYx&size=20"
  }
}

Answer 1

为所有类添加默认构造函数。示例：

public class Product{

    public Product(){
    }

}

Answer 2

问题解决了，我对 Gson 做了一个愚蠢的调用，因为我正在获取一个包含其他类（Result.class 等）列表的 Product 类，但我正在将 Product[].class 发送到 Gson 以进行转换，因此它抛出了异常.

Answer 3

您的模型具有私有属性，您必须为其创建 setter 或创建具有所有参数的构造函数，如下所示：

public class Product {

    private String status;
    private List<Result> results = new ArrayList<Result>();
    private Pagination pagination;

    public void setStatus(String status) {
        this.status = status;
    }

    public void setResults(List<Result> results) {
        this.results = results;
    }

    public void setPagination(Pagination pagination) {
        this.pagination = pagination;
    }
}

或

public class Product {

    private String status;
    private List<Result> results = new ArrayList<Result>();
    private Pagination pagination;

    public Product(String status, List<Result> results, Pagination pagination) {
        this.status = status;
        this.results = results;
        this.pagination = pagination;
    }

}