如何从 [Object] android 获取数据

Question

我从我的Express API 电话中收到此response。

回复如下：

{
    "responseData": [{
        "unitNames": [
            "Matrices",
            "Complex Numbers"
        ],
        "subject": "maths",
        "unitTopics": {
            "1": [{
                    "topicName": "1.1 Introduction",
                    "topicURL": ""
                },
                {
                    "topicName": "1.2 Square Matrix",
                    "topicURL": ""
                }

            ],
            "2": [{
                    "topicName": "2.1 Numbers",
                    "topicURL": ""
                }

            ]
        }
    }]
}

我通过在 Android 中使用 Retrofit 得到了响应。它很好用。但它无法解析 Objects

这是我在 Android 端的问题。

{
        "responseData": [{
            "unitNames": [
                "Matrices",
                "Complex Numbers"
            ],
            "subject": "maths",
            "unitTopics": {
                "1": [[Object],
                    [Object]
    
                ],
                "2": [[Object]
    
                ]
            }
        }]
    }

它显示对象而不是我的数据。如何解决这个问题

这是代码：

System.out.println(response.body().getResponseData())
String received_data = response.body().getResponseData();
received_data_sub_units_topics_json = new JSONArray("["+received_data+"]");
System.out.println("MAIN2 "+received_data_sub_units_topics_json);

转换成jsonarray后是这样的，

{
        "responseData": [{
            "unitNames": [
                "Matrices",
                "Complex Numbers"
            ],
            "subject": "maths",
            "unitTopics": {
                "1": [["Object"],
                    ["Object"]
    
                ],
                "2": [["Object"]
    
                ]
            }
        }]
    }

请帮我解决一些问题

Answer 1

对于 json，我总是使用库 com.fasterxml.jackson。

你也可以使用org.json.JSONArray、org.json.JSONObject。

以下是每个示例： 1-杰克逊

对于实现这个（有点长，但你会将它转换为 java 类，因此，你可以编辑值并比使用 JSONObject 更容易地获取它），你必须创建具有相同结构的类比你的json：

public class principalClass {
     ArrayList<ResponseData> responseData;  
     ...
     //Getters, setters and constructors
}

public class ResponseData {
    public ArrayList<String> unitNames;
    public String subject;
    public UnitTopics unitTopics;
    ...
    //Getters, setters and constructors
}

public class UnitTopics {
    public ArrayList<Topics> first;
    public ArrayList<Topics> second;
    ...
    //Getters, setters and constructors
}

public class Topics {
    public String topicName;
    public String topicURL;
    ...
    //Getters, setters and constructors
}

类似的东西，然后你使用jackson将你的json传递给你的class principalClass：

ObjectMapper obj= new ObjectMapper();
PrincipalClass principal= obj.readValue(json, PrincipalClass.class);

第二种可能性是将值转换为 JSONArray 和 JSONObject：

JSONObject bodyJSON = new JSONObject(json);

JSONArray responseData = bodyJSON.getJSONArray("responseData");

JSONArray unitNames= responseData.getJSONArray(0);
JSONObject subject= responseData.getJSONObject(1);
...

如果你愿意，你可以循环一个 JSONArray：

for (int i = 0; i < unitNames.length(); i++) {     
     String element = unitNames.getString(i);     
}

Answer 2

您可以使用带有改造的 gson 转换器将您的 json 数据转换为 java 对象模型类

implementation 'com.squareup.retrofit2:converter-gson:2.4.0'

或者您可以将 json 数据转换为模型类，如

Gson gson = new Gson();
String jsonInString = "{your json data}";
ResponseModel response= gson.fromJson(jsonInString, ResponseModel.class);

Answer 3

您是否尝试过将此 JSON 对象转换为 POJO。 我建议使用： This website

它节省了大量的时间和精力。 这些将是您的模型类：

package com.example.app;

import java.io.Serializable;
import java.util.List;
import javax.annotation.Generated;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;


public class ResponseDatum implements Serializable
{

@SerializedName("unitNames")
@Expose
private List<String> unitNames = null;
@SerializedName("subject")
@Expose
private String subject;
@SerializedName("unitTopics")
@Expose
private UnitTopics unitTopics;


public ResponseDatum() {
}


public ResponseDatum(List<String> unitNames, String subject, UnitTopics unitTopics) {
super();
this.unitNames = unitNames;
this.subject = subject;
this.unitTopics = unitTopics;
}

public List<String> getUnitNames() {
return unitNames;
}

public void setUnitNames(List<String> unitNames) {
this.unitNames = unitNames;
}

public String getSubject() {
return subject;
}

public void setSubject(String subject) {
this.subject = subject;
}

public UnitTopics getUnitTopics() {
return unitTopics;
}

public void setUnitTopics(UnitTopics unitTopics) {
this.unitTopics = unitTopics;
}

}

package com.example.app;

import java.io.Serializable;
import java.util.List;
import javax.annotation.Generated;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class ResponseObject implements Serializable
{

@SerializedName("responseData")
@Expose
private List<ResponseDatum> responseData = null;


public ResponseObject() {
}


public ResponseObject(List<ResponseDatum> responseData) {
super();
this.responseData = responseData;
}

public List<ResponseDatum> getResponseData() {
return responseData;
}

public void setResponseData(List<ResponseDatum> responseData) {
this.responseData = responseData;
}

}


package com.example.app;

import java.io.Serializable;
import java.util.List;
import javax.annotation.Generated;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class UnitTopics implements Serializable
{

@SerializedName("1")
@Expose
private List<com.example.app._1> _1 = null;
@SerializedName("2")
@Expose
private List<com.example.app._2> _2 = null;



public UnitTopics() {
}


public UnitTopics(List<com.example.app._1> _1, List<com.example.app._2> _2) {
super();
this._1 = _1;
this._2 = _2;
}

public List<com.example.app._1> get1() {
return _1;
}

public void set1(List<com.example.app._1> _1) {
this._1 = _1;
}

public List<com.example.app._2> get2() {
return _2;
}

public void set2(List<com.example.app._2> _2) {
this._2 = _2;
}

}


package com.example.app;

import java.io.Serializable;
import javax.annotation.Generated;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class _1 implements Serializable
{

@SerializedName("topicName")
@Expose
private String topicName;
@SerializedName("topicURL")
@Expose
private String topicURL;




public _1() {
}


public _1(String topicName, String topicURL) {
super();
this.topicName = topicName;
this.topicURL = topicURL;
}

public String getTopicName() {
return topicName;
}

public void setTopicName(String topicName) {
this.topicName = topicName;
}

public String getTopicURL() {
return topicURL;
}

public void setTopicURL(String topicURL) {
this.topicURL = topicURL;
}

}


package com.example.app;

import java.io.Serializable;
import javax.annotation.Generated;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;


public class _2 implements Serializable
{

@SerializedName("topicName")
@Expose
private String topicName;
@SerializedName("topicURL")
@Expose
private String topicURL;



public _2() {
}


public _2(String topicName, String topicURL) {
super();
this.topicName = topicName;
this.topicURL = topicURL;
}

public String getTopicName() {
return topicName;
}

public void setTopicName(String topicName) {
this.topicName = topicName;
}

public String getTopicURL() {
return topicURL;
}

public void setTopicURL(String topicURL) {
this.topicURL = topicURL;
}

}