下面是我们想要拼接出来的JSON字符串，返回给前台
{"success":"true","msg":"","data":[{"macName":"正面预拼装机","state":1.0},{"macName":"正面拼板压力架","state":1.0},{"macName":"板片翻身系统","state":1.0},{"macName":"反面预拼装机","state":1.0},{"macName":"反面拼板压力架","state":1.0},{"macName":"划线喷码机","state":0.0},{"macName":"纵骨焊接安装辊道","state":0.0},{"macName":"纵骨焊接机","state":1.0},{"macName":"T排焊接安装辊道","state":0.0}]}
想看拼接后的JSON格式，这里可以推荐一个网站:
https://www.json.cn/
之前都是用StringBuider手动拼接出JSON数据，拼出来的结果还容易错，下面推荐一个简单方式
首先，我们把JSON数组创建实体类，那么问题来了，这个实体类如何创建，这里推荐一个网站：
http://www.bejson.com/convert/json2csharp/
，只需要将JSON格式放入，就会帮我们自动转成实体类
实体类也比较简单，用到了List集合存放对象，下面Demo演示
public class MacState
/// <summary>
/// 请求状态
/// </summary>
public string success { get; set; }
/// <summary>
/// 错误信息
/// </summary>
public string msg { get; set; }
/// <summary>
/// JSON数组
/// </summary>
public List<MacStateData> data { get; set; }
public class MacStateData
/// <summary>
/// 设备名称
/// </summary>
public string macName { get; set; }
/// <summary>
/// 运行状态 运行/停止（1/0）
/// </summary>
public decimal state { get; set; }
函数(标红色的注意！！！)
/// <summary>
/// 设备状态情况
/// </summary>
/// <returns>JSON数组</returns>
[WebMethod(Description ="设备状态")]
public string GetMacState()
MacState obj = new MacState();
DateTime NowDate = DateTime.Now;
DataTable dt_his_count = new DataTable();
DataTable dt_mac_state = new DataTable();
int max_count = 200000;
string add_his_sql = "INSERT INTO EMES_MAC_STATE_PORT_HIS (DEF_DATE) VALUES (TO_DATE('{0}','YYYY-MM-DD HH24:MI:SS'))";
DbUtil.ExecuteSql(string.Format(add_his_sql, NowDate));
string query_his_sql = "SELECT COUNT(*) FROM EMES_MAC_STATE_PORT_HIS";
dt_his_count = DbUtil.QueryDT(query_his_sql);
if (Convert.ToDecimal(dt_his_count.Rows[0][0]??"0")>max_count) //接口日志超过20W条，自动删除
string del_sql = "DELETE FROM EMES_MAC_STATE_PORT_HIS";
DbUtil.ExecuteSql(del_sql);
string query_mac_state_sql = "SELECT MAC_NAME,STATE FROM EMES_MAC_STATE";
dt_mac_state = DbUtil.QueryDT(query_mac_state_sql);
if (dt_mac_state.Rows.Count > 0)
obj.success = "true";
obj.msg = "";
obj.data = new List<MacStateData>(); //实例化JSON数组，不实例化要报错
for (int i = 0; i < dt_mac_state.Rows.Count; i++)
MacStateData objData = new MacStateData(); //实例化JSON数组对象，用于添加JSON数组集合
objData.macName = dt_mac_state.Rows[i]["MAC_NAME"].ToString();
objData.state = Convert.ToDecimal(dt_mac_state.Rows[i]["STATE"] ?? "0");
obj.data.Add(objData); //添加JSON数组集合
string res = JsonConvert.SerializeObject(obj); //转JSON数组，演示用，下面讲方法使用
return JSONHelper.ToJSON(obj); //调用的封装函数，不用管，我们将上面的方式
obj.success = "false";
obj.msg = "当前无数据信息,请稍后再试!";
obj.data = new List<MacStateData>();
return JSONHelper.ToJSON(obj);
catch (Exception ex)
obj.success = "false";
obj.msg = ex.Message;
obj.data = new List<MacStateData>();
return JSONHelper.ToJSON(obj);
注：将对象转JSON数组，我们需要引入外部类库:Newtonsoft.Json.dll，没有的小伙伴请到我另外一篇博客下载：https://www.cnblogs.com/chenyanbin/p/11200415.html
引入命名空间：
using Newtonsoft.Json;
方法使用：
JsonConvert.SerializeObject(实体类对象)
JSON数组
