一、前言

　　在项目中，我们习惯使用 ConfigurationManager 来读取一些常量。如链接数据库字符串、一些需配置的数据（微信、QQ、支付宝）等的配置。我们需要把这些数据记录在 app.config 或者 web.config 中。接下来我们具体看一下 ConfigurationManager  ：

二、介绍

　　　命名空间：System.Configuration

　　　程序集： System.Configuration.dll

　　引用：在使用中，如果出现“ 当前上下文中不存在名称：ConfigurationManager ”，你就要检查有没有引用程序集和命名空间了。

　　ConfigurationManager类： 包含属性（AppSettings、ConnectionStrings ）、方法（GetSection、OpenExeConfiguration、OpenExeConfiguration、OpenMachineConfiguration、OpenMappedExeConfiguration、OpenMappedExeConfiguration、OpenMappedMachineConfiguration、RefreshSection）

三、使用

　　通过 AppSettings 来获取数据，简单使用案例：

using System;  
using System.Configuration;  

namespace ConsoleApplication1  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            ReadAllSettings();  
            ReadSetting("Setting1");  
            ReadSetting("NotValid");  
            AddUpdateAppSettings("NewSetting", "May 7, 2014");  
            AddUpdateAppSettings("Setting1", "May 8, 2014");  
            ReadAllSettings();  
        }  

        static void ReadAllSettings()  
        {  
            try  
            {  
                var appSettings = ConfigurationManager.AppSettings;  

                if (appSettings.Count == 0)  
                {  
                    Console.WriteLine("AppSettings is empty.");  
                }  
                else  
                {  
                    foreach (var key in appSettings.AllKeys)  
                    {  
                        Console.WriteLine("Key: {0} Value: {1}", key, appSettings[key]);  
                    }  
                }  
            }  
            catch (ConfigurationErrorsException)  
            {  
                Console.WriteLine("Error reading app settings");  
            }  
        }  

        static void ReadSetting(string key)  
        {  
            try  
            {  
                var appSettings = ConfigurationManager.AppSettings;  
                string result = appSettings[key] ?? "Not Found";  
                Console.WriteLine(result);  
            }  
            catch (ConfigurationErrorsException)  
            {  
                Console.WriteLine("Error reading app settings");  
            }  
        }  

        static void AddUpdateAppSettings(string key, string value)  
        {  
            try  
            {  
                var configFile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);  
                var settings = configFile.AppSettings.Settings;  
                if (settings[key] == null)  
                {  
                    settings.Add(key, value);  
                }  
                else  
                {  
                    settings[key].Value = value;  
                }  
                configFile.Save(ConfigurationSaveMode.Modified);  
                ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name);  
            }  
            catch (ConfigurationErrorsException)  
            {  
                Console.WriteLine("Error writing app settings");  
            }  
        }  
    }  
}

 在文件 App.config 中配置：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
  </startup>
  <appSettings>
    <add key="Setting1" value="May 5,2018"/>
    <add key="Setting2" value="May 5,2017"/>
  </appSettings>
</configuration>

2、通过使用 ConnectionStrings 来获取数据，使用案例

using System;  
using System.Configuration;  
using System.Data.SqlClient;  

namespace ConsoleApplication1  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            ReadUsers();  
        }  

        static void ReadUsers()  
        {  
            var connectionString = ConfigurationManager.ConnectionStrings["Default"].ConnectionString;  
            string queryString = "SELECT Id, Name FROM abpusers;";  
            using (var connection = new SqlConnection(connectionString))  
            {  
                var command = new SqlCommand(queryString, connection);  
                connection.Open();  
                using (var reader = command.ExecuteReader())  
                {  
                    while (reader.Read())  
                    {  
                        Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1]));  
                    }  
                }  
            }  
        }  
    }  
}

在 App.config 中配置数据库链接字符串：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
  </startup>
  <appSettings>
    <add key="Setting1" value="May 5,2018"/>
    <add key="Setting2" value="May 5,2017"/>
  </appSettings>

  <connectionStrings>
    <add name="Default" connectionString="Server=127.0.0.1; Database=CityManage; Trusted_Connection=False; Uid=root; pwd=zxx123456;" providerName="System.Data.SqlClient" />
    <add name="Abp.Redis.Cache" connectionString="localhost" />
  </connectionStrings>

</configuration>

简单小节，资源来源于：官网教程

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