ConfigurationManager.AppSettings Property

在app.config文件中添加如下配置

 <appSettings>
    <add  key="Server" value="127.0.0.1"/>
    <add  key="Port" value="2020"/>
  </appSettings>

访问方式(需要添加System.Configuration.dll的引用)

  string server = ConfigurationManager.AppSettings["Server"];
  int port = Convert.ToInt32(ConfigurationManager.AppSettings["Port"]);

https://msdn.microsoft.com/en-us/library/system.configuration.configurationmanager.appsettings(v=vs.110).aspx

Gets the AppSettingsSection data for the current application's default configuration.

Namespace:   System.Configuration
Assembly:  System.Configuration (in System.Configuration.dll)

public static NameValueCollection AppSettings { get; }

Property Value

Type: System.Collections.Specialized.NameValueCollection

Returns a NameValueCollection object that contains the contents of the AppSettingsSection object for the current application's default configuration.

Exceptions

ConfigurationErrorsException

Could not retrieve a NameValueCollection object with the application settings data.

Remarks

A AppSettingsSection object contains the contents of the configuration file's appSettings section.

The first example shows a simple console application that reads application settings, adds a new setting, and updates an existing setting.

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");
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <appSettings>
    <add key="Setting1" value="May 5, 2014"/>
    <add key="Setting2" value="May 6, 2014"/>
  </appSettings>
</configuration>

How to find path of active app.config file?

Try this

AppDomain.CurrentDomain.SetupInformation.ConfigurationFile

Hope it helps