desperate people take desperate measures.

这个在codeproject上看的的一个解决方案，拿来试试，不知道为什么不成功。
原文：http://www.codeproject.com/KB/dotnet/dllappconfig.aspx?msg=2823743#xx2823743xx

需求是：
给Dll添加一个Config文件是不行的. 是因为.NET一般只允许将Running application和一个Config绑定。
而程序一旦启动，The .NET Framework reads the application configuration file into a static hashtable whenever the application domain is first referenced. Once it is read, it cannot be reread or modified.

作者n10sive研究了System.Dll，发现
1.  修改ConfigurationSettings class 的静态变量"_configurationInitialized" 为false， 就可以“欺骗”.NET Framework, config file还没有读入。
2. null out the "_configSystem". 使得.NET Framework将config读入内存。

并且作者给出了包装好config参数的类，
如果你在程序中new这个类出来后，将会修改程序默认引用的myproject.vshost.exe.Config为mydll.dll.config


下面是我的理解，找他的方法做了一下，没有成功。
I have a Dll "MyDll.dll", with a "MyDll.dll.config" file:
And I have an App project,
Using this line to get the file path:
string str = MyDllConfig.ConnectionString();
but, when I debug into

MyDll.dll.Config
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key ="AlgorithmConfigFile" value="CashAcceptType.xml"/>
  </appSettings>
  <connectionStrings/>
</configuration>

 

Code
public static string ConnectionString()
        {
            string cstr;
            using (new MyDllConfig())
            {
                string str = AppDomain.CurrentDomain.GetData("APP_CONFIG_FILE").ToString();
                cstr = ConfigurationManager.AppSettings["AlgorithmConfigFile"];
            }
            return cstr;
        }

"str" is MyDll.config which is under my execute app path.
but "cstr" is null!

I don't know why
ConfigurationManager.AppSettings["AlgorithmConfigFile"];
can't get the value "CashAcceptType.xml"

园子里是否有兄弟闲的有空，玩玩这个方法，呵呵。

PS：最后发现作者原来已经是CTO了，1977年就开始玩计算机软硬件了，呵呵。

Code
internal class MyDllConfig : IDisposable
{
    private string _oldConfig;
    private bool _libCompat;
    private const string _newConfig = "mydll.dll.config";
    // don't forget to rename this!!

    internal MyDllConfig()
    {
        _libCompat = Assembly.GetAssembly(typeof(
          ConfigurationSettings)).GetName().Version.ToString().
          CompareTo("2.0.0.0") == 0;
        _oldConfig = AppDomain.CurrentDomain.GetData(
               "APP_CONFIG_FILE").ToString();
        Switch(_newConfig);
    }
    protected void Switch(string config)
    {    
        if ( _libCompat )
        {
            AppDomain.CurrentDomain.SetData("APP_CONFIG_FILE",config);
            FieldInfo fiInit = typeof(
                System.Configuration.ConfigurationSettings).GetField(
                    "_configurationInitialized",
                    BindingFlags.NonPublic|BindingFlags.Static);
            FieldInfo fiSystem = typeof(
                System.Configuration.ConfigurationSettings).GetField(
                    "_configSystem",BindingFlags.NonPublic|BindingFlags.Static);
            if ( fiInit != null && fiSystem != null )
            {
                fiInit.SetValue(null,false);
                fiSystem.SetValue(null,null);
            }
        }
    }

    public void Dispose()
    {
        Switch(_oldConfig);
    }

    public static string ConnectionString()
    {
        string cstr;
        using ( new MyDllConfig() )
        {
            cstr = ConfigurationSettings.AppSettings["ConnectionString"];
        }
        return cstr;
    }
}