我现在写了一个app.config文件如下：<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="Test1" type="System.Configuration.SingleTagSectionHandler"/>
    <section name="Test2" type="System.Configuration.DictionarySectionHandler"/>
    <section name="Test3" type="System.Configuration.NameValueSectionHandler" />
  </configSections>
  <appSettings>
   
  </appSettings>
  <Test1 setting1="Hello" setting2="World"/>
  <Test2>
    <add key="Hello" value="World" />
  </Test2>
  <Test3>
    <add key="Hello" value="World" />
  </Test3>
</configuration>
我现在能读 ，但是我想写写不了，改不了test1中的值，请问各位高人怎么写啊？下面是我的读方法：System.Collections.IDictionary IDTest1 = (System.Collections.IDictionary)System.Configuration.ConfigurationManager.GetSection("Test1");
            string str = (string)IDTest1["setting1"] + " " + (string)IDTest1["setting2"];
            MessageBox.Show(str);

那具体怎么写啊？

XML又怎么写啊？请指教！