Dictionary<string, string> myDic = new Dictionary<string, string>();
myDic.Add("aaa", "111");
myDic.Add("bbb", "222");
myDic.Add("ccc", "333");
myDic.Add("ddd", "444");
//如果添加已经存在的键，add方法会抛出异常
try
{
 myDic.Add("ddd","ddd");
}
catch (ArgumentException ex)
{
 Console.WriteLine("此键已经存在：" + ex.Message);
}
//解决add()异常的方法是用ContainsKey()方法来判断键是否存在
if (!myDic.ContainsKey("ddd"))
{
 myDic.Add("ddd", "ddd");
}
else
{
 Console.WriteLine("此键已经存在：");
 
}
 
//而使用索引器来负值时，如果建已经存在，就会修改已有的键的键值，而不会抛出异常
myDic ["ddd"]="ddd";
myDic["eee"] = "555";
 
//使用索引器来取值时，如果键不存在就会引发异常
try
{
 Console.WriteLine("不存在的键""fff""的键值为：" + myDic["fff"]);
}
catch (KeyNotFoundException ex)
{
 Console.WriteLine("没有找到键引发异常：" + ex.Message);
}
//解决上面的异常的方法是使用ContarnsKey() 来判断时候存在键，如果经常要取健值得化最好用 TryGetValue方法来获取集合中的对应键值
string value = "";
if (myDic.TryGetValue("fff", out value))
{
 Console.WriteLine("不存在的键""fff""的键值为：" + value );
}
else
{
 Console.WriteLine("没有找到对应键的键值");
}
 
//下面用foreach 来遍历键值对
//泛型结构体 用来存储健值对
foreach (KeyValuePair<string, string> kvp in myDic)
{
 Console.WriteLine("key={0},value={1}", kvp.Key, kvp.Value);
}
//获取值得集合
foreach (string s in myDic.Values)
{
 Console.WriteLine("value={0}", s);
}
//获取值得另一种方式
Dictionary<string, string>.ValueCollection values = myDic.Values;
foreach (string s in values)
{
 Console.WriteLine("value={0}", s);
}

<?xml version="1.0" encoding="UTF-8"?>
<data>
 <resource key="123">foo</resource>
 <resource key="456">bar</resource>
 <resource key="789">bar</resource>
</data>
i want to put this into a Dictionary (sorted) as key value pairs. i.e: 123:foo, 456:bar...etc
the keys are unknown.
 
string s = "<data><resource key=/"123/">foo</resource><resource key=/"456/">bar</resource><resource key=/"789/">bar</resource></data>";
 XmlDocument xml = new XmlDocument();
 xml.LoadXml(s);
 XmlNodeList resources = xml.SelectNodes("data/resource");
 SortedDictionary<string,string> dictionary = new SortedDictionary<string,string>();
 foreach (XmlNode node in resources){
 dictionary.Add(node.Attributes["key"].Value, node.InnerText);
 }

linq to xml:
var xml = XDocument.Load(...);
var sequence = from e in xml.Root.Elements() 
let key = (string)e.Attribute("key")
order by key
select new { 
 Key = key, 
 Value = (string)e 
};