HTML标签转换函数

public string ChangeString(string str)
{
//str含有HTML标签的文本
str = str.Replace("<","&lt;");
str = str.Replace(">","&gt;");
str = str.Replace(" ","&nbsp;");
str = str.Replace("\n","<br>");
str = str.Replace("&","&amp;");
return str;
}