according to .NET Framework documentation, "... The Uri class stores only absolute URIs (for example, "http://www.contoso.com/index.htm"). Relative URIs (for example, "/new/index.htm") must be expanded with respect to a base URI so that they are absolute. ..."
"...
The Uri class stores only absolute URIs (for example, "http://www.contoso.com/index.htm"). Relative URIs (for example, "/new/index.htm") must be expanded with respect to a base URI so that they are absolute.
..."
这里搜索keyword为url可以找到你要的答案
还是有些模糊