The .NET Page class contains two methods ResolveUrl and ResolveClientUrl which are at first glance looks same. They both took same relative URL and returns browser friendly URl. So why 2 function to do the same job? Though their functionality is same but their way of returning client brower relative url makes the huge difference.ResolveClientUrl returns a path relative to the current page which user currently browsing, and ResolveUrl returns a path relative to the site root that is configured as root in IIS.
Lets Consider this structure:
Now from above example root of the IIS directory is ROOT, and all other directory is under this root. Now from MyAccount->default.aspx tries to access Images->mypic.png.
ResolveUrl will do top to bottom parsing to find the resource, on other hand
ResolveClientUrl will do bottom up parsing to find the same resource.
Difference betwwen this two is very visible if you hoste your web app under a shared hosting under a subdomain. For example you host your MY_SITE app under www.example.com subdomain, and your physical file path is
example.com\www\MY_SITE under IIS directory. So under this you placed your file structure given above. Now for any link if you set
watch out the URL in browser status bar you will see www.example.comwww/MY_SITE/MyAccount/default.aspx, because
ResolveUrl will parse from top root domain for this resource, so it took full path from root for that specific resource. On other hand
ResolveClientUrl can solve this problem, this will parse from browsers present location to up towards the root so find the specific resource path.