Accessing SPList-cross web application, sitecollection and site

There might be some scenario where we might have to access list across site collection. We might have a situation that we have to search for a list across a site collection. We may have to check whether the list is present in any of the site collection or not and if present we may have to do some operation on the list. Below is the code snippet that may be useful in this scenario-
private string GetListvalue()
{
string strVal=string.Empty;
SPSecurity.RunWithElevatedPrivileges(delegate()
{
Uri uri = new Uri(SPContext.Current.Web.Url.ToString());
SPWebApplication webApp = SPWebApplication.Lookup(new Uri("http://" + uri.Host));
if (webApp != null && webApp.Sites != null && webApp.Sites.Count > 0)
{
using (SPWeb web = SPContext.Current.Site.RootWeb)
{
foreach (SPSite site in webApp.Sites)
{
foreach (SPWeb web in site.AllWebs)
{
if (IfListExists(web, "List Name"))
{
SPList lstStore;
SPListItemCollection items;
lstStore = web.GetList(list path);
SPQuery query = new SPQuery();
query.Query = "CAML query";
items = lstStore.GetItems(query);
strVal = items[0]["Column name"].ToString();
}
}
}
}
}
}
});
return strVal;
}
Here I am accessing a sigle column from the first row that will be returned by the query.
The IfListExists() method will use Linq to check whether the list exists or not. Sharepoint don't have any method or properties to check the existance of the list. Another alternative is to use the Extension Methods. Below is the definition of the IfListExists() method-
private static bool IfListExists(SPWeb web, string listName)
{
return web.Lists.Cast().Any(list => string.Equals(list.Title, listName));
}

Thats it.
Hopes it will help. :)