Add Microsoft.Sharepoint.dll as a reference in your Project.
Use the following namespace for your Project to utilise the Sharepoint classes, properties and methods.
Once you add the reference and namespace properly, intellisense will show you all the classes and methods properly.
mySite = new SPSite("http://Test-Sample:123/"); //You have to specify your site here.
SPWeb myweb = mySite.AllWebs["IT"]; //You have to speify the subsite here.
myweb.AllowUnsafeUpdates = true; //It will allow you to update listitem or List or anything from your code.
myweb.Update(); //It will update the web.
This code will be hardcoded. If you don't want to hardcode you can use the following code snippet
string Subsite = Request.QueryString["Subsite"]
mySite = new SPSite(this.Page.Request.Url.ToString());
SPWeb myweb = mySite.AllWebs[Subsite];
myweb.AllowUnsafeUpdates = true;
The above example is a good practice to implement it to your Project. In this project instead of subsite hardcoding, i used querystring to fetch the subsite from other forms. Based on the subsite value it will connect to your subsite.
10 years ago