In my previous post, Get a list of all the Shared users for a ListItem/Document of SharePoint List, I had described how to get the list of all the SharePoint users with whom a given Document Library item, has been shared. Now, in this post, I am going to Share an existing ListItem with a different SP user using CSOM.This works in the following 2 simple steps:

1. Get the user(principal) with whom the item has to be shared.
2. Next, get/create the RoleDefinition which will have various Permission Rights for the user.

The 2nd point is important. SP has already defined various RoleDefinitions that we can use for our purpose like, Administrator, ContentEditior, Read, etc. So we can either use any one of them or can even create our own custom RoleDefinition. I am going to demonstrate both the functionalities here.

First get the User and the ListItem which is to be shared

ClientContext ctx = new ClientContext("targetURL");
ctx.Credentials = new SharePointOnlineCredentials(userName, passWord);

ctx.Load(ctx.Web);
SP.ListCollection listCol = web.Lists;
ctx.Load(listCol);

SP.List list = listCollection.GetByTitle("ListTitle");

SP.CamlQuery camlQuery = new SP.CamlQuery();
camlQuery.ViewXml = "";

SP.ListItemCollection listItemCollection = list.GetItems(camlQuery);
ctx.Load(listItemCollection);

ctx.ExecuteQuery();

//get the user you want to share the current item
User currentUser = ctx.Web.EnsureWeb("memberLoginName")
SP.ListItem listItem = listItemCollection.FirstOrDefault(t => t.DisplayName == "WordFile");
ctx.Load(listItem,
    li => li.HasUniqueRoleAssignments,
    li => li.RoleAssignments.Include(
        p => p.Member,
        p => p.RoleDefinitionBindings.Include(
            s => s.Name)));
ctx.Load(currentUser);
            
ctx.ExecuteQuery(); 

Share with User with Existing RoleDefinition

RoleDefinitionCollection roleDefCol = ctx.Web.RoleDefinitions;

ctx.Load(roleDefCol, r => r.Include(p => p.Name));
ctx.ExecuteQuery();

RoleDefinitionBindingCollection rDefBindCol = new RoleDefinitionBindingCollection(ctx);

//Could be Edit, Read, Contribute, etc.
string roleDefName = "Edit";
RoleDefinition rDef = roleDefCol.FirstOrDefault(p => p.Name == roleDefName);

if(rDef != null)
{
    //Add the current binding to the seleted listItems RoleAssignments
    rDefBindCol.Add(rDef);
}

ctx.ExecuteQuery();

Console.WriteLine("SharePoint Role Assigned successfully.");

Share with User with new Custom RoleDefinition

Site collSite = ctx.Site;

// Set up permissions.
BasePermissions permissions = new BasePermissions();
permissions.Set(PermissionKind.ViewListItems);
permissions.Set(PermissionKind.AddListItems);
permissions.Set(PermissionKind.EditListItems);
permissions.Set(PermissionKind.DeleteListItems);

// Create a new role definition.
RoleDefinitionCreationInformation rdcInfo = new RoleDefinitionCreationInformation();
rdcInfo.Name = "Manage List Items";
rdcInfo.Description = "Allows a user to manage this list items";
rdcInfo.BasePermissions = permissions;
RoleDefinition roleDef = collSite.RootWeb.RoleDefinitions.Add(rdcInfo);

// Create a new RoleDefinitionBindingCollection object.
RoleDefinitionBindingCollection collRDB = new RoleDefinitionBindingCollection(ctx);
// Add the role to the collection.
collRDB.Add(roleDef);

// Break permissions so its permissions can be managed directly.
listItem.BreakRoleInheritance(true, false);

// Get the RoleAssignmentCollection for the target listItem.
RoleAssignmentCollection collRoleAssign = listItem.RoleAssignments;
// Add the user to the target listItem and assign the user to the new //RoleDefinitionBindingCollection.
RoleAssignment rollAssign = collRoleAssign.Add(currentUser, collRDB);

ctx.ExecuteQuery();

Console.WriteLine("Custom Role Assigned successfully.");