SPListItem field resets to null after calling Update

Question

I use SharePoint 2013 with the following code:

SPListItem listItem;
...
listItem["MyCol"] = " "; // Space character.
Console.WriteLine($"listItem[\"MyCol\"] = {listItem["MyCol"]}"); // Here i see the space character.
listItem.Update();
Console.WriteLine($"listItem[\"MyCol\"] = {listItem["MyCol"]}"); // Here value is became null.

Looks like issue reproduces only for space character.

Answer 1

you have to execute your query with clientContext.ExecuteQuery()

ListItem oListItem = oList.AddItem(itemCreateInfo);
oListItem["Title"] = "My New Item!";
oListItem.Update();
clientContext.ExecuteQuery(); 

Answer 2

According to the below explanation, you need to call ExecuteQuery() to take effect of Update() call.

To set most list item properties, you can use a column indexer to make an assignment, and call the Update() method so that changes will take effect when you call ExecuteQuery() or ExecuteQueryAsync(ClientRequestSucceededEventHandler, ClientRequestFailedEventHandler).

Source: Updating a list item.

Try your code like below:

string siteUrl = "http://MyServer/sites/MySiteCollection";

ClientContext clientContext = new ClientContext(siteUrl);
SPListItem listItem;
...
listItem["MyCol"] = " "; // Space character.
Console.WriteLine($"listItem[\"MyCol\"] = {listItem["MyCol"]}"); // Here i see the space character.
listItem.Update();

clientContext.ExecuteQuery(); //Call this method before writing the value to Console.

Console.WriteLine($"listItem[\"MyCol\"] = {listItem["MyCol"]}"); // Here value is became null.

Answer 3

In case, if the current user does not have appropriate rights then also it won't allow you to update. Kindly keep your code enclosed within RunWithElevatedPrivileges which uses System User Account

SPSecurity.RunWithElevatedPrivileges(delegate(){ //your code  });