How can I write a code that triggers when clicking on Save button

Question

I want to hide certain fields inside my tracking list, if the login user is not part of the “Managers” group.
To do so I want to add the following Page-load code inside a web part :-
using (SPSite site = new SPSite(SPContext.Current.Site.Url))
using (SPWeb web = site.OpenWeb())
{SPGroup group = site.Groups["Managers"];
bool isUser = site.IsCurrentUserMemberOfGroup(group.ID);
if (isUser)
{textbox.Visible=false;}}
And the following custom code that triggers when saving the form :-
using (SPSite site = new SPSite(SPContext.Current.Site.Url))
using (SPWeb web = site.OpenWeb())
SPList list = web.Lists["ListName"];web.AllowUnsafeUpdates = true;
SPListItem item = list.Items[SPContext.Current.ListItem.UniqueId];
txtTitle.Text = item["Title"] as string;item.Update();web.AllowUnsafeUpdates = false;
But I am not sure where exactly I should add the custom code for the save button ? I tried writing it inside the Oninit method , but I got many errors as shown below:-
So can anyone advice how i should write the web part to include the Page load & the custom save button code?
second question in general is my above approach considered valid , i mean to hide/show list columns using web parts ?

Answer 1

Hi,
According to your post, my understanding is that you want to hide/show list columns based on specify the permission for Users, SharePoint Groups or Active Directory Groups.
Here is a solution from CodePlex for your reference:
SharePoint 2013 Column & View Permission
https://sp2013columnpermission.codeplex.com/
Best Regards
Dennis Guo
TechNet Community Support