Question

using System;
using System.Data;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Linq;

namespace ProiectBDD
{
    public partial class AdaugaIntrebari : UserControl
    {
        private string connstring;

        public string Connstring
        {
            get { return connstring; }
            set { connstring = value; }
        }

        public AdaugaIntrebari(string p_connstring)
        {
            connstring = p_connstring;
            InitializeComponent();
            IncarcaCategorii();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (enumerator.MoveNext())
            {
                label1.Text = enumerator.Current.Categorie;
            }
        }

        public void IncarcaCategorii()
        {
            DataClasses1DataContext dc = new DataClasses1DataContext();
            var q = from a in dc.GetTable<Categorii>()
                    select a;
            var enumerator = q.AsEnumerable().GetEnumerator();
        }
    }
}

I get Name enumerator does not exist in current context error in my button event handler
method.

Answer 1

button1_Click doesn’t know about enumerator because it exists only in IncarcaCategorii
you need to make it a class field

using System;
using System.Data;
using System.Windows.Forms;
using System.Linq;

namespace ProiectBDD
{
    public partial class AdaugaIntrebari : UserControl
    {
        private string connstring;
        private IEnumerator<DataRow> _enumerator;

        public string Connstring
        {
            get { return connstring; }
            set { connstring = value; }
        }

        public AdaugaIntrebari(string p_connstring)
        {
            connstring = p_connstring;
            InitializeComponent();
            IncarcaCategorii();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (_enumerator == null) return;

            if (enumerator.MoveNext())
            {
                label1.Text = _enumerator.Current.Categorie;
            }
        }

        public void IncarcaCategorii()
        {
            DataClasses1DataContext dc = new DataClasses1DataContext();
            var q = from a in dc.GetTable<Categorii>()
                    select a;
            _enumerator = q.AsEnumerable().GetEnumerator();

        }
    }
}