Why we shouldn't use SPWeb witryna = SPContext.Current.Web;

Question

How should change a code to use another conect to site in Sharepoint. Which code, to change SPWeb witryna = SPContext.Current.Web;

Here is my examplary code:

           protected void Button3_Click(object sender, EventArgs e)
            {
                SPWeb witryna = SPContext.Current.Web;
                SPList oList = witryna.Lists["Szczegoly"];
               // SPListItemCollection elementyDoUsuniecia = oList.Items;
                string FullQuery = "<Where><And><Eq><FieldRef Name='{0}' /><Value Type='DateTime'>{1}</Value></Eq><Eq><FieldRef Name='Pracownik' /><Value Type='Text'>{2}</Value></Eq></And></Where>";
                string dateISO = SPUtility.CreateISO8601DateTimeFromSystemDateTime(Convert.ToDateTime(TextBox4.Text).ToUniversalTime().AddHours(2.0));
                var query1 = new SPQuery();
                query1.Query = String.Format(FullQuery, "Dzien", dateISO, DropDownList1.SelectedItem.Text);
                query1.ViewFields = "<FieldRef Name='Dzien' /><FieldRef Name='Pracownik' />";
                SPListItemCollection elementyDoUsuniecia = witryna.Lists["Szczegoly"].GetItems(query1);

                for (int intIndex = elementyDoUsuniecia.Count - 1; intIndex > -1; intIndex--)
                {
                    if (Convert.ToDateTime(elementyDoUsuniecia[intIndex]["Dzien"]).ToShortDateString() == Convert.ToDateTime(TextBox4.Text).ToShortDateString() && elementyDoUsuniecia[intIndex]["Pracownik"].ToString() == DropDownList1.SelectedValue)
                    {
                        elementyDoUsuniecia.Delete(intIndex);
                    }
                }
            }

Getting a error: Attempted to use an object that has ceased to exist. (Exception from HRESULT: 0x80030102 (STG_E_REVERTED)) Please help.

Why better to use:

            using (SPSite siteCollection = new SPSite(SPContext.Current.Web.Url))
            using (SPWeb witryna = siteCollection.OpenWeb())

Answer 1

Current Site
If you're going to work on the site where your code is running (could be web part on a page) then you should use SPContent.Current.Web and not to dispose it.

So don't do this:

var web = SPContext.Current.Web;
// some code
web.Dispose(); // DONT DO THIS

or

using (var web = SPContext.Current.Web) // DON'T DO THIS
{
  // some code
}

as this is the exact same as (just syntactical sugar implemented by the C# compiler)

try 
{
  var web = SPContext.Current.Web;
  // some code
}
finally
{
  web.Dispose(); // DONT DO THIS
}

Same Site Collection
If you're going to work on another site the the same site collection then you should use something like:

using (var web = SPContext.Current.Site.OpenWeb("URL_OF_SITE"))
{
  // Your code
}

I.e. get site from current SPSite object and remember to dispose it.

Other Site Collection
If you're going to work on a site which may not be in the same site collection then you should use something like:

using (var site = new SPSite("URL_OF_SITE"))
  using (var web = site.OpenWeb())
  {
    // Your code
  }

I.e. Get site collection and then get site from that remember to dispose both.