How to get SharePoint group only for peoplepicker in C#?

Question

I have create a SharePoint 2013 peoplepicker field in an application page and want to show the SharePoint group only..

code: C#

    using (SPSite site = new SPSite("http://site/subsite"))
    { 
        SPUser user = null;
        ArrayList resolvedEntities = peoplePicker.ResolvedEntities;
        foreach (PickerEntity entity in resolvedEntities)
        {
            string loginName = entity.Key;
            user = site.RootWeb.EnsureUser(loginName);
            break;
        }
    }

ASPX:

      <SharePoint:ClientPeoplePicker
                Required="true"
                ValidationEnabled="true"
                ID="peoplePicker"
                runat="server"
                InitialHelpText="<%$Resources:wss,aclinv_PickerIntialHelperText%>"
                VisibleSuggestions="3"
                Rows="1"
                AllowMultipleEntities="false"
                CssClass="ms-long ms-spellcheck-true" />

Also, how to modify it to enable multi-selection?

Answer 1

For multiple selection Set AllowMultipleEntities="true" and for group set PrincipalAccountType = "SPGroup".

<SharePoint:ClientPeoplePicker
            Required="true"
            ValidationEnabled="true"
            ID="peoplePicker"
            runat="server"
            InitialHelpText="<%$Resources:wss,aclinv_PickerIntialHelperText%>"
            VisibleSuggestions="3"
            Rows="1"
            AllowMultipleEntities="true"
            PrincipalAccountType = "SPGroup"
            CssClass="ms-long ms-spellcheck-true" />