3rdpartylibs/fastreports.wpf/FastReport.Core.Web/Application/Dialog/WebComboBox.cs

using FastReport.Dialog;
using System.Text;
using static FastReport.Web.Constants;

namespace FastReport.Web
{
    public partial class Dialog
    {
        private void ComboBoxChange(ComboBoxControl cb, int index)
        {
            cb.SelectedIndex = index;
            ControlFilterRefresh(cb);
            cb.OnSelectedIndexChanged(null);
        }

        private string GetComboBoxHtml(ComboBoxControl control)
        {
            if (control.Items.Count == 0)
            {
                control.FillData();
                ControlFilterRefresh(control);
            }
            else
            {
                if (control.SelectedIndex == -1)
                    control.SelectedIndex = 0;
                control.SelectedItem = control.Items[control.SelectedIndex];
                control.Text = control.SelectedItem.ToString();
            }

            string id = GetControlID(control);
            string html = $"<select style=\"{GetComboBoxStyle(control)}\" name=\"{control.Name}\"" +
                $" onchange=\"{GetEvent(ONCHANGE, control, SILENT_RELOAD, $"document.getElementById('{id}').selectedIndex")}\"" +
                $" id=\"{id}\" {(control.Enabled ? "" : "disabled")}>{GetComboBoxItems(control)}</select>";
            control.FilterData();
            return html;
        }

        private string GetComboBoxItems(ComboBoxControl control)
        {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < control.Items.Count; i++)
            {
                sb.AppendFormat("<option {0} value=\"{1}\">{2}</option>",
                    i == control.SelectedIndex ? "selected" : "",
                    control.Items[i],
                    control.Items[i]);
            }
            return sb.ToString();
        }

        private string GetComboBoxStyle(ComboBoxControl control)
        {
            return GetStandardStyle(control);
        }        

    }
}