// 使用原生JavaScript
function populateDropdown() {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', '/api/GetDropdownData', true);
    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4 && xhr.status === 200) {
            var data = JSON.parse(xhr.responseText);
            var dropdown = document.getElementById('myDropdown');
            dropdown.innerHTML = ''; // 清空现有选项
            
            // 添加默认选项
            var defaultOption = document.createElement('option');
            defaultOption.text = '--请选择--';
            defaultOption.value = '';
            dropdown.add(defaultOption);
            
            // 添加数据选项
            data.forEach(function(item) {
                var option = document.createElement('option');
                option.text = item.text;
                option.value = item.value;
                dropdown.add(option);
            });
        }
    };
    xhr.send();
}

// 使用jQuery
$(document).ready(function() {
    $.ajax({
        url: '/api/GetDropdownData',
        type: 'GET',
        dataType: 'json',
        success: function(data) {
            var dropdown = $('#myDropdown');
            dropdown.empty();
            dropdown.append($('<option>').text('--请选择--').val(''));
            
            $.each(data, function(index, item) {
                dropdown.append($('<option>').text(item.text).val(item.value));
            });
        },
        error: function(xhr, status, error) {
            console.error('Error loading dropdown data:', error);
        }
    });
});

[System.Web.Services.WebMethod]
public static List<DropdownItem> GetDropdownData()
{
    List<DropdownItem> items = new List<DropdownItem>();
    
    // 从数据库或其他数据源获取数据
    // 示例数据
    items.Add(new DropdownItem { Value = "1", Text = "选项1" });
    items.Add(new DropdownItem { Value = "2", Text = "选项2" });
    items.Add(new DropdownItem { Value = "3", Text = "选项3" });
    
    return items;
}

public class DropdownItem
{
    public string Value { get; set; }
    public string Text { get; set; }
}

[ApiController]
[Route("api/[controller]")]
public class DropdownController : ControllerBase
{
    [HttpGet("GetDropdownData")]
    public IActionResult GetDropdownData()
    {
        var items = new List<DropdownItem>
        {
            new DropdownItem { Value = "1", Text = "选项1" },
            new DropdownItem { Value = "2", Text = "选项2" },
            new DropdownItem { Value = "3", Text = "选项3" }
        };
        
        return Ok(items);
    }
}