使用ascx目的就是为了提高某部分功能的重复利用，我简单通过源代码说一下对它的参数的输入和数出。

我们以省市区三级连动为例子。

vs2005下ascx页面的代码：

<table width="100%" border="0" cellpadding="0" cellspacing="0">
      <tr>
          <td>
            <asp:DropDownList id="ddlProvince" runat="server" Width="100px" AutoPostBack="True" OnSelectedIndexChanged="ddlProvince_SelectedIndexChanged">   
            </asp:DropDownList>
            <asp:UpdatePanel ID="UpdatePanel1" runat="server" RenderMode="Inline">
                  <ContentTemplate>
                    <asp:DropDownList id="ddlCity" runat="server" Width="100px" AutoPostBack="True" OnSelectedIndexChanged="ddlCity_SelectedIndexChanged">          
                    </asp:DropDownList>
                  </ContentTemplate>
                <Triggers>
                    <asp:AsyncPostBackTrigger ControlID="ddlProvince" EventName="SelectedIndexChanged" />
                </Triggers>
              </asp:UpdatePanel>
              <asp:UpdatePanel ID="UpdatePanel2" runat="server" RenderMode="Inline">
                  <ContentTemplate>
                    <asp:DropDownList id="ddlDistrict" runat="server" Width="100px">            
                     </asp:DropDownList>
                  </ContentTemplate>
                  <Triggers>
                      <asp:AsyncPostBackTrigger ControlID="ddlCity" EventName="SelectedIndexChanged" />
                  </Triggers>
              </asp:UpdatePanel>
          </td>
      </tr>
  </table>

ascx后台代码：

public partial class UserControl_ProvinceAndCityAndDistrict : System.Web.UI.UserControl
{
    ///// <summary>
    ///// 选择区域的iD
    ///// </summary>
    protected  string _districtValue;
    [Bindable(true), Category("Appearance"), DefaultValue("")]
    public string districtValue
    {
        get { return _districtValue; }
        set { _districtValue = value; }
    }

    protected  string _cityValue;
    [Bindable(true), Category("Appearance"), DefaultValue("")]
    public string cityValue
    {
        get { return _cityValue; }
        set { _cityValue = value; }
    }

    protected  string _provinceValue;
    [Bindable(true), Category("Appearance"), DefaultValue("")]
    public string provinceValue
    {
        get { return _provinceValue; }
        set { _provinceValue = value; }
    }

    private void setValue()
    {
        if (_provinceValue != string.Empty)
        {
            this.ddlProvince.SelectedItem.Text = _provinceValue;
        }
        if (_cityValue != string.Empty)
        {
            this.ddlCity.SelectedItem.Text = _cityValue;
        }
        if (_districtValue != string.Empty)
        {
            this.ddlDistrict.SelectedItem.Text = _districtValue;
        }
    }
    public string getValue()
    {
        return this.ddlProvince.SelectedItem.Text + "," + ddlCity.SelectedItem.Text + "," + ddlDistrict.SelectedItem.Text;
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            setProvince();
            this.ddlProvince.SelectedIndex = 0;
            setCity(Convert.ToInt32(this.ddlProvince.SelectedValue));
            this.ddlCity.SelectedIndex = 0;
            setDistrict(Convert.ToInt32(this.ddlCity.SelectedValue));
            setValue();
        }
    }
    private void setProvince()
    {
        CallCenter.BLL.sys_Province province = new CallCenter.BLL.sys_Province();
        DataSet ds = province.getProvinceList();
        this.ddlProvince.DataSource = ds.Tables[0];
        this.ddlProvince.DataValueField = "provinceid";
        this.ddlProvince.DataTextField = "provincename";
        this.ddlProvince.DataBind();
    }
    private void setCity(int provinceId)
    {
        CallCenter.BLL.sys_City city = new CallCenter.BLL.sys_City();
        DataSet ds = city.getCityList(provinceId);
        this.ddlCity.DataSource = ds.Tables[0];
        this.ddlCity.DataValueField = "cityid";
        this.ddlCity.DataTextField = "cityName";
        this.ddlCity.DataBind();
    }
    private void setDistrict(int cityId)
    {
        CallCenter.BLL.sys_District district = new CallCenter.BLL.sys_District();
        DataSet ds = district.getDistrictList(cityId);
        this.ddlDistrict.DataSource = ds.Tables[0];
        this.ddlDistrict.DataValueField = "districtid";
        this.ddlDistrict.DataTextField = "districtname";
        this.ddlDistrict.DataBind();
    }
    protected void ddlProvince_SelectedIndexChanged(object sender, EventArgs e)
    {
        setCity(Convert.ToInt32(this.ddlProvince.SelectedValue));
        this.ddlCity.SelectedIndex = 0;
        setDistrict(Convert.ToInt32(this.ddlCity.SelectedValue));
    }
    protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
    {
        setDistrict(Convert.ToInt32(this.ddlCity.SelectedValue));
    }
}

使用aspx页面的后台调用部分代码：

如何传入参数，对于ascx的参数一般通过自定义页面属性来实现的。在ascx的页面我定义了几个属性

provincevalue，cityvalue，districtvalue，把你所需要传入的参数通过下面的方式给它就可以了，至于出入后你需要怎么处理你就自己操作了，上面有我的简单处理方式。

  string[] strAddress=ds.Tables[0].Rows[i]["value"].ToString().Split(',');
  this.ProvinceAndCityAndDistrict1.provinceValue = strAddress[0];
  this.ProvinceAndCityAndDistrict1.cityValue = strAddress[1];
  this.ProvinceAndCityAndDistrict1.districtValue = strAddress[2];

从ascx获取输出的东西的话，我目前采用的是通过公共函数调用来实现的

比如在对aspx页面的信息进行保存的时候，我要获取到当前所选择的省市区信息，我是通过方法getValue()来获取返回的字符窜的，你可以根据自己的需要来定义适当的方法。

this.ProvinceAndCityAndDistrict1.getValue();

希望我通过简单的举例说明能够帮助大家对ascx的使用有个初步简单的了解。有好的方法相互交流，共同进步！