在Ajax级联DropDown中加载数据库值

Question

这是我第一次使用Ajax，这也是我的第一个C＃.NET项目，所以我很新。我使用的是.NET 4.0。

我已经成功实现了Ajax级联下拉列表，并在提交后，数据存储在数据库中。但是，此页面还具有“编辑”功能，这意味着如果数据库中已填充所述下拉列表的值，则应“显示”，并允许用户更改它。这是我被卡住的地方。如果db中已存在这些下拉列表的值，我该如何显示？

我对其他非Ajax字段有一个try / catch，我已经尝试过这些，但无济于事。我也会列出那个。

代码背后：

 public partial class Research : System.Web.UI.Page
{

    //Page Load
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {

/Create data table to populate fields with values from the selected record. 
            DataTable dt = new DataTable();
            dt = selectDetails();

            //Call Try/Catch Blocks to load fields.
            tryRootCauseCategoryDD(cboRootCauseCategory, dt.Rows[0]["rootCauseCategory"].ToString());
            tryRootCauseDD(cboRootCause, dt.Rows[0]["rootCause"].ToString());
        } 
    }
protected void tryRootCauseCategoryDD(DropDownList cboRootCauseCategory, string ddSelected)
    {

        try
        {
            cboRootCauseCategory.SelectedValue = ddSelected;
        }
        catch
        {
            cboRootCauseCategory.SelectedIndex = 0;
        }
    }

    protected void tryRootCauseDD(DropDownList cboRootCause, string ddSelected)
    {
        try
        {
            cboRootCause.SelectedValue = ddSelected;
        }
        catch
        {
            cboRootCause.SelectedIndex = 0;
        }
    }

protected DataTable selectDetails()
    {
        DataTable dt = new DataTable();
        dt = dataAccess.ExecuteDataTable
            (
                "spRecordDetails", dataAccess.DEV, new SqlParameter[1]
                {
                    new SqlParameter ("@vRecID", Request.QueryString["recID"].ToString()) 
                }

            );

        return dt;
    }

ASPX：

<asp:DropDownList ID="cboRootCauseCategory" runat="server"></asp:DropDownList>
        <ajaxToolkit:CascadingDropDown ID="ccdRootCauseCategory" runat="server" Category="RootCauseCategory"
        TargetControlID="cboRootCauseCategory" PromptText="(Please select:)" LoadingText="Loading.." 
        ServiceMethod="BindRootCauseCategoryDetails" ServicePath="CascadingDropDown.asmx">
        </ajaxToolkit:CascadingDropDown>
<asp:DropDownList ID="cboRootCause" runat="server"></asp:DropDownList>
        <ajaxToolkit:CascadingDropDown ID="ccdRootCause" runat="server" Category="RootCause" ParentControlID="cboRootCauseCategory" 
        TargetControlID="cboRootCause" PromptText="(Please select:)" LoadingText="Loading.." 
        ServiceMethod="BindRootCauseDetails" ServicePath="CascadingDropDown.asmx">
        </ajaxToolkit:CascadingDropDown>

网络服务：

[WebService(Namespace = "http://microsoft.com/webservices/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

//To allow this Web Service to be called from script, using ASP.NET AJAX. 

[System.Web.Script.Services.ScriptService()]
public class CascadingDropDown : System.Web.Services.WebService

{
    //Database connection string
    //private static string strconnection = ConfigurationManager.AppSettings["DEV"].ToString();
    private static string strconnection = System.Configuration.ConfigurationManager.ConnectionStrings["DEV"].ConnectionString;

    //database connection
    SqlConnection conCategory = new SqlConnection(strconnection);
    public CascadingDropDown()
    {
        //Uncomment the following line if using designed components
        //InitializeComponent();
    }

    /// WebMethod to Populate Root Cause Category Dropdown
    [WebMethod]
    public CascadingDropDownNameValue[] BindRootCauseCategoryDetails(string knownCategoryValues, string category)
    {
        conCategory.Open();
        SqlCommand cmdRootCauseCategory = new SqlCommand
        ("Select Distinct RootCauseCategory From RootCause", conCategory);

        cmdRootCauseCategory.ExecuteNonQuery();
        SqlDataAdapter daRootCauseCategory = new SqlDataAdapter(cmdRootCauseCategory);
        DataSet dsRootCauseCategory = new DataSet();
        daRootCauseCategory.Fill(dsRootCauseCategory);
        conCategory.Close();


        //create list and add items in it by looping through dataset table
        List<CascadingDropDownNameValue> RootCauseCategoryDetails = new List<CascadingDropDownNameValue>();
        foreach (DataRow dtrow in dsRootCauseCategory.Tables[0].Rows)
        {
            //string recID = dtrow["recID"].ToString();
            string RootCauseCategory = dtrow["RootCauseCategory"].ToString();
            string RootCauseCategoryValue = dtrow["RootCauseCategory"].ToString();
            RootCauseCategoryDetails.Add(new CascadingDropDownNameValue(RootCauseCategory,RootCauseCategoryValue));
        }
        return RootCauseCategoryDetails.ToArray();  
    }

    /// WebMethod to Populate Root Cause Dropdown
    [WebMethod]
    public CascadingDropDownNameValue[] BindRootCauseDetails(string knownCategoryValues, string category)
    {
        string rootCauseCategory;

        //This method will return a StringDictionary containing the name/value pairs of the currently selected values
        StringDictionary rootCauseCategoryDetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);

        rootCauseCategory = (rootCauseCategoryDetails["RootCauseCategory"]);
        conCategory.Open();
        SqlCommand cmdRootCause = new SqlCommand("select recID, rootCause from RootCause where rootCauseCategory= @vRootCauseCategory", conCategory);
        cmdRootCause.Parameters.AddWithValue("@vRootCauseCategory", rootCauseCategory);
        cmdRootCause.ExecuteNonQuery();

        SqlDataAdapter daRootCause = new SqlDataAdapter(cmdRootCause);
        DataSet dsRootCause = new DataSet();
        daRootCause.Fill(dsRootCause);
        conCategory.Close();

        //create list and add items in it by looping through dataset table
        List<CascadingDropDownNameValue> rootCauseDetails = new List<CascadingDropDownNameValue>();
        foreach (DataRow dtrow in dsRootCause.Tables[0].Rows)
        {
            string recID = dtrow["recID"].ToString();
            string rootCause = dtrow["rootCause"].ToString();
            rootCauseDetails.Add(new CascadingDropDownNameValue(rootCause, recID));
        }
        return rootCauseDetails.ToArray();
    }
}

Answer 1

我决定废弃网络服务的想法，而是选择了更新面板。可能没有多余的方法可以做到这一点，但它正在发挥作用。

最终解决方案：

标记页：

<asp:TableCell Width="500">
    <asp:UpdatePanel ID="UpdatePanel" runat="server">
        <ContentTemplate>
        <p><asp:DropDownList ID="cboRootCauseCategory" runat="server" AutoPostBack="True" onselectedindexchanged="cboRootCauseCategory_SelectedIndexChanged"></asp:DropDownList>&nbsp;
        <asp:DropDownList ID="cboRootCause" runat="server" AutoPostBack="true"></asp:DropDownList></p>
        </ContentTemplate>
</asp:UpdatePanel>
    </asp:TableCell>

代码背后：

if (!IsPostBack)
        {
            //Create data table to populate fields with values from the selected record. 
            DataTable dt = new DataTable();
            dt = selectDetails();

            //Call Try/Catch Blocks to load fields.
            tryRootCauseCategoryDD(cboRootCauseCategory, dt.Rows[0]["rootCauseCategory"].ToString());
            tryRootCauseDD(cboRootCause, dt.Rows[0]["rootCause"].ToString());

        } 

 protected void tryRootCauseCategoryDD(DropDownList cboRootCauseCategory, string ddSelected)
    {
        try
        {
            //Load Root Cause Category Drop Down
            DataTable RootCauseCategories = new DataTable();
            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DEV"].ConnectionString))
            {
                SqlDataAdapter adapter = new SqlDataAdapter("Select recID, rootCauseCategory From RootCauseCategory", con);
                adapter.Fill(RootCauseCategories);
                cboRootCauseCategory.DataSource = RootCauseCategories;
                cboRootCauseCategory.DataTextField = "RootCauseCategory";
                cboRootCauseCategory.DataValueField = "recID";
                cboRootCauseCategory.DataBind();
            }
            cboRootCauseCategory.Items.Insert(0, new ListItem("(Please select:)", "0"));
            cboRootCauseCategory.SelectedValue = ddSelected;
        }
        catch
        {
            //Load Root Cause Category Drop Down
            DataTable RootCauseCategories = new DataTable();
            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DEV"].ConnectionString))
            {
                SqlDataAdapter adapter = new SqlDataAdapter("Select recID, rootCauseCategory From RootCauseCategory", con);
                adapter.Fill(RootCauseCategories);
                cboRootCauseCategory.DataSource = RootCauseCategories;
                cboRootCauseCategory.DataTextField = "RootCauseCategory";
                cboRootCauseCategory.DataValueField = "recID";
                cboRootCauseCategory.DataBind();
            }
            cboRootCauseCategory.Items.Insert(0, new ListItem("(Please select:)", "0"));
            cboRootCauseCategory.SelectedIndex = 0;
        }
    }

    protected void tryRootCauseDD(DropDownList cboRootCause, string ddSelected)
    {

        try
        {
            string cboRootCauseCategoryID = Convert.ToString(cboRootCauseCategory.SelectedValue);
            DataTable RootCauses = new DataTable();
            using (SqlConnection con2 = new SqlConnection(ConfigurationManager.ConnectionStrings["DEV"].ConnectionString))
            {
                SqlDataAdapter adapter = new SqlDataAdapter("Select recID, rootCause, rootCauseCategory From RootCause Where rootCauseCategory = '" + cboRootCauseCategoryID + "'", con2);

                adapter.Fill(RootCauses);
                cboRootCause.DataSource = RootCauses;
                cboRootCause.DataTextField = "RootCause";
                cboRootCause.DataValueField = "recID";
                cboRootCause.DataBind();
            }
            cboRootCause.SelectedValue = ddSelected;
        }
        catch
        {
            cboRootCause.SelectedIndex = 0;
        }
    }

    protected void cboRootCauseCategory_SelectedIndexChanged(object sender, EventArgs e)
    {
        string cboRootCauseCategoryID = Convert.ToString(cboRootCauseCategory.SelectedValue);

        DataTable RootCauses = new DataTable();
        using (SqlConnection con2 = new SqlConnection(ConfigurationManager.ConnectionStrings["DEV"].ConnectionString))
        {
            SqlDataAdapter adapter = new SqlDataAdapter("Select recID, rootCause, rootCauseCategory From RootCause Where rootCauseCategory = '" + cboRootCauseCategoryID + "'", con2);

            adapter.Fill(RootCauses);
            cboRootCause.DataSource = RootCauses;
            cboRootCause.DataTextField = "RootCause";
            cboRootCause.DataValueField = "recID";
            cboRootCause.DataBind();
        }
        cboRootCause.Items.Insert(0, new ListItem("(Please select:)", "0"));