Question

我正在根据项目列表执行销售订单。我有两个下拉列表。 First下拉列表从Projects表中检索数据。第二个下拉列表是根据第一个下拉列表中的选定值填充数据。

下面显示了项目和任务的下拉列表的源代码。

    <!--Project-->
    <div class="form-group">
        <label class="control-label col-lg-4">
            Project</label>
        <div class="col-lg-8">
            <asp:DropDownList ID="ddlProjects" runat="server" class="form-control" 
                AutoPostBack="True" DataTextField="Select a project..." DataValueField="AutoId" 
                onselectedindexchanged="ddlProjects_SelectedIndexChanged" />
        </div>
    </div>

    <!--Tasks-->
    <div class="form-group">
        <label class="control-label col-lg-4">
            Task</label>
        <div class="col-lg-8">
            <asp:DropDownList ID="ddlTasks" runat="server" class="form-control" />
        </div>
    </div>

下面显示了下拉列表背后的代码

void GetProjects()
{
    con.Open();
    SqlCommand cmd = new SqlCommand();
    cmd.Connection = con;
    cmd.CommandText = "SELECT ProjectID, Name FROM Projects WHERE Status = 'On Going'";
    SqlDataReader dr = cmd.ExecuteReader();
    ddlProjects.DataSource = dr;
    ddlProjects.DataTextField = "Name";
    ddlProjects.DataValueField = "ProjectID";
    ddlProjects.DataBind();
    con.Close();
}

protected void ddlProjects_SelectedIndexChanged(object sender, EventArgs e)
{
    DataTable table = new DataTable();

    var ID = int.Parse(ddlProjects.SelectedValue);

    string sql = "SELECT TaskID, Name FROM ProjectTasks WHERE ProjectID = @ProjectID";
    SqlCommand cmd = new SqlCommand(sql, con);
    cmd.Connection = con;
    SqlDataAdapter ad = new SqlDataAdapter(cmd);
    cmd.Parameters.AddWithValue("@ProjectID", ID);
    ad.Fill(table);
    ddlTasks.DataTextField = "Name";
    ddlTasks.DataSource = table;
    ddlTasks.DataBind();
}

问题在于每次我打开销售订单表时，默认的DataTextValue都不是我在源代码中声明的那个＆＃34;选择一个项目＆＃34;但它显示了第一条记录。

另一件事是我觉得代码仍有问题我无法识别它是什么。

如果您有任何澄清，请告诉我。

Answer 1

您需要从aspx中删除DataTextField="Select a project..." DataValueField="AutoId"。您在代码中定义了这一点。

添加您的第一个选项并设置AppendDataBoundItems = true

ddlProjects.Items.Add(new ListItem("Select a project...",""));
ddlProjects.AppendDataBoundItems = true;
ddlProjects.DataSource = dr;
ddlProjects.DataTextField = "Name";
ddlProjects.DataValueField = "ProjectID";
ddlProjects.DataBind();

确保未选择空白项目

protected void ddlProjects_SelectedIndexChanged(object sender, EventArgs e)
{
    ddlTasks.Items.Clear();
    int ID = 0;
    if (int.TryParse(ddlProjects.SelectedValue, out ID))
    {
        DataTable table = new DataTable();
        string sql = "SELECT TaskID, Name FROM ProjectTasks WHERE ProjectID = @ProjectID";
        SqlCommand cmd = new SqlCommand(sql, con);
        cmd.Connection = con;
        SqlDataAdapter ad = new SqlDataAdapter(cmd);
        cmd.Parameters.AddWithValue("@ProjectID", ID);
        ad.Fill(table);
        ddlTasks.DataTextField = "Name";
        ddlTasks.DataSource = table;
        ddlTasks.DataBind();
    }
}

如何基于另一个DropDownList填充DropDownList

1 个答案: