在第二个下拉列表中填充“选择”下拉列表

本文关键字：下拉列表 选择 第二个 填充 | 更新日期: 2023-09-27 18:31:29

所以我正在尝试从另一个下拉列表中填充一个下拉列表。 我已经测试了我正在使用的存储过程，并且在输入值时，我得到了正确的结果。 我知道有很多这样的问题，但似乎没有一个能解决我的问题。

protected void Page_Load(object sender, EventArgs e)
{
    DataTable environments = new DataTable();
    var connection = ConfigurationManager.ConnectionStrings["Connection"].ConnectionString;
    using (SqlConnection conn = new SqlConnection(connection))
    {
        SqlDataAdapter adapter = new SqlDataAdapter("SELECT Environment FROM Environments", conn);
        adapter.Fill(environments);
        ddlEnvironment.Items.Insert(0, new ListItem(String.Empty, String.Empty));
        ddlEnvironment.SelectedIndex = 0;
        ddlEnvironment.DataSource = environments;
        ddlEnvironment.DataTextField = "Environment";
        ddlEnvironment.DataValueField = "Environment";
        ddlEnvironment.DataBind();
        SqlCommand cmd = new SqlCommand();
        SqlDataAdapter adapter2 = new SqlDataAdapter();
        DataTable servers = new DataTable();
        cmd = new SqlCommand("sp_EnvironmentSelection", conn);
        cmd.Parameters.AddWithValue("@Environment", ddlEnvironment.SelectedValue);
        cmd.CommandType = System.Data.CommandType.StoredProcedure;
        adapter2.SelectCommand = cmd;
        adapter2.Fill(servers);
        ddlServer.Items.Insert(0, new ListItem(String.Empty, String.Empty));
        ddlServer.SelectedIndex = 0;
        ddlServer.DataSource = servers;
        ddlServer.DataTextField = "ServerName";
        ddlServer.DataValueField = "ServerIP";
        ddlServer.DataBind();
    }
}

问题是，无论我在第一个下拉菜单上的选择如何，我都没有在第二个下拉菜单上获得任何选择。

如果需要，这是存储的过程。

@Environment    nvarchar(50)
AS
BEGIN
SET NOCOUNT ON
SELECT Server.ServerName, Server.ServerIP, Environments.Environment
FROM Server
INNER JOIN Environments
ON
Environments.Environment=Server.Environment
WHERE Server.Environment=@Environment
END

在第二个下拉列表中填充“选择”下拉列表

如果在执行代码时单步执行代码，您将看到调用cmd.Parameters.AddWithValue("@Environment", ddlEnvironment.SelectedValue);时，ddlEnvironment.SelectedValue 将不会设置为任何内容。这是因为在运行此代码时，它正好在 ddlEnvironment 绑定到其数据之后。它当时没有关于用户选择的内容的信息。

您需要将第二个列表的绑定移动到处理 ddlEvironment.SelectedIndexChanged 事件的事件处理程序中。在那里，ddlEnvironment.SelectedValue将被设置为用户选择的内容。而在Page_Load中，您不希望每次有回发时都重新绑定第一个列表，因此需要将其包装在if (!Page.IsPostBack)中。

请参阅此处的问题：DropDownList 的 SelectedIndexChanged 事件未触发

asp 代码中的第一个下拉列表需要如下所示：

<asp:DropDownList ID="ddlEnvironemnt" runat="server" AutoPostBack="True" 
        onselectedindexchanged="ddlEnvironemnt_SelectedIndexChanged">
    </asp:DropDownList>

您的page_load如下所示：

protected void Page_Load(object sender, EventArgs e)
{
    if (Page.IsPostBack)
    {
        return;
    }
    DataTable environments = new DataTable();
    var connection = ConfigurationManager.ConnectionStrings["Connection"].ConnectionString;
    using (SqlConnection conn = new SqlConnection(connection))
    {
        SqlDataAdapter adapter = new SqlDataAdapter("SELECT Environment FROM Environments", conn);
        adapter.Fill(environments);
        ddlEnvironment.Items.Insert(0, new ListItem(String.Empty, String.Empty));
        ddlEnvironment.SelectedIndex = 0;
        ddlEnvironment.DataSource = environments;
        ddlEnvironment.DataTextField = "Environment";
        ddlEnvironment.DataValueField = "Environment";
        ddlEnvironment.DataBind();
    }
}

您将有一个事件处理程序：

protected void ddlEnvironemnt_SelectedIndexChanged(object sender, EventArgs e)
{
    var connection = ConfigurationManager.ConnectionStrings["Connection"].ConnectionString;
    using (SqlConnection conn = new SqlConnection(connection))
    {
        SqlCommand cmd = new SqlCommand();
        SqlDataAdapter adapter2 = new SqlDataAdapter();
        DataTable servers = new DataTable();
        cmd = new SqlCommand("sp_EnvironmentSelection", conn);
        cmd.Parameters.AddWithValue("@Environment", ddlEnvironment.SelectedValue);
        cmd.CommandType = System.Data.CommandType.StoredProcedure;
        adapter2.SelectCommand = cmd;
        adapter2.Fill(servers);
        ddlServer.Items.Insert(0, new ListItem(String.Empty, String.Empty));
        ddlServer.SelectedIndex = 0;
        ddlServer.DataSource = servers;
        ddlServer.DataTextField = "ServerName";
        ddlServer.DataValueField = "ServerIP";
        ddlServer.DataBind();
    }
}
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