的DropDownList只选择第一值 [英] DropDownList only selects the first value

问题描述

我和我的DropDownList的一个问题。阅读张贴在这里的很多后，我仍然无法使工作，使病人问。

I have a problem with my DropDownList. after reading alot of post here i still cant make it work so ill ask.

这是我的C＃code：

this is my C# code:

protected void Page_Load(object sender, EventArgs e)
{
    using (SqlConnection connection = new SqlConnection("Data Source=PCM13812;Initial Catalog=Newsletter;Integrated Security=True"))
    {
        connection.Open();
        SqlCommand cmd = new SqlCommand();
        cmd = new SqlCommand("Select Email From Newsletter", connection);
        EmailList.DataSource = cmd.ExecuteReader();
        EmailList.DataTextField = "Email";
        EmailList.DataBind();
    }
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{

}
protected void Vælg_Click(object sender, EventArgs e)
{
    EmailListe  .Text = EmailList.Text;
}

下面是我的ASP code：

Here is a my Asp code:

<asp:DropDownList ID="EmailList" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"></asp:DropDownList>
    <asp:Button runat="server" ID="Vælg" Text="Vælg Email" OnClick="Vælg_Click" />
    <asp:TextBox runat="server" ID="EmailListe" TextMode="MultiLine" />
    <asp:TextBox ID="Besked" runat="server" />

正如你可以看到我从我的SqlDatabase DropDownList的值。当我选择在DropDownList电子邮件并点击按钮，然后它总是第一个值添加到文本框，即使我选择另一个电子邮件。

As you can see I get the DropDownList value from my SqlDatabase. When I select an Email in the dropdownlist and click the button then it ALWAYS add the first Value to the textbox, even if I select another Email.

我在做什么错了？

推荐答案

只记得ASP.NET是如何工作的，的Page_Load 之前名为您每个服务器往返的事件处理程序列表，然后刷新为默认值。只是检查它不是一个回送：

Just remember how ASP.NET works, Page_Load is called before your event handler for each server roundtrip then list is refreshed to default value. Just check it's not a postback:

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
        return;

    // Your code here
}

编辑：一个小小的建议;你不处理的SqlCommand 和 SQLReader的，你应该提取值，并尽快处理掉以释放资源。这样，他们会被GC回收，这可能是一个大问题，特别是如果你的网站有繁忙的交通......

a small suggestion; you're not disposing SqlCommand and SqlReader, you should extract values and dispose them as soon as possible to free resources. This way they'll be collected by GC and this may be a big problem, especially if your site has heavy traffic...

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