从数据库填充DropDownList的正确方法是什么?
我正在从SQL Server数据库填充DropDownList,如下所示。它工作正常,但我不确定这是一个好方法。有人可以阐明这种方法并进行一些改进吗?
private void LoadSubjects(){
ddlSubjects.Items.Clear();
string selectSQL = "SELECT SubjectID,SubjectName FROM Students.dbo.Subjects";
SqlConnection con = new SqlConnection(connectionString);
SqlCommand cmd = new SqlCommand(selectSQL, con);
SqlDataReader reader;
try
{
ListItem newItem = new ListItem();
newItem.Text = "<Select Subject>";
newItem.Value = "0";
ddlSubjects.Items.Add(newItem);
con.Open();
reader = cmd.ExecuteReader();
while (reader.Read())
{
newItem = new ListItem();
newItem.Text = reader["SubjectName"].ToString();
newItem.Value = reader["SubjectID"].ToString();
ddlSubjects.Items.Add(newItem);
}
reader.Close();
}
catch (Exception err)
{
//TODO
}
finally
{
con.Close();
}
}
回答:
您可以将DropDownList绑定到数据源(DataTable,List,DataSet,SqlDataSource等)。
例如,如果您想使用数据表:
ddlSubject.DataSource = subjectsTable;ddlSubject.DataTextField = "SubjectNamne";
ddlSubject.DataValueField = "SubjectID";
ddlSubject.DataBind();
private void LoadSubjects(){
DataTable subjects = new DataTable();
using (SqlConnection con = new SqlConnection(connectionString))
{
try
{
SqlDataAdapter adapter = new SqlDataAdapter("SELECT SubjectID, SubjectName FROM Students.dbo.Subjects", con);
adapter.Fill(subjects);
ddlSubject.DataSource = subjects;
ddlSubject.DataTextField = "SubjectNamne";
ddlSubject.DataValueField = "SubjectID";
ddlSubject.DataBind();
}
catch (Exception ex)
{
// Handle the error
}
}
// Add the initial item - you can add this even if the options from the
// db were not successfully loaded
ddlSubject.Items.Insert(0, new ListItem("<Select Subject>", "0"));
}
要通过标记而不是代码隐藏设置初始值,请指定选项并将AppendDataBoundItems属性设置为true:
<asp:DropDownList ID="ddlSubject" runat="server" AppendDataBoundItems="true"> <asp:ListItem Text="<Select Subject>" Value="0" />
</asp:DropDownList>
然后,您可以将DropDownList绑定到背后代码中的数据源(只记得删除:
ddlSubject.Items.Insert(0, new ListItem("<Select Subject>", "0"));
从后面的代码中,否则您将有两个“”项。
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