C# 具有SelectedIndex=0的DropDownList
我编写了一个简单的程序,它与数据库连接,从两个表中读取数据,并将它们写入两个DropDownLists(DDL)。DDL具有类似父级和子级的结构。这是我的代码:C# 具有SelectedIndex=0的DropDownList,c#,asp.net,sql,drop-down-menu,C#,Asp.net,Sql,Drop Down Menu,我编写了一个简单的程序,它与数据库连接,从两个表中读取数据,并将它们写入两个DropDownLists(DDL)。DDL具有类似父级和子级的结构。这是我的代码: protected void Page_Load(object sender, EventArgs e) { FillControls(); if (!IsPostBack) { ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindCon
protected void Page_Load(object sender, EventArgs e)
{
FillControls();
if (!IsPostBack)
{
ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindControl("ddlTurCountry"), null);
}
else
{
if (((DropDownList)PlaceHolder1.FindControl("ddlTurCountry")).SelectedIndex == 0) ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindControl("ddlTurCountry"), null); //without this string dropDownList doesn't call ddl_SelectedIndexChanged() when it's SelectedIndex=0
}
}
private void FillControls()
{
Panel panel = new Panel();
Label lbl = new Label();
lbl.Text = "Country: ";
panel.Controls.Add(lbl);
DropDownList ddl = new DropDownList();
ddl.ID = "ddlTurCountry";
ddl.DataTextField = "CountryName";
ddl.DataValueField = "CountryName";
ddl.SelectedIndexChanged += new EventHandler(ddl_SelectedIndexChanged);
ddl.AutoPostBack = true;
panel.Controls.Add(ddl);
panel.Controls.Add(new LiteralControl("<br />"));
lbl = new Label();
lbl.Text = "Kurort: ";
panel.Controls.Add(lbl);
ddl = new DropDownList();
ddl.ID = "ddlTurKurort";
ddl.DataTextField = "KurortName";
ddl.DataValueField = "KurortName";
panel.Controls.Add(ddl);
PlaceHolder1.Controls.Add(panel);
FillDDL("ddlTurCountry", "SELECT CountryName from Countries");
}
private void ddl_SelectedIndexChanged(object sender, EventArgs e)
{
if (((DropDownList)sender).ID == "ddlTurCountry")
{
FillDDL("ddlTurKurort", "SELECT Kurorts.KurortName FROM Kurorts INNER JOIN Countries ON Countries.idCountry = Kurorts.idCountry WHERE (Countries.CountryName = N'" + ((DropDownList)PlaceHolder1.FindControl("ddlTurCountry")).SelectedValue + "')");
}
}
private void FillDDL(string ddlID, string SQLCommand)
{
((DropDownList)PlaceHolder1.FindControl(ddlID)).DataSource = GetDataFromDB(SQLCommand);
((DropDownList)PlaceHolder1.FindControl(ddlID)).DataBind();
}
private DataTable GetDataFromDB(string SQLCommand)
{
DataTable dt = new DataTable();
string sqlcnString = @"Data Source=.\SQLEXPRESS;Initial Catalog=turs;Integrated Security=True;Pooling=False";
SqlConnection sqlcn = new SqlConnection(sqlcnString);
if (sqlcn.State.ToString() == "Closed") sqlcn.Open();
SqlDataAdapter dataAdapter = new SqlDataAdapter(SQLCommand, sqlcn);
dataAdapter.Fill(dt);
sqlcn.Close();
return dt;
}
加载到页面,但我不喜欢这样,我不明白为什么当选择dex=0
时它不起作用。
已解决
每次页面刷新时,您都会填充下拉列表。不要那样做。
仅在以下情况下调用FillControls()!第页,回发
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
FillControls();
//Not sure why you have this here, probably not needed
ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindControl("ddlTurCountry"), null);
}
else
{
}
}
回发后,所有内容都会消失,因为oll控件会创建动态dropdownlist为什么需要动态创建?您不能将其放在您的aspx页面上吗?您还可以查看以下内容:
protected void Page_Init(object sender, EventArgs e)
{
FillControls();
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack) ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindControl("ddlTurCountry"), null);
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
FillControls();
//Not sure why you have this here, probably not needed
ddl_SelectedIndexChanged((DropDownList)PlaceHolder1.FindControl("ddlTurCountry"), null);
}
else
{
}
}