This seems to be a common problem. I have tried different solutions but its still not working. This is my code.
HTML:
<div class="form-group">
<label for="exampleInputEmail1">Artist *</label>
<asp:DropDownList ID="artistDropdown" runat="server" CssClass="form-control" AutoPostBack="True" OnSelectedIndexChanged="artistDropdown_SelectedIndexChanged" ViewStateMode="Enabled"></asp:DropDownList>
<asp:TextBox ID="mytest" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="artistDropdown" SetFocusOnError="true" ErrorMessage="Required Field" Font-Bold="True" Font-Names="Arial" Font-Size="X-Small" ForeColor="Red"></asp:RequiredFieldValidator>
<asp:Label ID="lblMessage" runat="server" CssClass="help-block" Visible="False">Cant select Artist with no Manager</asp:Label>
</div>
Function: OnSelectedIndexChanged
protected void artistDropdown_SelectedIndexChanged(object sender, EventArgs e)
{
string selectedArtist = artistDropdown.SelectedValue;
mytest.Text = selectedArtist;
string query = "Select [Manager ID] from Artist Where ID = '" + selectedArtist + "'";
string myConnection = dbController.connectionString;
SqlConnection conn = new SqlConnection(myConnection);
SqlCommand cmd = new SqlCommand(query, conn);
conn.Open();
object obj = cmd.ExecuteScalar();
if (obj is System.DBNull)
{
artistDropdown.SelectedValue = "";
lblMessage.Visible = true;
}
else
{
lblMessage.Visible = false;
}
conn.Close();
}
I am loading DropDownList in Page_Load() function and AutoPostBack="True" is set for DropDownList.
I have also made a TextBox which is being set to the selectedValue from DropDownList to check if on OnSelectedIndexChanged is firing. But text box remains empty.
What am I doing wrong?
Did you put the binding of your dropdown in the if (!postback) {} ?
If you rebind the list after every postback, you get the value of the first list item when you reach the artistDropdown_SelectedIndexChanged event.
If this item has an empty string value...
Related
i have this code:
protected void Button1_Click(object sender, EventArgs e)
{
System.Data.SqlClient.SqlConnection sc = new System.Data.SqlClient.SqlConnection(GetConnectionString());
{
System.Data.SqlClient.SqlCommand cmd;
sc.Open();
cmd = new System.Data.SqlClient.SqlCommand("SET IDENTITY_INSERT Zapas OFF INSERT INTO Zapas (Zapas.Sezona,.....)SELECT Zapas.Sezona,... FROM Zapas WHERE ID_zapas=#ID;", sc);
cmd.Parameters.Add(new System.Data.SqlClient.SqlParameter("#ID", System.Data.SqlDbType.Text)).Value = (TextBox)ListView1.FindControl("box1");
cmd.ExecuteNonQuery();
sc.Close();
Response.Redirect("~/Zapasy_seznam.aspx");
}
}
I need take value ID from listview, but with this code I have this error:
...expects the parameter '#ID', which was not supplied....
This part of my listview...
<asp:ListView ID="ListView1" runat="server" DataKeyNames="ID_zapas" DataSourceID="SqlDataSource1" style="text-align: center ">
<AlternatingItemTemplate>
<tr style="background-color: #e9ffe9;color: #284775;text-align:center">
<td>
<asp:TextBox ID="box1" runat="server" Text='<%# Eval("ID_zapas") %>' Visible="false" />
...
<td style="width:50px;background-color:white">
<asp:LinkButton ID="Button1" runat="server" OnClick="Button1_Click" Visible='<%# HttpContext.Current.User.IsInRole("admin") %>' CausesValidation="False" OnClientClick="javascript: return confirm('Opravdu chcete zápas zkopírovat?');">
<asp:Image ID="Image2" runat="server" ImageUrl="~/Icons/copy.png" Width="29px" Height="29px" ToolTip="Zkopírovat zápas" />
</asp:LinkButton>
</td>
</tr>
</AlternatingItemTemplate>
Have you some idea?
As per comments, please try this:
using System.Data.SqlClient;
protected void Button1_Click(object sender, EventArgs e)
{
var box1 = (TextBox)((LinkButton)sender).Parent.FindControl("box1");
using (var sc = new SqlConnection(GetConnectionString()))
{
using (var cmd = sc.CreateCommand())
{
sc.Open();
cmd.CommandText = "SET IDENTITY_INSERT Zapas OFF INSERT INTO Zapas (Zapas.Sezona,.....)SELECT Zapas.Sezona,... FROM Zapas WHERE ID_zapas=#ID;";
cmd.Parameters.AddWithValue("#ID", box1.Text);
cmd.ExecuteNonQuery();
sc.Close();
Response.Redirect("~/Zapasy_seznam.aspx");
}
}
}
When using data-aware controls such as a ListView here, the controls are created with automatic unique IDs per data item. This means that you can have more than 1 of the same control (such as "box1" in this case) within the page that should be referenced by the data item (((LinkButton)sender).Parent which is ListViewDataItem, representing the row).
ListViewDataItem.FindControl will find controls of a specific server ID within its own child scope, allowing you to get values for controls within the same row of the button that is being clicked.
I have a FormView which allows inserting of records into a table, and then also sends out a confirmation email that a record has been added. The email is supposed to go a particular set of users, based on a department selected. So I have the below. All works well, except after I add a record, and the email sends, and then it takes me back, and when I click the Add new record button again I get 'Could not find control 'formViewNewItem$ddlInsertDepartment' in ControlParameter 'RoleID'.' It's like the formView is staying in insertmode or something after a record is inserted into the table.
Data source for emails to be sent:
<asp:SqlDataSource ID="dsourceToEmails" runat="server"
ConnectionString="<%$ ConnectionStrings:TestConnectionString %>"
SelectCommand="SELECT [Email] + ',' FROM [Users] WHERE [Role] = #RoleID FOR XML PATH ('')">
</asp:SqlDataSource>
FormView code:
<asp:FormView ID="formViewNewItem" runat="server" DataKeyNames="Test_ID"
DataSourceID="testDataSource" OnDataBound="formViewNewItem_DataBound"
OnItemInserted="testRecord_Inserted">
<InsertItemTemplate>
<asp:DropDownList ID="ddlInsertDepartment" runat="server" ClientIDMode="Static">
<asp:ListItem></asp:ListItem>
<asp:ListItem>Accounting</asp:ListItem>
<asp:ListItem>Marketing</asp:ListItem>
<asp:ListItem>Programming</asp:ListItem>
</asp:DropDownList>
</InsertItemTemplate>
<ItemTemplate>
<asp:Button ID="btnAddNewRecord" runat="server" CausesValidation="False"
CommandName="New" Font-Bold="True" Text="Add New"
onclick="btnAddNewRecord_Click" />
</ItemTemplate>
</asp:FormView>
Page Load (only create parameter for email if in insert mode)
protected void Page_Load(object sender, EventArgs e)
{
if (formViewNewItem.CurrentMode == FormViewMode.Insert)
{
// Create your ControlParameter
ControlParameter deptParam = new ControlParameter();
deptParam.ControlID = formViewNewItem.FindControl("ddlInsertDepartment").UniqueID;
deptParam.PropertyName = "SelectedValue";
deptParam.Name = "RoleID";
deptParam.Type = TypeCode.String;
// Add it to your SelectParameters collection
dsourceToEmails.SelectParameters.Add(deptParam);
}
OnInserted, once record is successfully added, send email:
protected void testRecord_Inserted(object sender, EventArgs e)
{
DataView dvToEmails = (DataView)dsourceToEmails.Select(DataSourceSelectArguments.Empty);
string emailsTo = (string)dvToEmails.Table.Rows[0][0];
emailsTo = emailsTo.TrimEnd(',');
string networkUserName = Page.User.Identity.Name;
string emailUserName = networkUserName.Substring(12);
DropDownList departmentSelection = (DropDownList)formViewNewItem.FindControl("ddlInsertDepartment");
var message = new MailMessage();
var client = new SmtpClient();
message.From = new MailAddress("test#abc.com", "Task Tracker");
message.To.Add(emailsTo);
message.Subject = "New Project assigned for " + departmentSelection.SelectedValue;
message.Body = "A new task has been assigned.
<br /><br /><b>Entered by:</b> " + emailUserName;
message.IsBodyHtml = true;
client.Send(message);
}
Got the answer to this...I had to move the SqlDataSource to the InsertItemTemplate, and then use the FindControl method in the OnInserted code to find the SqlDataSource that I had moved, but all worked as it should after all of that.
I have a problem. I have created asp.net web page in c#. I created it using the default master page that visuals studio gives you. There in register.aspx there is a textbox for username like tihs:
<asp:Label ID="UserNameLabel" runat="server" AssociatedControlID="UserName">User Name:</asp:Label>
<asp:TextBox ID="UserName" runat="server" CssClass="textEntry"></asp:TextBox>
<asp:RequiredFieldValidator ID="UserNameRequired" runat="server" ControlToValidate="UserName"
CssClass="failureNotification" ErrorMessage="User Name is required." ToolTip="User Name is required."
ValidationGroup="RegisterUserValidationGroup">*</asp:RequiredFieldValidator>
In cs folder, under the button i put a code that put the registered user into database, but it cannot find the variable of text box. What is the problem here?
protected void RegisterUser_CreatedUser(object sender, EventArgs e)
{
//FormsAuthentication.SetAuthCookie(RegisterUser.UserName, false
//string continueUrl = RegisterUser.ContinueDestinationPageUrl;
//if (String.IsNullOrEmpty(continueUrl))
//{
// continueUrl = "~/";
//}
//Response.Redirect(continueUrl);
try
{
SqlConnection objcon = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ToString());
DataTable objdatatable = new DataTable();
string validationquery = "select * from Uporabniki where username=`" + UserName.Text + "`";
SqlDataAdapter objdavalidate = new SqlDataAdapter(validationquery, objcon);
objdavalidate.SelectCommand.CommandType = CommandType.Text;
objdavalidate.Fill(objdatatable);
if (objdatatable.Rows.Count > 0)
{
...
I have a page with gridview in it.
My gridview shows the products Information and Admin can Edit gridviews columns.
Two of my columns show the brand name and category name for each product;
I use lables in ItemTemplate tag in my grid view to show these two columns value and I use two dropdownlists(branddrop,categorydrop)
in my EditItemTemplate tag for editing these two columns value,when admin select an item in branddrop the categorydrop should show categories name which are related to selected brand name in branddrop.
Brands name in my brand table in database are:
Samsung, Nokia,Sony Ericsson,Apple,LG,HTC....
and my categories name in category table are :
Galaxy Nexus,Galaxy Tab 2 7. 0,Galaxy S3,Asha,Lumia,iPhone,iPad,Xperia Arc,Xperia Neo,Xperia X8,Cookie 3g,Cookie lite,Km555e,Optimus l9,Optimus elite,Optimus g,wt18i,w8,500,n8...
When I click the Edit button, first item in the branddrop is Equal to brandlable.
Text in ItemTemplate and it works fine my problem is the first item in category drop is not Equal to categorylable.text in ItemTemplate and the category drop does not show the related categories name to brandname.for every product it shows iphone and ipad so I have to select another items in branddrop and then select again the related brandname which is related to that product then the categorydrop can show the list of related categories name.I tried to use brandDrop_SelectedIndexChanged and GridView1_RowEditing but it is not work. I dont know how to solve it.
this is my first code:
<asp:TemplateField HeaderText="brand name">
<ItemTemplate>
<asp:Label ID="brandname" runat="server" Text='<%#Eval("brand_name") %>'></asp:Label>
<asp:Label ID="idfrombrand" runat="server" Text='<%#Eval("idfrombrands") %>' Visible="false"></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:Label ID="br" runat="server" Text='<%# Eval("idfrombrands") %>' Visible="false"></asp:Label><%--OnSelectedIndexChanged="brandDrop_SelectedIndexChanged" --%>
<asp:DropDownList ID="brandDrop" runat="server" DataTextField="brand_name" DataValueField="id" DataSourceID="SqlDataSource4" AutoPostBack="true" OnSelectedIndexChanged="brandDrop_SelectedIndexChanged" >
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource4" runat="server" ConnectionString="<%$ ConnectionStrings:mobile_storeConnectionString2 %>" SelectCommand="select [id],[brand_name] from [brands]" ></asp:SqlDataSource>
</EditItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="category name">
<ItemTemplate>
<asp:Label ID="catname" runat="server" Text='<%# Eval("category_name") %>'></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:Label ID="OldCatName" runat="server" Text='<%# Eval("idfromCategories") %>' Visible="false"></asp:Label>
<asp:DropDownList ID="categoryDrop" runat="server" AutoPostBack="true" DataTextField="category_name" DataValueField="id" DataSourceID="SqlDataSource3"> <%-- --%>
</asp:DropDownList>
<asp:Label ID="cat" runat="server" Text='<%# Eval("idfromCategories") %>' Visible="false" ></asp:Label>
<asp:SqlDataSource ID="SqlDataSource3" runat="server" ConnectionString="<%$ ConnectionStrings:mobile_storeConnectionString2 %>" SelectCommand="select [category_name],[id],[idfrombrands] from [categories] where idfrombrands=#idfrombrands " >
<SelectParameters>
<asp:ControlParameter ControlID="brandDrop"
Name="idfrombrands" PropertyName="SelectedValue" Type="Int32" />
</SelectParameters>
</asp:SqlDataSource>
</EditItemTemplate>
</asp:TemplateField>
this is my code behind for GridView1_RowDataBound and GridView1_RowUpdating:
protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
int brand=0;
int category=0;
//Drop Brand--------------------------------------
DropDownList list1 = (DropDownList)GridView1.Rows[e.RowIndex].FindControl("brandDrop");
Label lbl = (Label)GridView1.Rows[e.RowIndex].FindControl("br");
if (list1.SelectedItem.Value != null)
{
brand = Convert.ToInt32(list1.SelectedItem.Value);//NewIdFromBrand
}
else
{
brand = Convert.ToInt32(lbl.Text);
}
//Drop Category----------------------------------------
DropDownList list2 = (DropDownList)GridView1.Rows[e.RowIndex].FindControl("categoryDrop");
Label lbl2 = (Label)GridView1.Rows[e.RowIndex].FindControl("OldCatName");
//int NewIdFromBrand2 = -1;
if (list2.SelectedItem.Value != null)
{
category = Convert.ToInt32(list2.SelectedItem.Value);//NewIdFromBrand2
}
else
{
category = Convert.ToInt32(lbl2.Text);
}
//Photo-------------------------------------------
string photoname = System.Guid.NewGuid().ToString();
GridViewRow row = GridView1.Rows[e.RowIndex];
FileUpload fileUpload = row.FindControl("FileUploadimg") as FileUpload;
Label lbl3 = (Label)GridView1.Rows[e.RowIndex].FindControl("oldImage");
if (fileUpload != null && fileUpload.HasFile)
{
fileUpload.SaveAs(Server.MapPath("~/P_Image") + photoname + fileUpload.FileName);
SqlDataSource1.UpdateParameters["path"].DefaultValue = "~/P_Image" + photoname + fileUpload.FileName;
}
else
{
SqlDataSource1.UpdateParameters["path"].DefaultValue = lbl3.Text;//oldImage.Text;
}
int prid = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value);
SqlConnection cn = new SqlConnection();
cn.ConnectionString = "server = . ; database = mobile_store ; Trusted_Connection=true";
DataTable tb = new DataTable();
SqlCommand cmd = new SqlCommand();
cmd.Connection = cn;
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "UpdateProduct";
cmd.Parameters.AddWithValue("#brandid", brand );
cmd.Parameters.AddWithValue("#catid", category );
cmd.Parameters.AddWithValue("#pid", prid);
try
{
cn.Open();
cmd.ExecuteNonQuery();
SqlDataSource1.DataBind();
}
catch (Exception ex2)
{
}
finally { cn.Close(); }
//GridView1.EditIndex = -1;
//GridView1.DataBind();
}
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
//check if is in edit mode
if ((e.Row.RowState & DataControlRowState.Edit) > 0)
{
DataRowView dRowView1 = (DataRowView)e.Row.DataItem;
if (e.Row.RowType == DataControlRowType.DataRow)
{
if ((e.Row.RowState & DataControlRowState.Edit) > 0)
{
DropDownList ddlStatus = (DropDownList)e.Row.FindControl("brandDrop");
ddlStatus.SelectedValue = dRowView1["brandId"].ToString();
DropDownList ddlStatus2 = (DropDownList)e.Row.FindControl("categoryDrop");
ddlStatus2.SelectedValue = dRowView1["categoryID"].ToString();
//Label1.Text = ddlStatus.SelectedValue;
}
}
}
}
}
Thank you so much Abide Masaraure.you helped me a lot.
I deleted grideview_rowediting and braddrop_selectedIndexChange event And just added two lines to my GridView1_RowDataBound event.
SqlDataSource sq = (SqlDataSource)e.Row.FindControl("SqlDataSource3");
sq.SelectParameters["idfrombrands"].DefaultValue = dRowView1["brandId"].ToString();
now my event is like this:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
//check if is in edit mode
if ((e.Row.RowState & DataControlRowState.Edit) > 0)
{
DataRowView dRowView1 = (DataRowView)e.Row.DataItem;
if (e.Row.RowType == DataControlRowType.DataRow)
{
if ((e.Row.RowState & DataControlRowState.Edit) > 0)
{
DropDownList ddlStatus = (DropDownList)e.Row.FindControl("brandDrop");
ddlStatus.SelectedValue = dRowView1["brandId"].ToString();
DropDownList ddlStatus2 = (DropDownList)e.Row.FindControl("categoryDrop");
ddlStatus2.SelectedValue = dRowView1["categoryID"].ToString();
SqlDataSource sq = (SqlDataSource)e.Row.FindControl("SqlDataSource3");
sq.SelectParameters["idfrombrands"].DefaultValue = dRowView1["brandId"].ToString();
}
}
}
}
}
Eureka!!!.You owe me a cup of coffee.I replicated your problem and realized after two hours that you need to actually hook to your index selected changed event.The trick is to use the naming container property to locate your drop downs,they think are pretty hidden ,but the sender argument enables us to expose them when dropband dropdown fires. And presto everything works like a charm.
Use this code snipet in your selected changed event.
protected void dropBand_SelectedIndexChanged(object sender, System.EventArgs e)
{
DropDownList dropBand = (DropDownList)sender;
SqlDataSource dsc = (SqlDataSource)dropBand.NamingContainer.FindControl("SqlDataSource3");
DropDownList categoryDrop = (DropDownList)dropBand.NamingContainer.FindControl("categoryDrop");
dsc.SelectParameters("BrandID").DefaultValue = dropBand.SelectedValue;
categoryDrop.DataBind();
}
I can send you a zip file of the demo this time if you happen to continue having issue.Happy Coding!!!.
I need to see your code you are using in your selected index changed event.
The following cascading drop down technique will take away all the suffering you have in trying to hook up the parent and its children...I use this wonderful feature in the Ajax control toolkit in all my projects.You can use any data retrieval method you want as long it returns an array.I am using linq in this example for data retrieval.
Assuming I have tables named Brand and Model and classes : Brand and Model and collections: Brands and Models
In 'YourWebServicePath.asmx' (Web service file)
<WebMethod()> _
Public Function GetBrands(knownCategoryValues As String, category As String) As CascadingDropDownNameValue()
Dim result = From b As Bands In Brand.Brands Select New CascadingDropDownNameValue(b.BrandDesc, b.BrandID.ToString())
Return result.ToArray()
End Function
<WebMethod()> _
Public Function GetModels(knownCategoryValues As String, category As String) As CascadingDropDownNameValue()
Dim brandID As Guid
Dim brandValues As StringDictionary = AjaxControlToolkit.CascadingDropDown._
ParseKnownCategoryValuesString(knownCategoryValues)
brandID = New Guid(brandValues("Brand"))
Dim result = From m As Models In Model.GetModels() Where m.brandID = brandID Select New CascadingDropDownNameValue(m.ModelDesc,
_ m.ModelID.ToString())
Return result.ToArray()
End Function
MarkUp
<%# Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<EditItemTemplate>
<asp:DropDownList ID="dropBrand" runat="server" AutoPostBack="true" >
</asp:DropDownList>
<cc1:CascadingDropDown ID="BrandCascadingDropDown"
runat="server"
Category="Brand"
TargetControlID="dropBrand"
PromptText="-Select Brand-"
LoadingText="Loading Brands.."
ServicePath="YourWebServicePath.asmx"
ServiceMethod="GetBrands">
</cc1:CascadingDropDown>
</EditItemTemplate>
<EditItemTemplate>
<asp:DropDownList ID="dropModel" runat="server" AutoPostBack="true" >
</asp:DropDownList>
<cc1:CascadingDropDown ID="ModelCascadingDropDown"
runat="server"
Category="Model"
TargetControlID="dropModel"
ParentControlID="dropBrand"
PromptText="-Select Model-"
LoadingText="Loading Models.."
ServicePath="YourWebServicePath.asmx"
ServiceMethod="GetModels" >
</cc1:CascadingDropDown>
And thats all you need.No need of wiring the events.And voila! let the toolkit perform the magic.
To use the above code i gave you in a row editing event you have to modify it like so.Then those objects won't be null.
protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
GridView testgrid = (GridView)(sender);
testgrid.EditIndex = e.NewEditIndex;
testgrid.DataBind();
DropDownList dropBand = (DropDownList)testgrid.Rows[e.NewEditIndex].FindControl("ddlProducts");
//
}
Something is definitely happening in your page cycle and is keeping on biting you.I suggest zip an mdf of your database and the offending aspx page and let me tackle it from here if you don't get it to work.Never give up.
I have a repeater with a DropDownList in it. I set the datasource of this list in the itembound event en set the selectedindex. When I debug the selectedindex is set, but when the page is done loading for all the item the default item is selected.
This is my code:
protected void Repeater1_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
var ddl = (DropDownList)e.Item.FindControl("DataFeedItems");
ddl.DataSource = FilterDropDownData();
ddl.DataTextField = "ColumnName";
ddl.DataValueField = "ColumnName";
ddl.DataBind();
ddl.SelectedValue = "Select";
ddl.SelectedIndex = 28;
}
protected DataTable FilterDropDownData()
{
var importedFeedColums = I make the table here;
DataRow newRow = importedFeedColums.NewRow();
newRow[0] = "Selecteren";
importedFeedColums.Rows.Add(newRow);
return importedFeedColums;
}
I Als tried to using the Databound even of the dropdown list, but this didnt work either:
protected void DataFeedItems_DataBound(object sender, System.EventArgs e)
{
var ddl = (DropDownList) (sender);
ddl.SelectedValue = "Selecteren";
ddl.Items[28].Selected = true;
}
<asp:Repeater ID="Repeater1" runat="server"
onitemdatabound="Repeater1_ItemDataBound">
<ItemTemplate>
<li>
<label><%# DataBinder.Eval(Container.DataItem, "ColumnName") %></label>
<asp:DropDownList ID="DataFeedItems" ClientIDMode="Static" runat="server" DataSource='<%# FilterDropDownData() %>'
DataTextField="ColumnName" DataValueField="ColumnName" OnDataBound="DataFeedItems_DataBound" >
</asp:DropDownList>
<input id="Hidden1" runat="server" clientidmode="Static" type="hidden" value='<%# DataBinder.Eval(Container.DataItem, "ColumnName") %>' />
</li>
</ItemTemplate>
</asp:Repeater>
When I post the form I can get the selectedvalue and text of each DropDownList. What am I doing wrong
What does FilterDropDownData() return?
Have you tried this?
ddl.Items.FindByValue("Selecteren").Selected = true;
or
ddl.Items.FindByText("Selecteren").Selected = true;
This approach will fail since a drop-down can not have multiple items selected. And setting the "Selected = true" will do exactly the same.
Only way you can set an item as selected is by using the SelectedIndex property of DropDownList.
Ex:ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByValue("Selecteren"));