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Placeholder losing data after postback

I'm reading a list of id numbers from a database table into a placeholder textbox but however; if I do a button click the data is removed.
protected void btnSearch_Click(object sender, EventArgs e)
{
while (myReader.Read())
{
TextBox txt = new TextBox();
txt.Text = (string)myReader["idNumber"];
txt.ID = "txt" + i;
txt.ReadOnly = true;
ContentPlaceHolder1.Controls.Add(txt);
ContentPlaceHolder1.Controls.Add(new LiteralControl(" "));
i++;
}
}

This is a common problem when working with dynamically added controls in web forms (especially if you're coming from a winforms background). Pages in ASP.NET Web Forms are stateless, and reconstructed on each postback. Therefore, if you add a control to a page during a server event, you'll also have to add it to the page on subsequent Page loads if you want it to appear. You can accomplish this with something similar to the following:
protected List<Control> ControlCache
{
get => (List<Control>)(Session["cachedControlsForPageX"] = (Session["cachedControlsForPageX"] as List<Control>) ?? new List<Control>());
set => Session["cachedControlsForPageX"] = value;
}
/* If you can't use C# 7's expression bodied property accessors, here's the equivalent in blocks:
protected List<Control> ControlCache
{
get { return (List<Control>)(Session["cachedControlsForPageX"] = (Session["cachedControlsForPageX"] as List<Control>) ?? new List<Control>()); }
set { Session["cachedControlsForPageX"] = value; }
}
*/
protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack)
{
foreach (var control in ControlCache)
{
ContentPlaceHolder1.Controls.Add(control);
ContentPlaceHolder1.Controls.Add(new LiteralControl(" "));
}
}
else
ControlCache = null;
}
protected void btnSearch_Click(object sender, EventArgs e)
{
while (myReader.Read())
{
TextBox txt = new TextBox();
txt.Text = (string)myReader["idNumber"];
txt.ID = "txt" + i;
txt.ReadOnly = true;
ContentPlaceHolder1.Controls.Add(txt);
ContentPlaceHolder1.Controls.Add(new LiteralControl(" "));
ControlCache.Add(txt);
i++;
}
}

C# Drop Down List Not Trigger index changing

I select one value on the ddl , and it does not show the products in the page. The selected value remains binded but the page is blank.
Also , if I just call function getCat() without using if(!ispostback). When i load the page the drop down list is stuck on the first value , but it shows the products in page.
Drop Down List:
<asp:dropdownlist runat="server" id="ddcateg" AutoPostBack="true" onselectedindexchanged="Ddcateg_SelectedIndexChanged"></asp:dropdownlist>
This is the implementation:
protected void Page_Load(object sender, EventArgs e)
{
//afisare();
if (!IsPostBack)
{
getCateg();
}
}
public void getCateg()
{
ProdusTipModel model = new ProdusTipModel();
FarmacieEntities db = new FarmacieEntities();
var lizt = (from c in db.ProdusTips select c).ToList();
ddcateg.DataSource = lizt;
ddcateg.DataValueField = "ID";
ddcateg.DataTextField = "Name";
ddcateg.DataBind();
ddcateg.SelectedIndexChanged += Ddcateg_SelectedIndexChanged;
}
public void afisare2(List<Produ> z)
{
ProdusModel mdl = new ProdusModel();
foreach (var produs in z)
{
Panel produsePnl = new Panel();
ImageButton imageButton = new ImageButton();
produsePnl.BorderColor = Color.AliceBlue;
Label lblNume = new Label();
Label lblPret = new Label();
produsePnl.BorderStyle = BorderStyle.Groove;
produsePnl.BorderColor = Color.LightSkyBlue;
imageButton.ImageUrl = "~/Img/Produse/" + produs.Image;
imageButton.CssClass = "imgProdus";
imageButton.PostBackUrl = "~/Pages/PaginaProdus.aspx?id=" + produs.ID;
lblNume.Text = produs.Name;
lblNume.CssClass = "numeProd";
lblPret.Text = produs.Price + "lei";
lblPret.CssClass = "produsPret";
produsePnl.Controls.Add(imageButton);
produsePnl.Controls.Add(new Literal { Text = "<br /" });
produsePnl.Controls.Add(lblNume);
produsePnl.Controls.Add(new Literal { Text = "<br /" });
produsePnl.Controls.Add(lblPret);
pnlProduse.Controls.Add(produsePnl);
}
}
private void Ddcateg_SelectedIndexChanged(object sender, EventArgs e)
{
DropDownList selectedList = (DropDownList)sender;
int selectedLit = Convert.ToInt32(selectedList.SelectedValue);
ProdusModel mdl = new ProdusModel();
List<Produ> list = mdl.GetProdCateg(selectedLit).ToList();
afisare2(list);
}

Your problem could be that your code behind method is private:
private void Ddcateg_SelectedIndexChanged(object sender, EventArgs e)
Try making it protected or public so it can be seen by the aspx page.

ASP.NET Textbox losing values after postback which were set during editing

There's a gridview in my program whose row's data is to be loaded in textboxes if edit is clicked.
Here is the code where I'm filling the data in textboxes after edit is clicked
protected void GV_Parameters_RowEditing(object sender, GridViewEditEventArgs e)
{
GV_Parameters.EditIndex = e.NewEditIndex;
int index = e.NewEditIndex;
IsEditing = true;
Label lbl_frmdate = (Label)GV_Parameters.Rows[index].FindControl("lbl_frmdate") as Label;
Label lbl_todate = (Label)GV_Parameters.Rows[index].FindControl("lbl_todate") as Label;
EditFromDate = lbl_frmdate.Text.ToUpper();
lbl_frm_edit.Text = EditFromDate;
EditToDate = lbl_todate.Text.ToUpper();
lbl_to_edit.Text = EditToDate;
Label lbl = (Label)GV_Parameters.Rows[index].Cells[3].FindControl("lbl_Is_holiday");
string is_holiday = lbl.Text;
Label lbl_std_intime = (Label)GV_Parameters.Rows[index].FindControl("lbl_std_intime") as Label;
Label lbl_std_outtime = (Label)GV_Parameters.Rows[index].FindControl("lbl_std_outtime") as Label;
string[] arr_std_intime;
string[] arr_std_outtime;
if (is_holiday != "1")//working day
{
r_work_holiday.SelectedIndex = 0;
IsHoliday = false;
if (lbl_std_intime.Text != "")
{
arr_std_intime = lbl_std_intime.Text.Split(':');
txt_std_TimeInHours.Text = arr_std_intime[0].ToString();
txt_std_TimeInMins.Text = arr_std_intime[1].ToString();
}
if (lbl_std_outtime.Text != "")
{
arr_std_outtime = lbl_std_outtime.Text.Split(':');
txt_std_TimeOutHours.Text = arr_std_outtime[0].ToString();
txt_std_TimeOutMins.Text = arr_std_outtime[1].ToString();
}
}
else
{
IsHoliday = true;
//r_workingday.Checked = false;
//r_holiday.Checked = true;
r_work_holiday.SelectedIndex = 1;
Label lbl_remarks = (Label)GV_Parameters.Rows[index].FindControl("lbl_remarks") as Label;
txt_holiday_desc.Text = lbl_remarks.Text;
}
collapse_state = "expand";
}
There is a radiobutton list who shows the edited row is holiday or working day,
if user changes the selection in radioButtonList, PostBack occurs and this is the time when all of the texboxes turn blank.
protected void r_work_holiday_SelectedIndexChanged(object sender, EventArgs e)
{
if(r_work_holiday.SelectedIndex==0)
{
IsHoliday = false;
}
else
{
IsHoliday = true;
}
collapse_state = "expand";
}
There's no any method in page load who is clearing the textboxes.
protected void Page_Load(object sender, EventArgs e)
{
if (IsEditing)
{
collapse_state = "expand";
}
if (!Page.IsPostBack)
{
BindYears();
}
}
Please help
Update ::
lbl_frm_edit and lbl_to_edit are not getting reset after postback.
The variable EditFromDate and EditToDate are being set by Viewstate

It's been sometime I worked in ASP controls but if I remember correctly, the content in textboxes are generally cleared on every post back by ASP .NET. The state of the textboxes are not saved.
Here is an answer I found while researching this issue.
You could store the value of the textboxes in ViewState and assign them back on the PageLoad event. Something like
txt_std_TimeOutHours.Text = arr_std_outtime[0].ToString();
txt_std_TimeOutMins.Text = arr_std_outtime[1].ToString();
ViewState["TimeOutHours"] = arr_std_outtime[0].ToString();
ViewState["TimeOutMins"] = arr_std_outtime[1].ToString();
And on the PageLoad event you can do this to restore the values.
if(Page.IsPostBack)
{
txt_std_TimeOutHours.Text = ViewState["TimeOutHours"].ToString();
txt_std_TimeOutMins.Text = ViewState["TimeOutMins"].ToString();
}
Hope this helps!

Retrieve value from dynamic dropdownlist in placeholder C#

I have dynamic drop down lists that are created based on what's selected in the list box.. When clicking confirm this is when the drop down lists are created. Clicking save is where I attempt to retrieve the values. However I am unable to retrieve that values that are in the drop down lists.
Code:
protected void btnConfirm_Click(object sender, EventArgs e)
{
int ID = 0;
foreach (string value in values)
{
MyStaticValues.alEdit.Add(value);
CreateEditForm(value, ID);
ID += 1;
}
if (values.count != 0)
{
btnSave.Visible = true;
btnConfirm.Enabled = false;
}
}//End of btnConfirm_Click
protected void CreateEditForm(string Value, int ID)
{//Creates an edit form for the value inserted.
string name = value;
//This part adds a header
phEditInventory.Controls.Add(new LiteralControl("<h2>" + name + "</h2>"));
phEditInventory.Controls.Add(new LiteralControl("<div class=\"clearfix\"></div>"));
//Create a label
Label lblName = new Label();
lblName.Text = "Name";
lblName.ID = "lblName" + ID;
lblName.CssClass = "control-label";
//Create a Drop Down List
DropDownList ddlName = new DropDownList();
ddlName.ID = "ddlName" + ID;
ddlName.CssClass = "form-control";
//Set default N/A Values For Drop Down List
ddlName.Items.Add(new ListItem("N/A", Convert.ToString("0")));
//The Rest of the Values are populated with the database
//Adds the controls to the placeholder
phEditInventory.Controls.Add(lblName);
phEditInventory.Controls.Add(ddlName);
phEditInventory.Controls.Add(new LiteralControl("<div class=\"clearfix\"></div>"));
} //End of CreateEditForm
protected void btnSave_Click(object sender, EventArgs e)
{
string name = "";
try
{
for (int i = 0; i < MyStaticValues.alEdit.Count; i++)
{
string nameID = "ddlName" + i.ToString();
DropDownList ddlName = (DropDownList)phEditInventory.FindControl(nameID);
name = ddlName.SelectedValue.ToString();
}
}
catch (Exception ex)
{
}
phEditInventory.Visible = false;
btnSave.Visible = false;
MyStaticValues.alEdit.Clear();
}//End of btnSave_Click Function

Your problem is that the dynamically created dropdown lists are not maintained on postback. When you click the Save button, a postback occurs, and the page is re-rendered without the dynamically created dropdowns. This link may help.
Maintain the state of dynamically added user control on postback?

'Find and Save' functionality not working

First time poster, long time lurker. I am having some trouble with my ASP.NET page, and I hope someone can help me resolve my issue.
Basically, I have a bunch of checkboxes in a gridview, and two buttons: a 'find' button, and a 'save' button. The 'find' can set the value of the checkbox, but if a user unchecks it, I want to capture that change when the user hits 'save'. Currently, it does not work.
Relevant ASPX:
<%# Page Language="C#" AutoEventWireup="true" EnableViewState="true" CodeBehind="FindTransactions.aspx.cs" Inherits="Basic.FindTransactions" MasterPageFile="~/Trans.Master" %>
Relevant Code Behind here:
Page:
public partial class FindTransactions : System.Web.UI.Page
{
GridView _gridview = new GridView() { ID = "_gridView" };
DataTable _datatable = new DataTable();
Int32 _buyerID = new Int32();
protected void Page_Load(object sender, EventArgs e)
{
}
"Find" button:
protected void Find_Click(object sender, EventArgs e)
{
//truncated
_datatable.Rows.Add(
//filled with other data from a custom object.
);
ViewState["_datatable"] = _datatable;
ViewState["_buyerID"] = _buyerID;
BuildGridView((DataTable)ViewState["_datatable"],(Int32)ViewState["buyerID"]);
}
BuildGridView function:
protected void BuildGridView(DataTable d, Int32 b)
{
_gridview.DataKeyNames = new String[] {"Transaction ID"};
_gridview.AutoGenerateColumns = false;
_gridview.RowDataBound += new GridViewRowEventHandler(OnRowDataBound);
for(Int32 i = 0; i < d.Columns.Count; i++)
{
Boundfield boundfield = new BoundField();
boundfield.DataField = d.Columns[i].ColumnName.ToString();
boundfield.HeaderText = d.Columns[i].ColumnName.ToString();
_gridview.Columns.Add(boundfield);
}
_gridview.DataSource = d;
_gridview.DataBind();
//truncated
Panel1.Controls.Add(_gridview);
}
Row Bound Event handler:
protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
String controlID = "checkBox";
CheckBox c = new CheckBox() { ID = controlID};
c.Enabled = true;
Boolean success;
Boolean v;
success = Boolean.TryParse(e.Row.Cells[8].Text, out v);
e.Row.Cells[8].Controls.Add(c);
if (success)
{
c.Checked = v;
if (c.Checked)
{
//Will uncomment once other things work
//e.Row.Visible = false;
}
}
else
{
c.Checked = false;
}
}
}
All of that works. Here is where it starts to break down:
"Save" button:
protected void Save_Click(object sender, EventArgs e)
{
//Both for troubleshooting and both return 0. (Expected for datatable)
Label1.Text = _gridview.Rows.Count.ToString();
Label2.Text = _datatable.Rows.Count.ToString();
/*truncated
*/
if (grid.Rows.Count == 0)
{
BuildGridView((DataTable)ViewState["infoTable"], (Int32)ViewState["guestID"]);
}
foreach (GridViewRow r in grid.Rows)
{
if (r.RowType == DataControlRowType.DataRow)
{
CheckBox cb = (CheckBox)r.FindControl("checkBox");
if (cb != null && cb.Checked)
{
//This never seems to modify the label.
//Will put code to modify database here.
Label2.Text += "Hi " + r.RowIndex.ToString();
}
}
}
}
After I hit the save button, PostBack occurs and GridView is empty (Rows.Count is 0). ViewState appears to be lost before I get a chance to loop through the GridView rows to determine the checkbox values.
At the end of it all, I just want to capture the status of those checkboxes, changed by user interaction or not, by hitting the 'Save' button.
I found some other articles, but a lot of them haven't worked when I tried implementing the various fixes.
This one seems to be the closest that describes my issue, and the code is structured similarly, but I don't quite understand how to implement the fix: GridView doesn't remember state between postbacks
[New simplified code to illustrate problem:]
namespace GridViewIssue
{
public partial class GridViewNoMaster : System.Web.UI.Page
{
GridView _gridView = new GridView() { ID = "_gridView" };
DataTable _dataTable = new DataTable();
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Find_Click(object sender, EventArgs e)
{
BuildDataTable();
List<String> list = new List<String>();
list.Add("1");
list.Add("User");
list.Add("10/12/2014");
foreach (String s in list)
{
_dataTable.Rows.Add(
list[0],
list[1],
list[2]
);
}
BuildGridView();
//Feedback.Text = _gridView.Rows.Count.ToString();
}
protected void Save_Click(object sender, EventArgs e)
{
Feedback.Text = "Save Clicked, PostBack: " + IsPostBack + ", GridView Row Count: " + _gridView.Rows.Count + ", GridView ViewState: " + _gridView.EnableViewState;
foreach (GridViewRow r in _gridView.Rows)
{
if(r.RowType == DataControlRowType.DataRow)
{
Feedback.Text = "In DataRow type" + _gridView.Rows.Count;
}
}
}
protected void BuildDataTable()
{
_dataTable.Columns.Add("Transaction ID", typeof(String));
_dataTable.Columns.Add("Name", typeof(String));
_dataTable.Columns.Add("Date", typeof(String));
}
protected void BuildGridView()
{
for (Int32 i = 0; i < _dataTable.Columns.Count; i++)
{
BoundField b = new BoundField();
b.DataField = _dataTable.Columns[i].ColumnName.ToString();
b.HeaderText = _dataTable.Columns[i].ColumnName.ToString();
_gridView.Columns.Add(b);
}
_gridView.DataKeyNames = new String[] { "Transaction ID" };
_gridView.AutoGenerateColumns = false;
_gridView.DataSource = _dataTable;
_gridView.DataBind();
Panel1.Controls.Add(_gridView);
}
}
}