In Technique when creating control dynamically in a Page Load eventhandler these controls will retain their ViewState after the
PostBack, but what if controls created dynamically at runtime in a
Button Click event handler instead of Page Load event then on
PostBack these controls ViewState are lost.To persists the
ViewState of these child controls we will recreate these controls
again on a PostBack in overrideable CreateChildControls() Method
which is called whenever
ASP.NET needs to create these WebControl in a Control Tree.
// Add TextBoxes Control to Placeholder private void CreateTextBoxes()
{ for (int counter = 0; counter <= NumberOfControls; counter++)
{ TextBox tb = new TextBox();
tb.Width = 150;
tb.Height = 18;
tb.TextMode = TextBoxMode.SingleLine;
tb.ID = "TextBoxID" + (counter + 1).ToString();
// add some dummy data to textboxes
tb.Text = "Enter Title " + counter;
phTextBoxes.Controls.Add(tb);
phTextBoxes.Controls.Add(new LiteralControl("<br/>"));
}
}
In CreateTextBoxes method I loop through ‘n’ numbers of controls that we wants to create dynamically in phTextBoxes placeholder.
// Create TextBoxes on PostBack.
protected override void CreateChildControls()
{
// Here we are recreating controls to persist the ViewState on every post back
if (Page.IsPostBack)
{
NumberOfControls += 1;
CreateTextBoxes();
}
else
{
CreateTextBoxes();
// Increase the control value to 1
NumberOfControls = 0;
}
}
CreateChildControls method, here we are recreating control on every
PostBack. If the page is created the first time we just create these
controls and save 1 in the ViewState so we know that we have created
these controls and assigned the controls id to 1.
// Increase the counter when button is clicked and add to view
state
protected void btnAddTitle_Click(object sender, EventArgs e)
{
NumberOfControls += 1;
}
In button event handler we just increase the counter by 1, and save its value to ViewState for later retrieval.
Once we have created these controls on ASP.NET page, retrieving data from these dynamically created controls is easy by using FindControl method.
// Read TextBoxes Data
private void ReadTextBoxes()
{
int n = NumberOfControls;
for (int i = 0; i <>
{
string boxName = "TextBoxID" + (i + 1).ToString();
TextBox tb = phTextBoxes.FindControl(boxName) as TextBox;
strValue += tb.Text +”\n”;
}
}
