When creating control dynamically in a Page Load event handler 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() the 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 I loop through ‘n’ numbers of controls that we want 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 ViewStateSo we know that we have created.
these controls and assigned the id of the control to 1.
// Increase the counter when the button is clicked and add to view state
protected void btnAddTitle_Click(object sender, EventArgs e)
{
NumberOfControls += 1;
}
In the button event handler, we just increase the counter by one and save its value to ViewState for later retrieval. Once we have created these controls on the ASP.NET page, retrieving data from these dynamically created controls is easy by using the FindControl method.
// Read TextBoxes Data
public int NumberOfControls
{
get
{
if (ViewState["Count"] == null)
{
return 0;
}
return (int)ViewState["Count"];
}
set
{
ViewState["Count"] = value++;
}
}
private void ReadTextBoxes()
{
strValue = string.Empty;
int n = NumberOfControls;
for (int i = 0; i <= NumberOfControls; i++)
{
string boxName = "TextBoxID" + (i + 1).ToString();
TextBox tb = phTextBoxes.FindControl(boxName) as TextBox;
strValue += tb.Text + "\n";
}
Response.Write(strValue);
}