1. CS 3870
Web User Control
Events

2. Adding Items to Shopping Bag
DataTable bag = (DataTable)Session["Prog7_Bag"]; DataRow row = bag.NewRow(); row[0] = txtID.Text; row[1] = txtName.Text; row[2] = txtQuantity.Text; //row[3] = txtPrice.Text; //row[4] = txtSubTotal.Text; row[3] = double.Parse(txtPrice.Text.Replace("$", "")); row[4] = double.Parse(txtSubTotal.Text.Replace("$", ""));

3. Public Event
Define event
Raise event
Handle event

4. TextChanged for txtQuantity
TextChanged event is defined by for txtQuantity
Raised when the text changed
We only need to handle it
Inside Class Prog7_ShoppingItem
AutoPostBack to True

5. TextChanged for txtQuantity
protected void txtQuantity_TextChanged(object sender, EventArgs e) {
int quantity;
if(int.TryParse(txtQuantity.Text, out quantity) && quantity >= 0)
// update the object and display new cost
_theQuantity = quantity;
_theCost = _theQuantity * _thePrice;
lblMsg.Text = "";
txtCost.Text = string.Format("{0:C}", _theCost); }
else
// Error message on label and clear Cost
txtCost.Text = “”
lblMessage.Text = “Invalid”

6. Checkout.aspx
The total cost not updated when one ShoppingItem has changed. We need an event!

7. Define Event
VB.NET
Public Event ItemChanged(ByVal x As Prog7_ShoppingItem,
ByVal valid As Boolean) C#
//Declaration of delegate.
public delegate void ItemChangedHandler(Prog7_ShoppingItem x,
bool valid);
//Instance of delegate used in declaring event.
public event ItemChangedHandler ItemChanged;

8. Raise Event protected void txtQuantity_TextChanged(. . .) {
int quantity;
if(int.TryParse(txtQuantity.Text, out quantity) &&
quantity >= 0)
// update the object and display new cost
ItemChanged(this, true); }
else
// Error message on label and clear Cost
ItemChanged(this, false);

9. Event Handler
//Handler for an item quantity changing. private void HandleChangeEvent(Prog7_ShoppingItem x, bool valid) { if(valid) } else txtTotal.Text = "";

10. private void HandleChangeEvent(Prog7_ShoppingItem x, bool valid) { if (valid) DataTable theTable = (DataTable)Session["Prog5_Bag"]; double total = 0; DataRow row; for (int i = 0; i < theTable.Rows.Count; i++) row = theTable.Rows[i]; if (row[0].ToString() == x.TheID) row[2] = x.TheQuantity; row[4] = x.TheCost; } total += double.Parse(row[4].ToString()); txtTotal.Text = string.Format("{0:C}", total); else txtTotal.Text = "";

11. Add Event Handler
// Page Checkout protected void Page_Load(object sender, EventArgs e) { for (int i = 0; i < theTable.Rows.Count; i ++) item.ItemChanged += HandleChangeEvent; Panel1.Controls.Add(item); }

12. Page Shopping.aspx
Focus must be correct at all times