Adding and Deleting Data

Write code to modify, delete, and create products

1.Return to the Visual Studio 2008 window in which you were editing the Suppliers application.

2.In the Design View window, in the XAML pane, modify the definition of the productsList control to trap the KeyDown event and invoke an event method called productsList_KeyDown. (This is the default name of the event method.) If IntelliSense does not recognize the KeyDown keyword, try closing and reopening the SupplierInfo. xaml file.

3.In the Code and Text Editor window, add the following code shown in bold type to the productsList_KeyDown method.

private void productsList_KeyDown(object sender, KeyEventArgs e)

{

switch (e.Key)

{

case Key.Enter: editProduct(this.productsList.SelectedItem as Product); break;

case Key.Insert: addNewProduct(); break;

case Key.Delete: deleteProduct(this.productsList.SelectedItem as Product); break;

}

}

This method examines the key pressed by the user. If the user presses the Enter key, the code calls the editProduct method, passing in the details of the product as a parameter. If the user presses the Insert key, the code calls the addNewProduct method to cre-

ate and add a new product to the list for the current supplier, and if the user presses the Delete key, the code calls the deleteProduct method to delete the product. You will write the editProduct, addNewProduct, and deleteProduct methods in the next few

steps.

4. Add the deleteProduct method to the SupplierInfo class, as follows:

private void deleteProduct(Product prod)

{

MessageBoxResult response = MessageBox.Show(“Delete “ + prod.ProductName, “Confirm”, MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No);

if (response == MessageBoxResult.Yes)

{

supplier.Products.Remove(prod);

productsInfo.Remove(prod); this.saveChanges.IsEnabled = true;

}

}

This method prompts the user to confirm that the user really does want to delete the currently selected product. The if statement calls the Remove method of the Products EntitySet<TEntity> property to delete the product from this collection and also removes it from the productsInfo binding list. (This step is necessary to ensure that the display

is kept synchronized with the changes.) Finally, the method activates the saveChanges

button. You will add functionality to this button to send the changes made to the Products EntitySet<TEntity> back to the database in a later step.

There are several approaches you can use for adding and editing products; the columns in the ListView control are read-only text items, but you can create a customized

list view that contains text boxes or other controls that enable user input. However, the simplest strategy is to create another form that enables the user to edit or add the details of a product.

5.On the Project menu, click Add Class. In the Add New Items – Suppliers dialog box, select the Window (WPF) template, type ProductForm.xaml in the Name box, and then click Add.

6.In the Design View window, click the ProductForm form, and in the Properties window, set the ResizeMode property to NoResize, set the Height property to 225, and set the Width property to 515.

7.Add three Label controls, three TextBox controls, and two Button controls to the form. Using the Properties window, set the properties of these controls to the values shown in the following table.

The Supplier Information form should look like this in the Design View window:

8.Double-click the OK button to create an event handler for the click event. In the Code and Text Editor window displaying the ProductForm.xaml.cs file, add the following code shown in bold type.

private void ok_Click(object sender, RoutedEventArgs e)

{

if (String.IsNullOrEmpty(this.productName.Text))

{

MessageBox.Show(“The product must have a name”, “Error”, MessageBoxButton.OK, MessageBoxImage.Error);

return;

}

decimal result;

if (!Decimal.TryParse(this.unitPrice.Text, out result))

{

MessageBox.Show(“The price must be a valid number”, “Error”, MessageBoxButton.OK, MessageBoxImage.Error);

return;

}

if (result < 0)

{

MessageBox.Show(“The price must not be less than zero”, “Error”, MessageBoxButton.OK, MessageBoxImage.Error);

return;

}

this.DialogResult = true;

}

The application will display this form by calling the ShowDialog method. This method

displays the form as a modal dialog box. When the user clicks a button on the form, it will close automatically if the code for the click event sets the DialogResult property.

If the user clicks OK, this method performs some simple validation of the information entered by the user. The Quantity Per Unit column in the database accepts null values,

so the user can leave this field on the form empty. If the user enters a valid product name and price, the method sets the DialogResult property of the form to true. This value is passed back to the ShowDialog method call.

9.Return to the Design View window displaying the ProductForm.xaml file. Select the Cancel button, and in the Properties window, set the IsCancel property to true (select the check box).

If the user clicks the Cancel button, it will automatically close the form and return a

DialogResult value of false to the ShowDialog method.

10.Switch to the Code and Text Editor window displaying the SupplierInfo.xaml.cs file. Add the addNewProduct method shown here to the SupplierInfo class.

private void addNewProduct()

{

ProductForm pf = new ProductForm();

pf.Title = “New Product for “ + supplier.CompanyName; if (pf.ShowDialog().Value)

{

Product newProd = new Product(); newProd.SupplierID = supplier.SupplierID; newProd.ProductName = pf.productName.Text; newProd.QuantityPerUnit = pf.quantityPerUnit.Text;

newProd.UnitPrice = Decimal.Parse(pf.unitPrice.Text); supplier.Products.Add(newProd); productsInfo.Add(newProd);

this.saveChanges.IsEnabled = true;

}

}

The addNewProduct method creates a new instance of the ProductForm form, sets the Title property of this form to contain the name of the supplier, and then calls the ShowDialog method to display the form as a modal dialog box. If the user enters some

valid data and clicks the OK button on the form, the code in the if block creates a new Product object and populates it with the information from the ProductForm instance.

554 Part V Managing Data

The method then adds it to the Products EntitySet<TEntity> for the current supplier and

also adds it to the list displayed in the list view control on the form. Finally, the code activates the Save Changes button. In a later step, you will add code to the click event

handler for this button so that the user can save changes back to the database. 11. Add the editProduct method shown here to the SupplierInfo class.

private void editProduct(Product prod)

{

ProductForm pf = new ProductForm(); pf.Title = “Edit Product Details”; pf.productName.Text = prod.ProductName;

pf.quantityPerUnit.Text = prod.QuantityPerUnit; pf.unitPrice.Text = prod.UnitPrice.ToString();

if (pf.ShowDialog().Value)

{

prod.ProductName = pf.productName.Text; prod.QuantityPerUnit = pf.quantityPerUnit.Text; prod.UnitPrice = Decimal.Parse(pf.unitPrice.Text); this.saveChanges.IsEnabled = true;

}

}

The editProduct method also creates an instance of the ProductForm form. This time, as well as setting the Title property, the code also populates the fields on the form with

the information from the currently selected product. When the form is displayed, the user can edit these values. If the user clicks the OK button to close the form, the code

in the if block copies the new values back to the currently selected product before activating the Save Changes button. Notice that this time you do not need to update the current item manually in the productsInfo list because the Product class notifies the list

view control of changes to its data automatically.

12.Return to the Design View window displaying the SupplierInfo.xaml file. Double-click the Save Changes button to create the click event handler method.

13.In the Code and Text Editor window, add the following code shown in bold to the saveChanges_Click method:

private void saveChanges_Click(object sender, RoutedEventArgs e)

{

try

{

ndc.SubmitChanges(); saveChanges.IsEnabled = false;

}

catch (Exception ex)

{

MessageBox.Show(ex.Message, “Error saving changes”);

}

}