DataContext on the Mortgage Home Page

In our last post we covered integrating the database CRUD operations through our MortDB DataContext class. In this post we get to see how simple working with a DataContext can be.

The MortgageHome Page

In a previous post we stopped just short of diving into the MortgageHome.xaml's code behind.

Here is the code behind:

namespace MortCalc
{
    /// <summary>
    /// Code Behind for MortgageHome.xaml
    /// </summary>
    public partial class MortgageHome : Page
    {

        public MortgageHome()
        {
            InitializeComponent();
        }

        private void Amortize_Button_Click(object sender, RoutedEventArgs e)
        {
            //error message tell them to select a mortgage
            if (mortgageListBox.SelectedItem == null)
            {
                MessageBoxResult result = MessageBox.Show(
                    (Window)Parent, "Please Select a Mortgage.",
                    "Error", MessageBoxButton.OK, 
                    MessageBoxImage.Error);
            } else{
                // View Mortgage Amortization Report
                MortgageReportPage mortgageReportPage = new 
                    MortgageReportPage(mortgageListBox.SelectedItem);
                this.NavigationService.Navigate(mortgageReportPage);
            }
        }

        private void New_Button_Click(object sender, RoutedEventArgs e)
        {
            // View Mortgage Amortization Report
            MortgageReportPage mortgageReportPage = 
                new MortgageReportPage();
            this.NavigationService.Navigate(mortgageReportPage);
        }

        private void Page_Loaded(object sender, RoutedEventArgs e)
        {
            var results = from m in DBApi.DB.mortDB.Mortgage
                            select m;

            mortgageListBox.ItemsSource = results.ToList();
        }
    }
}

When looking at the form there are 3 main things that it needs to accomplish:

1. Load the Names of the Mortgages
2. Create a new Mortgage
3. Amortize a selected Mortgage

Load the Names of the Mortgages

The Mortgage Names are loaded into the Listbox component.

<ListBox Name="mortgageListBox"  DisplayMemberPath="Name" FontSize="18" />

We can see that DisplayMemberPath is set to "Name". "Name" in this context makes little sense.

Name is a property in the Mortgage class. Knowing this we can now make sense of the Page_Loaded event function.

private void Page_Loaded(object sender, RoutedEventArgs e)
{
    var results = from m in DBApi.DB.mortDB.Mortgage
                    select m;

    mortgageListBox.ItemsSource = results.ToList();
}

The LINQ to SQL code:

var results = from m in DBApi.DB.mortDB.Mortgage select m;

is doing a SQL like query from the Mortgage table in our database, in code. This is equivalent to the following T- SQL:

SELECT *
FROM Mortgage

We just avoided creating a connection, sending a query, iterating through a result set, ect...

Now all that's left is to bind the results to the ListBox.

mortgageListBox.ItemsSource = results.ToList();

By binding the data we avoided for loops of loading details into the list box and matching names to objects located globally in the Page class. Data binding is powerful and elegant.

Create a New Mortgage

When the New button is clicked the Click event gets fired per our xaml code.

<Button Grid.Row="0" Grid.Column="0" HorizontalAlignment="Right" Click="New_Button_Click" Style="{StaticResource buttonStyle}">
    New
</Button>

Here is the event click function:

private void New_Button_Click(object sender, RoutedEventArgs e)
{
    // View Mortgage Amortization Report
    MortgageReportPage mortgageReportPage = new MortgageReportPage();
    this.NavigationService.Navigate(mortgageReportPage);
}

All we are doing here is navigating to the new page. We instantiate the Page object and tell our NavigationWindow class to Navigate to it. All specifying and saving of data will take place in this new Page.

Amortize a selected Mortgage

When someone selects an existing Mortgage we need a way to tell the MortgageReportPage which record we are working on.

private void Amortize_Button_Click(object sender, RoutedEventArgs e)
{
    //error message tell them to select a mortgage
    if (mortgageListBox.SelectedItem == null)
    {
        MessageBox.Show((Window)Parent, 
            "Please Select a Mortgage.",
            "Error", MessageBoxButton.OK, MessageBoxImage.Error);
    } else{
        // View Mortgage Amortization Report
        MortgageReportPage mortgageReportPage = new MortgageReportPage
            (mortgageListBox.SelectedItem);
            this.NavigationService.Navigate(mortgageReportPage);
    }
}

Check to make sure they selected something and if not let them know they need to.

The only way this Navigation to the MortgageReportPage differs from the last method is the passing in of the ListBox's selected item. I am not operating on the value at all and I am not casting as a Mortgage. Very Simple.

The next post will be dealing with the MortgageReport Page and how it binds data in the Mortgage class to the GUI components.


Download the Code Here