This article covers LINQ to SQL with WPF, and binding the SelectedItem of a
ListBox control.
LINQ is a set of technologies introduced in Visual Studio 2008 and enables you
to work with data from different data sources present in various data formats.
As per the MSDN library, LINQ is "a set of extensions to the .NET Framework that
encompass language-integrated query, set, and transform operations. It extends
C# and Visual Basic with native language syntax for queries and provides class
libraries to take advantage of these capabilities."
Wikipedia has a simpler definition: LINQ is "a Microsoft .NET Framework
component that adds native data querying capabilities to .NET languages."
One of the important implementations of LINQ, LINQ to SQL, gives you a runtime
infrastructure for managing relational data as objects without losing the
ability to perform query operations. LINQ To SQL is one of the approaches in
LINQ through which you can bind any LINQ-enabled data source using SQL syntax.
You can bind to data in a WPF application using LINQ To SQL. Let us see how to
do this.
This article assumes that you are using SQL Server 2008 and have the sample
database Northwind attached to your Oracle instance.
- Create a new WPF application named
LinqToSql.
- Drag and drop a ListBox and a TextBox into
the designer view of MainWindow.xaml. Configure their properties as follows:
<Window
x:Class="LinqToSql.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow"
Height="350"
Width="525"
Loaded="Window_Loaded">
<Grid>
<ListBox
Name="lstNames"
Background="BlanchedAlmond"
Margin="158,20,144,183"
>
</ListBox>
<TextBox
Height="23"
HorizontalAlignment="Left"
Margin="158,236,0,0"
Name="txtName"
VerticalAlignment="Top"
Width="224"
Text="{Binding
SelectedItem.FirstName,
ElementName=lstNames}"
/>
<TextBlock
Height="24"
HorizontalAlignment="Left"
Margin="38,30,0,0"
Name="textBlock1"
Text="Select
an entry:"
VerticalAlignment="Top"
Width="114"
/>
</Grid>
</Window>
- Select Project->Add New Item . Select LINQ
to SQL Classes as the template. Rename the file as Emp. The extension dbml
is automatically added. A dbml file is a database markup language file.
![WPFLinqSQL1.gif]()
Figure 1
- Select Data menu and then select the Add
New Data Sources option.
![WPFLinqSQL2.gif]()
Figure 2
- In the Choose Data Source wizard, select
Database as shown in Figure 3 and click Next.
![WPFLinqSQL3.gif]()
Figure 3
- In the Choose Database Model section,
select DataSet as shown in Figure 4 and click Next.
![WPFLinqSQL4.gif]()
Figure 4
- Specify the connection string details as
shown in Figure 5.
![WPFLinqSQL5.gif]()
Figure 5
- Select Employees from the list of tables
as shown in Figure 6.
![WPFLinqSQL6.gif]()
Figure 6
The data source is added to the Server Explorer.
Open the designer area of the Emp.dbml file. Drag the Employees table from
the Server Explorer to the designer area. This results in the Employee data
class being generated as shown in Figure 7.
![WPFLinqSQL7.gif]()
Figure 7
This also results in the creation of a data context which is named as
EmpDataContext. Figure 8 shows the data context created in the .dbml file.
![WPFLinqSQL8.gif]()
Figure 8
- Save the file.
- Click Project-> Add Class and add a new
class named ObservableEmployee. Add the following code to this class. This
creates an ObservableCollection of employees.
class ObservableEmployee : ObservableCollection<Employee>
{
public ObservableEmployee(EmpDataContext edc)
{
foreach (Employee emp in edc.Employees)
{
this.Add(emp);
}
}
}
- Update the XAML markup in MainWindow.xaml
to set the ITemTemplate and DataTemplate of the ListBox and set the binding
of the TextBox as follows:
<Window
x:Class="LinqToSql.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow"
Height="350"
Width="525"
Loaded="Window_Loaded">
<Grid>
<ListBox
Name="lstNames"
Background="BlanchedAlmond"
Margin="158,20,144,183"
SelectedItem="{Binding
FirstName}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel
Orientation="Horizontal">
<TextBlock
Name="FirstName"
Width="100"
Text="{Binding
Path=FirstName}"></TextBlock>
<TextBlock
Name="LastName"
Width="100"
Text="{Binding
Path=LastName}"></TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBox
Height="23"
HorizontalAlignment="Left"
Margin="158,236,0,0"
Name="txtName"
VerticalAlignment="Top"
Width="224"
Text="{Binding
SelectedItem.FirstName,
ElementName=lstNames}"
/>
<TextBlock
Height="24"
HorizontalAlignment="Left"
Margin="38,30,0,0"
Name="textBlock1"
Text="Select
an entry:"
VerticalAlignment="Top"
Width="114"
/>
</Grid>
</Window>
Here, the ListBox template is set such that it
is bound to a combination of First Name and Last Name columns in the Employees
table of the database. The TextBox in turn is bound to the SelectedItem property
of the ListBox so that whenever a user selects an item from the ListBox, the
first name is displayed in the TextBox.
However, the binding is not done directly, it is done through the LINQ to SQL
class and the ObservableCollection of employees as shown below:
public partial class
MainWindow : Window
{
private static EmpDataContext _empDC = new EmpDataContext();
private ObservableEmployee _knownEmp;
public MainWindow()
{
InitializeComponent();
}
private void
Window_Loaded(object sender, RoutedEventArgs e)
{
// Populate the observable collection of employees from the database
_knownEmp = new ObservableEmployee(_empDC);
// Set this to the
ItemsSource property of the ListBox
this.lstNames.ItemsSource = _knownEmp;
}
}
Save, build, and execute the application. Sample output is shown in Figure
![WPFLinqSQL9.gif]()
Figure 9
Conclusion: This article covered LINQ to SQL with WPF, and binding the
SelectedItem of a ListBox control.