Understanding ItemsSource and DataContext in a DataGrid
- by Ben McCormack
I'm trying to understand how the ItemsSource and DataContext properties work in a Silverlight Toolkit DataGrid. I'm currently working with dummy data and trying to get the data in the DataGrid to update when the value of a combo box changes.
My MainPage.xaml.vb file currently looks like this:
Partial Public Class MainPage
Inherits UserControl
Private IssueSummaryList As List(Of IssueSummary)
Public Sub New()
GetDummyIssueSummary("Day")
InitializeComponent()
dgIssueSummary.ItemsSource = IssueSummaryList
'dgIssueSummary.DataContext = IssueSummaryList '
End Sub
Private Sub GetDummyIssueSummary(ByVal timeInterval As String)
Dim lst As New List(Of IssueSummary)()
'Generate dummy data for lst '
IssueSummaryList = lst
End Sub
Private Sub ComboBox_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs)
Dim cboBox As ComboBox = CType(sender, ComboBox)
Dim cboBoxItem As ComboBoxItem = CType(cboBox.SelectedValue, ComboBoxItem)
GetDummyIssueSummary(cboBoxItem.Content.ToString())
End Sub
End Class
My XAML currently looks this for the DataGrid:
<sdk:DataGrid x:Name="dgIssueSummary" AutoGenerateColumns="False" >
<sdk:DataGrid.Columns>
<sdk:DataGridTextColumn Binding="{Binding ProblemType}" Header="Problem Type"/>
<sdk:DataGridTextColumn Binding="{Binding Count}" Header="Count"/>
</sdk:DataGrid.Columns>
</sdk:DataGrid>
The problem is that if I set the value of the ItemsSource property of the data grid equal to IssueSummaryList, it will display the data when it loads, but it won't update when the underlying IssueSummaryList collection changes. If I set the DataContext of the grid to be IssueSummaryList, no data will be displayed when it renders.
I must not understand how ItemsSource and DataContext are supposed to function, because I expect one of those properties to "just work" when I assign a List object to them. What do I need to understand and change in my code so that as data changes in the List, the data in the grid is updated?
