When does the binding on the ItemsSource property generate Items? - wpf

Question

I have added a dialog to my WPF application. Here's the Xaml:
<cs:CarSystemDialog x:Class="CarSystem.CustomControls.EditHotListDialog"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cs="clr-namespace:CarSystem.CustomControls"
DataContext="{Binding Path=HotList, RelativeSource={RelativeSource Self}}"
Height="265"
Loaded="EditHotListDialog_Loaded"
MaxHeight="665"
MaxWidth="1200"
SizeToContent="WidthAndHeight"
cs:ThemeSelector.CurrentThemeDictionary="{Binding Path=TimeOfDayTheme, RelativeSource={RelativeSource Self}}"
Width="850"
WindowStartupLocation="CenterOwner" >
<cs:CarSystemDialog.Resources>
<cs:BooleanToVisibilityConverter x:Key="BoolToVisibility" True="Visible" False="Collapsed" />
<cs:CaseToVisibilityConverter x:Key="CaseToVisibilityConverter" />
</cs:CarSystemDialog.Resources>
<Grid Background="{DynamicResource ContentBackground}" FocusManager.IsFocusScope="True" Name="LayoutRoot">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<TextBlock FontSize="16"
FontWeight="Bold"
Foreground="{DynamicResource TextForeground}"
Grid.Column="0"
Grid.Row="0"
HorizontalAlignment="Right"
Margin="5"
Text="Source:"
VerticalAlignment="Center" />
<TextBox AcceptsTab="False"
AcceptsReturn="False"
BorderBrush="{DynamicResource ControlBorder}"
BorderThickness="2"
FontSize="16"
FontWeight="Bold"
Foreground="{DynamicResource UnfocusedForeground}"
Grid.Column="1"
Grid.Row="0"
Margin="5"
MaxLength="80"
MaxLines="1"
Name="HotListNameBox"
TabIndex="0"
Text="{Binding Path=Name, Mode=TwoWay}"
VerticalAlignment="Center" />
<TextBlock FontSize="16"
FontWeight="Bold"
Foreground="{DynamicResource TextForeground}"
Grid.Column="2"
HorizontalAlignment="Right"
Margin="5"
Text="List Type:"
VerticalAlignment="Center" />
<ComboBox BorderBrush="{DynamicResource PlateInfoBorder}"
DisplayMemberPath="Value"
FontSize="16"
FontWeight="Bold"
Grid.Column="3"
ItemsSource="{Binding Path=ListTypes, RelativeSource={RelativeSource AncestorType={x:Type cs:EditHotListDialog}}}"
Margin="5"
Name="ListTypePicker"
SelectedValue="{Binding Path=ListTypeId, Mode=TwoWay}"
SelectedValuePath="Key"
TabIndex="1" />
<TextBlock FontSize="16"
FontWeight="Bold"
Foreground="{DynamicResource TextForeground}"
Grid.Column="0"
Grid.Row="1"
HorizontalAlignment="Right"
Margin="5"
Text="Domain:"
VerticalAlignment="Center" />
<ComboBox BorderBrush="{DynamicResource PlateInfoBorder}"
DisplayMemberPath="Value"
FontSize="16"
FontWeight="Bold"
Grid.Column="1"
Grid.Row="1"
ItemsSource="{Binding Path=Domains, RelativeSource={RelativeSource AncestorType={x:Type cs:EditHotListDialog}}}"
Margin="5"
Name="DomainPicker"
SelectedValue="{Binding Path=DomainId, Mode=TwoWay}"
SelectedValuePath="Key"
TabIndex="1" />
<StackPanel Grid.Column="0"
Grid.ColumnSpan="4"
Grid.Row="2"
HorizontalAlignment="Center"
Orientation="Horizontal">
<Button Background="{DynamicResource ButtonBackground}"
Click="OkButton_Click"
Content="OK"
FontSize="18"
FontWeight="Bold"
Foreground="{DynamicResource ButtonForeground}"
Height="50"
IsDefault="True"
IsEnabled="{Binding Path=CanSave, RelativeSource={RelativeSource AncestorType={x:Type cs:EditHotListDialog}}}"
Margin="5"
Name="OkButton"
Width="100"/>
<Button Background="{DynamicResource ButtonBackground}"
Content="Cancel"
FontSize="18"
FontWeight="Bold"
Foreground="{DynamicResource ButtonForeground}"
Height="50"
IsCancel="True"
Margin="5"
Name="CancelButton"
Width="100" />
</StackPanel>
</Grid>
</cs:CarSystemDialog>
And here's the code behind:
public partial class EditHotListDialog : CarSystemDialog, INotifyPropertyChanged {
public static readonly DependencyProperty CanSaveProperty =
DependencyProperty.Register( "CanSave", typeof( bool ), typeof( EditHotListDialog ), new PropertyMetadata( false ) );
public static readonly DependencyProperty HotListProperty =
DependencyProperty.Register( "HotList", typeof( HotListViewModel ), typeof( EditHotListDialog ),
new PropertyMetadata( null, new PropertyChangedCallback( OnHotListChanged ) ) );
public bool CanSave {
get { return (bool) GetValue( CanSaveProperty ); }
set { SetValue( CanSaveProperty, value ); }
}
public ObservableCollection<ItemChoice<int?>> Domains { get; set; }
public HotListViewModel HotList {
get { return (HotListViewModel) GetValue( HotListProperty ); }
set { SetValue( HotListProperty, value ); }
}
public ObservableCollection<ItemChoice<int?>> ListTypes { get; set; }
public EditHotListDialog() {
InitializeComponent();
Domains = new ObservableCollection<ItemChoice<int?>>();
ListTypes = new ObservableCollection<ItemChoice<int?>>();
Domains .Add( new ItemChoice<int?> { Key = null, Value = "-- Pick a Domain --"} );
ListTypes.Add( new ItemChoice<int?> { Key = null, Value = "-- Pick a List Type --" } );
KeywordCache.KeywordCacheUpdated += KeywordCacheUpdated;
}
private void EditHotListDialog_Loaded( object sender, RoutedEventArgs e ) {
UpdateChoices();
DomainPicker.SelectedIndex = 0;
ListTypePicker.SelectedIndex = 0;
}
void HotList_PropertyChanged( object sender, PropertyChangedEventArgs e ) {
HotListViewModel hotList = sender as HotListViewModel;
CanSave = !( string.IsNullOrEmpty( hotList.Name ) || string.IsNullOrWhiteSpace( hotList.Name ) ) && hotList.ListTypeId > 0 && hotList.DomainId > 0;
}
private void OkButton_Click( object sender, RoutedEventArgs e ) {
if ( ValidateHotList() ) {
DialogResult = true;
Close();
}
e.Handled = true;
}
private void OnHotListChanged( HotListViewModel oldHotList, HotListViewModel newHotList ) {
if ( oldHotList != null ) {
oldHotList.PropertyChanged -= HotList_PropertyChanged;
}
if ( newHotList != null ) {
newHotList.PropertyChanged += HotList_PropertyChanged;
}
}
private static void OnHotListChanged( DependencyObject d, DependencyPropertyChangedEventArgs e ) {
EditHotListDialog dialog = d as EditHotListDialog;
dialog.OnHotListChanged( e.OldValue as HotListViewModel, e.NewValue as HotListViewModel );
}
private void UpdateChoices() {
. . .
}
private bool ValidateHotList() {
if ( string.IsNullOrEmpty( HotListNameBox.Text.Trim() ) ) {
CarSystemMessageBox.Show( "Please enter a name for the Hot List.", "Please Name the Hot List", MessageBoxButton.OK, MessageBoxImage.None );
return false;
}
if ( ListTypePicker.SelectedIndex <= 0 ) {
CarSystemMessageBox.Show( "Please select the List Type from the drop down that specifies what type of Hot List this is.", "Please Specify a List Type", MessageBoxButton.OK, MessageBoxImage.None );
return false;
}
if ( DomainPicker.SelectedIndex <= 0 ) {
CarSystemMessageBox.Show( "Please select the Domain from the drop down that this Hot List Entry belongs to.", "Please Specify a Domain", MessageBoxButton.OK, MessageBoxImage.None );
return false;
}
return true;
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChangedEvent( string propertyName ) {
if ( PropertyChanged != null ) {
PropertyChanged( this, new PropertyChangedEventArgs( propertyName ) );
}
}
#endregion
}
}
When I debug this code, I see the two ObservableCollections get populated with data. This occurs in the UpdateChoices method. I've put the call to UpdateChoices in the constructor as well as where it is in the code above.
The problem is that after the two ObservableCollections are populated, there are no Items in the ComboBoxes. When I set the SelectedIndex property to 0, nothing gets selected. When the Dialog finally opens, nothing is selected in either of the ComboBoxes.
I've used this pattern in a number of UserControls on the MainWindow of my application with success, but this is the first time I've used it in a dialog. Where is the right place to call the UpdateChoices method and to set the SelectedIndex properties of the ComboBoxes?
P.S. I didn't include the details of the UpdateChoices method because it's not pertinent to the question.

Answer 1

Your DataContext is set to HotList, which is at the same level as the properties you are trying to access. Either change the DataContext to be the whole dialog, or move the observable collections into the HotList object.

Answer 2

I don't know what the problem with the binding was, but I got rid of it and just set the ItemsSource properties of the ComboBox controls in the dialog's Loaded event handler. Everything works now.

Answer 3

Check out MVVM Pattern. Almost no Code behind is needed and you get testable code.