WPF

WPF: Transform trigger into event

Nat Luengnaruemitchai — Thu, 20 Sep 2007 12:55:38 GMT

Yesterday, I had a problem where I need to hook up an event to a certain data condition. I first thought about EventTrigger. However, it does the other way around. This class is responsible for convert event into trigger. So I digged around WPF architecture to see what I can do and bingo. I found that I can create an attached property with the following construct

and then in XAML, you can register for this event by

public static readonly DependencyProperty SomethingHappenedProperty = DependencyProperty.RegisterAttached("SomethingHappened",typeof(bool),typeof(Window1),new PropertyMetadata(false,new PropertyChangedCallback(SomethingHappened)));public bool GetSomethingHappened(DependencyObject d)
{
    return (bool)d.GetValue(SomethingHappenedProperty);
}public void SetSomethingHappened(DependencyObject d, bool value)
{
    d.SetValue(SomethingHappenedProperty, value);
}private void SomethingHappened(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    // do something here
}

Free WPF DataGrid from Infragistics

Nat Luengnaruemitchai — Wed, 19 Sep 2007 02:25:59 GMT

Andrew Flick announced that Infragistics WPF Express Edition will be free as well. Before this release, xamDataGrid suffered a lot of performance problem. It seems that they have fixed various performance problem. So I think I will give it a try again later. To try it out visit http://blogs.infragistics.com/blogs/andrew_flick/archive/2007/09/13/infragistics-netadvantage-for-wpf-express-aka-free-grid.aspx for more information.

WPF ComboBox with LimitToList feature: Part I

Nat Luengnaruemitchai — Wed, 08 Aug 2007 01:37:47 GMT

Sometimes, you would like to get a combobox where a user can type. This can be done by turning on IsEditable property to true. However, it opens another can of worm, it means the user can type anything in the combobox even text that is not in the ItemsSource.

To provide LimitToList feature, you can hook up an event to PreviewLostKeyboardFocus as follows:

private void ComboBox_PreviewLostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)

{

if (!e.Handled)

{

TextBox textBox = e.OldFocus as TextBox;

ComboBox comboBox = sender as ComboBox;

if (textBox != null && comboBox!=null)

{

DependencyObject common = comboBox.FindCommonVisualAncestor(e.NewFocus as DependencyObject);

// validate only the case when user step out of this control

if (common != comboBox)

{

bool invalid = !string.IsNullOrEmpty(textBox.Text) && comboBox.SelectedIndex < 0;

if (invalid)

{

e.Handled = true;

}

Later, I will show you how to create a visual clue to indicate that the combobox is invalid

WPF Nested Template Bug

Nat Luengnaruemitchai — Sun, 29 Jul 2007 13:17:54 GMT

I posted in MSDN Forum a while ago that I ran into a WPF bug that occurs when you put one template inside another template like

The above code won't fail during the compilation. However,during the run, you will notice that only the first item of the outer listbox will show up but not the rest. Sam Bent, WPF/WinFX Dev Lead answered that this is a nested template bug. If template is used nestedly, the result will be unexpected. To workaround, the template should be defined as a separated template in Resources section like:

<Window.Resources>
    <DataTemplate x:Key="InnerTemplate">
        <StackPanel>
            <ComboBox ItemsSource="{Binding Source={StaticResource CategoryData}, XPath=Category}"
            SelectedValue="{Binding XPath=Category}"/>
            <TextBlock Text="{Binding XPath=Title}" />
            <TextBlock Text="{Binding XPath=Summary}" />
        </StackPanel>
    </DataTemplate>
    <DataTemplate x:Key="OuterTemplate">
        <StackPanel>
            <ListBox HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch" HorizontalAlignment="Stretch"
                ItemTemplate="{StaticResource InnerTemplate}" Background="Honeydew" ItemsSource="{Binding XPath=.}">
            </ListBox>
        </StackPanel>
    </DataTemplate>
</Window.Resources>

<Grid VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
    <ListBox HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch" HorizontalAlignment="Stretch"
            ItemTemplate="{StaticResource OuterTemplate}" Background="Honeydew">
        <ListBox.ItemsSource>
            <Binding Source="{StaticResource InventoryData}"
                    XPath="*[@Stock='out'] | *[@Number>=8 or @Number=3]"/>
        </ListBox.ItemsSource>
    </ListBox>
</Grid>