Bryan's Coding Corner

I’ve created a new project for Behaviors on CodePlex, the WPF Behavior Library. A behavior is basically just a set of attached properties and functionality you can attach to a visual element. By attaching the behavior to the bit of UI you give it the additional functionality.

The first behavior I’ve included is Drag & Drop. There are a few drag and drop behaviors out there right now but they all require a lot of modification to use in other applications. Most of them only work for a subset of the UI elements that inherit from ItemsControl (mostly the ones that have their own ItemsContainers), some can’t move items between windows, and some don’t allow you to change logic behind moving items. In short none were general purpose enough to just grab a dll and use the behavior.

So take a look at the WPF Behavior Library, give feedback, report bugs, suggest new behaviors and features, or contribute.

WPF WPF, wpfbehaviorlibrary

You know how sometimes you run into problems that you know should be really simple but you just can’t manage to solve them? Well one of those problems for me was making a grid an ItemsHost and actually having it work. Sure you can always set IsItemsHost=”True” but you’ll just end up with every item in your ItemsSource all stacked on top of each other. A few weeks ago I ran into this same problem again and couldn’t find a way around it. So after beating my head against the wall for a few hours I finally gave up and posted on StackOverflow, within a half hour I had the answer I’d been trying to figure out for the better part of a day.

It turns out that setting IsItemsHost to True on a panel creates the required ContentPresenters and nothing you can do will let you get at them directly (believe me, I tried). The solution is to create a keyless style that targets ContentPresenter and let this style take care of the dirty work.

Without furthur ado, here’s an example.

The Data

Class DataPoint
	Private myRow As Integer
	Public Property Row() As Integer
		Get
			Return myRow
		End Get
		Set(ByVal value As Integer)
			myRow = value
		End Set
	End Property

	Private myCol As Integer
	Public Property Col() As Integer
		Get
			Return myCol
		End Get
		Set(ByVal value As Integer)
			myCol = value
		End Set
	End Property

	Private myText As String
	Public ReadOnly Property Text() As String
		Get
			Return myText
		End Get
	End Property

	Public Sub New(ByVal x As Integer, ByVal y As Integer)
		Me.Row = y
		Me.Col = x
		myText = "Column " + x.ToString + ", Row " + y.ToString
	End Sub
End Class

Load the test data and set it as the data context for the window

Class GridAsItemsHostExample
	Private myTestData As TestData

	Public Sub New()
		InitializeComponent()

		myTestData = New TestData()
		Me.DataContext = myTestData
	End Sub
End Class

Class TestData
	Private myDataSet As List(Of DataPoint)
	Public Property DataSet() As List(Of DataPoint)
		Get
			Return myDataSet
		End Get
		Set(ByVal value As List(Of DataPoint))
			myDataSet = value
		End Set
	End Property

	Public Sub New()
		Me.DataSet = New List(Of DataPoint)
		For x As Integer = 0 To 1
			For y As Integer = 0 To 1
				Me.DataSet.Add(New DataPoint(x, y))
			Next
		Next
	End Sub
End Class

And finally the window, note the ContentPresenter style.

<Window x:Class="GridAsItemsHostExample"
		xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
		xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
		Title="Grid As ItemsHost Example"
		SizeToContent="WidthAndHeight">

	<ItemsControl ItemsSource="{Binding DataSet}">
		<ItemsControl.ItemContainerStyle>
			<Style TargetType="ContentPresenter">
				<Setter Property="Grid.Column"	Value="{Binding Col}"	/>
				<Setter Property="Grid.Row"		Value="{Binding Row}"	/>
				<Setter Property="Margin"		Value="5"				/>
			</Style>
		</ItemsControl.ItemContainerStyle>
		<ItemsControl.ItemTemplate>
			<DataTemplate>
				<TextBlock Text="{Binding Text}"   />
			</DataTemplate>
		</ItemsControl.ItemTemplate>
		<ItemsControl.Style>
			<Style TargetType="{x:Type ItemsControl}">
				<Setter Property="Template">
					<Setter.Value>
						<ControlTemplate TargetType="{x:Type ItemsControl}">
							<Grid HorizontalAlignment="Stretch"
								  IsItemsHost="True"
								  ShowGridLines="True">
								<Grid.ColumnDefinitions>
									<ColumnDefinition />
									<ColumnDefinition />
								</Grid.ColumnDefinitions>
								<Grid.RowDefinitions>
									<RowDefinition />
									<RowDefinition />
								</Grid.RowDefinitions>
							</Grid>
						</ControlTemplate>
					</Setter.Value>
				</Setter>
			</Style>
		</ItemsControl.Style>
	</ItemsControl>
</Window>

Code Samples Grid, ItemsHost, WPF, xaml