Sorry that the title is a bit vague but I could'n come up with a better one.
For arguments sake let's say I'm developing a simple drawing application, where the user just clicks and drags to draw a line (I'm not really developing that, but just to keep it simple).
I have a custom shape for the line to draw. Now I want to add new lines to the view as needed, but I'd like to use an ObservableCollection property via data binding on the view model to do that. Usaully I would use an ItemsControl. But of course the ItemsControl automatically positions it's items, which is not what I want.
Does anyone have an idea how to do that? Is there a way to disable the layout functions of an ItemsControl?
You can change the ItemsPanelTemplate of an ItemsControl so it uses a Canvas instead of a StackPanel to hold its items, then use the ItemContainerStyle to bind the Canvas.Top and Canvas.Left properties to your data object to position them.
<ItemsControl ItemsSource="{Binding MyCollection}">
<!-- ItemsPanelTemplate -->
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<!-- ItemContainerStyle -->
<ItemsControl.ItemContainerStyle>
<Style>
<Setter Property="Canvas.Top" Value="{Binding Y}" />
<Setter Property="Canvas.Left" Value="{Binding X}" />
</Style>
</ItemsControl.ItemContainerStyle>
</ItemsControl>
I have a blog article about the ItemsControl that explains in more detail how an ItemsControl works if you're interested.
Related
Why isn't my ItemsControl creating a ContentPresenter for each item? I'm guessing this is what's making my items not show up (they're set to visible and in the right spot when I inspect using the Live Visual Tree). I'm basically reusing code that works up above in a different ItemsControl and I haven't been able to find anything while searching Google/Stackoverflow with this issue. I can include view model code but I don't think it's related because I see the appropriate values in the Live Property Explorer and can see each WellContainer is in it's appropriate grid cell.
XAML:
<ItemsControl
Grid.Row="1"
Grid.Column="1"
ItemsSource="{Binding Wells}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Grid
x:Name="m_WellGrid"
Margin="5"
wpf:GridHelpers.RowCount="{Binding RowCount}"
wpf:GridHelpers.ColumnCount="{Binding ColumnCount}">
</Grid>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemContainerStyle>
<Style>
<Setter
Property="Grid.Row"
Value="{Binding Path=WellRow}"/>
<Setter
Property="Grid.Column"
Value="{Binding Path=WellCol}"/>
</Style>
</ItemsControl.ItemContainerStyle>
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock
Text="A"
Margin="4"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Live Visual Tree Inspection:
The ItemsControl is designed to wrap the items in a container only when necessary, that is, when the item is not eligible to be its own container. From your comment we find that WellContainer derives from Control, thus is eligible to be its own container1 and is not wrapped in a ContentPresenter. Unfortunately there's no way to control this behavior directly, but you could subclass ItemsControl and override the ItemsControl.IsItemItsOwnContainerOverride method to modify the default behavior.
1 As we can see in the ItemsControl source code it is enough for the item to be of UIElement type to be eligible to be its own container.
I have a big size Canvas and a lot of small user controls placed over it. At a time only a small portion of the canvas is visible on screen. The usercontrols are created by the ItemsControl which is Data bound to a ViewModel.
<Canvas Height="10000" Width="10000" Background="White" >
<ItemsControl ItemsSource="{Binding Path=MyData}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Views:MyControl />
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemContainerStyle>
<Style TargetType="ContentPresenter">
<Setter Property="Canvas.Left" Value="{Binding Left}"/>
<Setter Property="Canvas.Top" Value="{Binding Top}"/>
</Style>
</ItemsControl.ItemContainerStyle>
</ItemsControl>
</Canvas>
Now since the number of usercontrols is huge, it takes a lot of time to load the whole canvas. I want to load only those controls which are in the visible frame currently. If I move the canvas, the usercontrols under the new visible area should be loaded. The prime reason I want to do this is because of performance lag associated with loading large number of usercontrols. I want to do it in Canvas what VirtualizingStackPanel does to StackPanel.
Is there a way to do it?
Thanks for the help
First, test loading blank user controls. That is user controls that display nothing at all. If this is fast enough it tells us that the problem is not in the canvas handling the large number of user controls but in initialising the user controls.
So, if that is the case, create a simple place holder user control that on IsVisibleChanged event firing loads the target user control using itself as the canvas.
All depends on the first test.
Look into virtualization. Instead of using Canvas, use a ListBox with your own implementation of VirtualizingPanel, that can act just as a Canvas and will only create the controls that are supposed to be visible.
There are many great resources on UI virtualization, here are two quick picks:
UI Virtualization in WPF by kirupa
Implementing a virtualized panel in WPF (Avalon) by Dan Crevier
I've started developing my code using the example from SO WPF: arranging collection items in a grid. Now, to gain cell selection capability, I renamed each ItemsControl to ListBox, because a ListBox is-a ItemsControl (XAMl somewhat simplified):
<ListBox HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" ItemsSource="{Binding YourItems}">
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<Grid/>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemContainerStyle>
<Style>
<Setter Property="Grid.Column" Value="{Binding X}"/>
<Setter Property="Grid.Row" Value="{Binding Y}"/>
</Style>
</ListBox.ItemContainerStyle>
<ListBox.ItemTemplate>
<DataTemplate>
<Image RenderOptions.BitmapScalingMode="LowQuality" Source="{Binding ...ImageSource, Mode=OneWay}">
</Image>
</DataTemplate>
</ListBox.ItemTemplate>
The grid is filled with glyph run test imaged, based on the code here.
Surprisingly it worked - kind of. Selection works. However, in the case of the ItemsControl, there was no scroll bar. Everything scaled nicely. When I made the window smaller, the grid cells shrunk and so did the images. When I made the window larger, everything scaled up.
Now, with the ListBox that's not the case. The images size stays fixed. If the window isn't large enough, there's an horizontal scroll bar and when the window isn't large enough, some of the images are hidden and the user needs to scroll to the right.
So, my question is: If a ListBox is-an ItemControl, why don't my images scale the same? What should I do to correct it?
This is because ListBox and ItemsControl use different styles. You might easily apply the ItemControl's default style to your ListBox:
<ListBox Style="{StaticResource ResourceKey={x:Type ItemsControl}}">
I'm trying to implement a diagram with movable/resizeable parts in WPF.
I would like to use ItemsControl with ItemsPanel configured to be "DynamicCanvas".
All you need to know about DynamicCanvas right now is that it acts like a usual canvas - with one exception - it utilizes attached properties to store information about X,Y attributes on its children.
My code:
<ItemsControl IsTabStop="False" ItemsSource="{Binding ElementName=comboBox1,Path=SelectedItem.Source.Table}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<s:TableControl Table="{Binding}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemContainerStyle>
<Style>
</Style>
</ItemsControl.ItemContainerStyle>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<!--<ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto">-->
<c:DynamicCanvas SizeHeightToContent="True" SizeWidthToContent="True" ClipToBounds="True" SnapsToDevicePixels="True" PreviewMouseDown="Canvas_MouseDown" IsHitTestVisible="True" Background="Gray" >
</c:DynamicCanvas>
<!--</ScrollViewer>-->
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
The controls that are being displayed on DynamicCanvas are of my custom type (below only the most important part):
<ContentControl x:Class="SubiektCommerceSynchro.ViewModel.TableControl"
c:DynamicCanvas.Left="{Binding X,Mode=TwoWay}"
c:DynamicCanvas.Top="{Binding Y,Mode=TwoWay}"
Width="450" Height="300"
></ContentControl>
Now the problem and the question:
The part here that doesn't work is with attached properties c:DynamicCanvas.Left(Top).
Lets put it in steps:
1) DynamicCanvas expects its immediate children to have c:DynamicCanvas.Left and c:DynamicCanvas.Top defined
2) ItemsPanel when putting TableControls onto the DynamicCanvas wraps them in some kind of container
3) DynamicCanvas sees no attached properties on its immediate children => treats them as being positioned at (0,0) and renders them effectively unmoveable.
How can I resolve this issue?
Does this help?
<ItemsControl.ItemContainerStyle>
<Style>
<Setter Property="c:DynamicCanvas.Left"
Value="{Binding X,Mode=TwoWay}"/>
<Setter Property="c:DynamicCanvas.Top"
Value="{Binding Y,Mode=TwoWay}"/>
</Style>
</ItemsControl.ItemContainerStyle>
You have to modify the ControlTemplate of the item wrapper in the ItemContainerStyle. If you set it to simple ContentPresenter, the items will not be wrapped in anything (the contents of the DataTemplate will be pasted directly into the DynamicCanvas).
See this article.
I want to add a dynamic number of ellipses to a canvas and set the ellipse position (canvas.top, canvas.left). I tried binding to an ItemsControl but it each item (ellipse) has a container, so I cant set the ellipses position directly. I don't want an items container, I just want a canvas that contains ellipses.
Can this be done?
Try this - worked for me -- I use it to freely place textblocks on a canvas.
Re: Re: Positioning Items when Canvas is the ItemsPanel of an ItemsControl
02-26-2010 7:17 AM |
There is an alternative simpler solution that does work in silverlight 3.
<Canvas>
<ItemsControl ItemsSource={Binding MyItems}>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Canvas>
<TextBlock Canvas.Left={Binding Left} Canvas.Top={Binding Top} Text={Binding Text} />
</Canvas>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Canvas>
If the MyItems is a list of items that are of a class that has Left, Top and Text public properties, this works fine. I have also tested with Line and Border to draw simple bar graph graphics in silverlight 3.
From the bottom of this post:
http://forums.silverlight.net/forums/p/29753/450510.aspx#450510
Combine it with a Silverlight DataTemplateSelector and you can change the objects you draw based on view model properties:
http://www.codeproject.com/KB/silverlight/SLTemplateSelector.aspx
Ordinarily I would say use an ItemsControl in conjunction with a Canvas:
<ItemsControl ItemsSource="{Binding Ellipses}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemsContainerStyle>
<Style>
<Setter Property="Canvas.Left" Value="{Binding Left}"/>
<Setter Property="Canvas.Top" Value="{Binding Top}"/>
</Style>
</ItemsControl.ItemsContainerStyle>
</ItemsControl>
But in a display of Silverlight suckiness, the ItemContainerStyle property does not work on ItemsControl. It has support in ItemsControl, but it's not exposed by ItemsControl itself. Instead, it's up to subclasses of ItemsControl - such as ListBox - to expose it. Oh, and those subclasses have to be provided by Microsoft because the functionality is protected internal, so you can't just subclass ItemsControl and expose this stuff yourself. :S
So you could use ListBox instead, possibly by subclassing it and changing its item container to something simpler than a ListBoxItem. Or you could just use ListBox directly and fiddle around until the ListBoxItems look the way you want them to (i.e. not selected).