WPF/Silverlight Bind Canvas to Collection of View Model Elements - wpf

Question

Is it possible to use a DataTemplate to render a collection of points as a bunch of lines (with data binding and drag and drop)?
Here are the details:
I have multiple objects in my view model. These objects ultimately have locations on a canvas specified in absolute pixel coordinates. I need to be able to drag and drop these items around on the canvas and update their coordinates. Some objects are represented by a point, others are a collection of line segments. I'm using MVVM (Jounce). Should my view model expose a ObservableCollection<Shape> that somehow binds the coordinates? That feels wrong. Or is there a way I can use DataTemplates here to draw lines with points on the end of each line segment given a collection of line segments? Here is an example ViewModel:
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Jounce.Core.ViewModel;
namespace CanvasBindTest.ViewModels
{
/// <summary>
/// Sample view model showing design-time resolution of data
/// </summary>
[ExportAsViewModel(typeof(MainViewModel))]
public class MainViewModel : BaseViewModel
{
public MainViewModel()
{
var start = new PointView { X = 0, Y = 0 };
var middle = new PointView { X = 1132 / 2, Y = 747 / 2 };
var end = new PointView() { X = 1132, Y = 747 };
var lineView = new LineView(new[] { start, middle, end });
Lines = new LinesView(new[] { lineView });
}
public LinesView Lines { get; private set; }
}
public class LinesView : BaseViewModel
{
public ObservableCollection<LineView> Lines { get; private set; }
public LinesView(IEnumerable<LineView> lines)
{
Lines = new ObservableCollection<LineView>(lines);
}
}
public class LineView : BaseViewModel
{
public ObservableCollection<PointView> Points { get; private set; }
public LineView(IEnumerable<PointView> points)
{
Points = new ObservableCollection<PointView>(points);
}
}
public class PointView : BaseViewModel
{
private int x, y;
public int X
{
get { return x; }
set { x = value; RaisePropertyChanged(() => X); }
}
public int Y {
get { return y; }
set { y = value; RaisePropertyChanged(() => Y); }
}
}
}
Here is the View, which is a canvas wrapped in a ItemsControl with a background image. The view model coordinates are relative to the background image's unscaled size:
<UserControl x:Class="CanvasBindTest.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:viewModels="clr-namespace:CanvasBindTest.ViewModels"
mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="400">
<UserControl.Resources>
<DataTemplate x:Key="SkylineTemplate" DataType="viewModels:LineView">
<ItemsControl ItemsSource="{Binding Points}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<!--I have a collection of points here, how can I draw all the lines I need and keep the end-points of each line editable?-->
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</DataTemplate>
</UserControl.Resources>
<Grid d:DataContext="{d:DesignInstance viewModels:MainViewModel, IsDesignTimeCreatable=True}">
<ScrollViewer x:Name="Scroll">
<ItemsControl ItemsSource="{Binding Lines}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas>
<Canvas.Background>
<ImageBrush Stretch="Uniform" ImageSource="Properties/dv629047.jpg"/>
</Canvas.Background>
</Canvas>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</ScrollViewer>
</Grid>
</UserControl>

Answer 1

Your LineView must be LineViewModel, it'll be more correct.
I describe the mechanism for points, for lines I think you will understand by yourself.
Main Control
Use ItemsControl.
ItemsControl.PanelControl must be Canvas.
ItemsSource - Your collection of PointWiewModel.
Make two DataTemplates for types PointWiewModel.
Make the PointView control and put it into the appropriate DataTemplate.
PointView control
Two way bind Canvas.X attached property to PointViewModel.X property.
Two way bind Canvas.Y attached property to PointViewModel.Y property.
Add logic of changing Canvas.X and Canvas.Y when you drag a PointView control.
Result
After that you could drag your (for example) PointVew control and the properties in your view model will be updated because of two way binding.
Suppose I understand correctly what do you want.
Added answers to the questions
Silverlight 5 supports it. That's mean all the items will be placed on the Canvas control. Some article about ItemsControl.
<ItemsControl>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas></Canvas>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
PointView is the second user control.
Note: I've described a way to draw an array of points with MVVM. You can drag each point on the canvas and receiving the new coordinates in your view model. (Maybe my description was a bit confusing on this stage so I've deleted LineViews from it)
In order to make a Lines, you have to connect your points. It'll be more difficult so I suggest you to make a variant with points only.
When you will be familiar with it, you can move your ItemsControl into templated control. Make your own ItemSource collection and drawing the Path by this points when they will change the position.
You can also search some opensource graph controls and see how they drawing curving lines by dots. Actually they usually do doing it with the Path like I have described.
Sorry, but I wouldn't write more because it'll became an article but not an answer)
P.S: It is interesting question, so If I have some free time I may be write an article. About templated controls you can read here.

Answer 2

It's absolutely disgusting how much XAML this takes. I'll look for a way to clean it up using styles and templates. Also, I need to draw the line to the center of the point, that shouldn't be hard. For now, below is what worked. I ended up created a Collection<Pair<Point, Point>> ViewModel to bind the "Line" collection. Otherwise I'm looking at the line point-by-point and can't draw a line since I can't find X2/Y2.
Thanks for the inspiration Alexander.
Here is the XAML:
<ItemsControl ItemsSource="{Binding Lines}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate DataType="viewModels:LineViewModel">
<ItemsControl ItemsSource="{Binding LineSegments}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<ItemsControl>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl ItemsSource="{Binding Lines}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Line X1="{Binding Item1.X}" X2="{Binding Item2.X}" Y1="{Binding Item1.Y}" Y2="{Binding Item2.Y}" Stroke="Black" StrokeThickness="2"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<ItemsControl ItemsSource="{Binding LineSegment}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Ellipse Canvas.Left="{Binding X}" Canvas.Top="{Binding Y}" Width="10" Height="10" Fill="Black">
<Ellipse.RenderTransform>
<TranslateTransform X="{Binding X}" Y="{Binding Y}"/>
</Ellipse.RenderTransform>
</Ellipse>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ItemsControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Here is the ViewModel:
namespace CanvasBindTest.ViewModels
{
/// <summary>
/// Sample view model showing design-time resolution of data
/// </summary>
[ExportAsViewModel(typeof (MainViewModel))]
public class MainViewModel : BaseViewModel
{
public MainViewModel()
{
var start = new PointViewModel {X = 0, Y = 0};
var middle = new PointViewModel {X = 30, Y = 10};
var end = new PointViewModel {X = 20, Y = 0};
var simpleLine = new LineSegmentsViewModel(new[] {start, middle, end});
Lines = new ObservableCollection<LineViewModel> {new LineViewModel(new[] {simpleLine})};
}
public ObservableCollection<LineViewModel> Lines { get; private set; }
}
public class LineViewModel : BaseViewModel
{
public LineViewModel(IEnumerable<LineSegmentsViewModel> lineSegments)
{
LineSegments = new ObservableCollection<LineSegmentsViewModel>(lineSegments);
}
public ObservableCollection<LineSegmentsViewModel> LineSegments { get; private set; }
}
public class LineSegmentsViewModel : BaseViewModel
{
public LineSegmentsViewModel(IEnumerable<PointViewModel> lineSegment)
{
LineSegment = new ObservableCollection<PointViewModel>(lineSegment);
Lines = new Collection<Tuple<PointViewModel, PointViewModel>>();
var tmp = lineSegment.ToArray();
for (var i = 0; i < tmp.Length - 1; i++)
{
Lines.Add(new Tuple<PointViewModel, PointViewModel>(tmp[i], tmp[i+1]));
}
}
public Collection<Tuple<PointViewModel, PointViewModel>> Lines { get; private set; }
public ObservableCollection<PointViewModel> LineSegment { get; private set; }
}
public class PointViewModel : BaseViewModel
{
private int x, y;
public int X
{
get { return x; }
set
{
x = value;
RaisePropertyChanged(() => X);
}
}
public int Y
{
get { return y; }
set
{
y = value;
RaisePropertyChanged(() => Y);
}
}
}
}