WPF Canvas, how to add children dynamically with MVVM code behind

Question

Requirement:

To draw one Bitmap Image and rectangle(s) based on the collection of points. The rectangle should exactly fit on the pixels location over the image. There is also some text need to be added inside the rectangle.

The Image will be always only one and the rectangles will be dynamically added.

Current Solution:

Have a canvas with Image Control. Add the the dynamic code under the code behind file ViewImageResult.xaml.cs.

    private void DrawResult(int left, int right, int width, int height)
    {
        Border bord = new Border();
        bord.BorderThickness = new Thickness(1);
        bord.BorderBrush = Brushes.Red;
        bord.Width = width;
        bord.Height = height;
        _mainCanvas.Children.Add(bord);
        Canvas.SetLeft(bord, left);
        Canvas.SetTop(bord, right);
    }

Issue:

Since i follow MVVM pattern, the collection of points for rectangle is in my ViewModel file ViewImageResultModel.cs. I am not able to add the child rectangle dynamically from the ViewModel file.

score 53 · Accepted Answer · edited Sep 27 '11 at 15:24

ItemsControl is your friend:

<Grid>
    <Image Source="..."/>
    <ItemsControl ItemsSource="{Binding Points}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <Canvas/>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemContainerStyle>
            <Style>
                <Setter Property="Canvas.Left" Value="{Binding X}"/>
                <Setter Property="Canvas.Top" Value="{Binding Y}"/>
            </Style>
        </ItemsControl.ItemContainerStyle>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Border BorderBrush="Red" BorderThickness="1" Width="{Binding Width}" Height="{Binding Height}"/>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Grid>

The above assumes your VM exposes a collection of points via a Points property, and that each point VM has X, Y, Width, and Height properties.

Many Thanks Kent. That works fabulous with small change – Sathya Ram Jun 13 '11 at 10:30 — Sathya Ram, Jun 13 '11 at 10:30
That... that is just beautiful. – gwiazdorrr Feb 28 '12 at 08:54 — gwiazdorrr, Feb 28 '12 at 08:54

score 2 · Answer 2 · edited Mar 26 '16 at 22:20

Added IsItemsHost="True" to the Canvas of Kent's solution:

<Grid>
    <Image Source="..."/>
    <ItemsControl ItemsSource="{Binding Points}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <Canvas  IsItemsHost="True"/>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemContainerStyle>
            <Style>
                <Setter Property="Canvas.Left" Value="{Binding X}"/>
                <Setter Property="Canvas.Top" Value="{Binding Y}"/>
            </Style>
        </ItemsControl.ItemContainerStyle>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Border BorderBrush="Red" BorderThickness="1" Width="{Binding Width}" Height="{Binding Height}"/>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Grid>

The nice think about typing versus talking is that when you realize your mistake you don't have to hit "Add Comment"... — Joris Weimar, Jan 11 '13 at 21:46

WPF Canvas, how to add children dynamically with MVVM code behind

Requirement:

Current Solution:

Issue:

2 Answers2

Linked