How to draw by VisualCollection?

Question

3.00/5 (1 vote)

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Goal: To draw shapes by VisualCollection.
Problem: It draws nothing.
Question: How to solve?
Code:

C#

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        this.Loaded += MainWindow_Loaded;
    }

    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        VisualCollection vc = new VisualCollection(this);
        DrawingVisual dv = new DrawingVisual();
        DrawingContext dc = dv.RenderOpen();

        dc.DrawRectangle(Brushes.Red, new Pen(Brushes.Red, 5), new Rect(10, 10, 100, 100));
        dc.Close();

        vc.Add(dv);
    }
}

Posted 2-Jun-15 10:08am

Ziya1995

Updated 2-Jun-15 10:12am

v2

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Comments

Sergey Alexandrovich Kryukov 2-Jun-15 16:39pm

I'm glad to see serious improvements in how you ask questions, congratulations!
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-06-02T10:53:00

The problem is that you never use your VisualCollection, only create it. How do you think the rest of your application can "know" that this collection even exist?

You don't even need this fictional "Loaded" event; you can call the code adding visuals from the constructor directly. For example, the rendering you tried to create in your code sample can be done this way:

C#

public partial class MainWindow : Window {

    public MainWindow() {
        InitializeComponent();
        visuals = new VisualCollection(this);
        DrawIt();
    } // MainWindow constructor

    VisualCollection visuals;

    void DrawIt() {
            DrawingVisual visual = new DrawingVisual();
            using (DrawingContext dc = visual.RenderOpen()) {
                dc.DrawRectangle(
                    Brushes.Red, new Pen(Brushes.Red, 5),
                    new Rect(10, 10, 100, 100));
            }
            visuals.Add(visual);
    } //DrawIt

    protected override Visual GetVisualChild(int index) {
        return visuals[index];
    } //GetVisualChild
    protected override int VisualChildrenCount {
        get { return visuals.Count; }
    } //VisualChildrenCount

} // MainWindow class

Can you spot the difference? :-)

But I would not advise drawing on the Window directly. Instead, create some custom UIElement (derived class) using the visuals in exact same way, and add it the the window's logical tree, as any other UIElement (to a grid or other container, or a window itself), directly or using XAML. Please see the complete sample in this tutorial:
https://tarundotnet.wordpress.com/2011/05/19/wpf-tutorial-drawing-visual[^].

I tried it out, it works.

—SA