Question

hi I have a C# app that features a canvas. I’d like to programmatically place a textbox (with text) on it. I’ve tried and tried but all I get is a fully transparent rectangle where my textbox ought to be. is it me or is this a known difficulty?

UPDATE:
I should have mentioned.. (Sorry!) I’m also overriding OnRender in the object to be drawn like so:

    protected override void OnRender(DrawingContext drawingContext)
    {
        drawingContext.PushTransform(TransformRotation);
        Draw(drawingContext);
        drawingContext.Pop();
    }

and Draw is implemented like so:

    public override void Draw(DrawingContext drawingContext)
    {
        Rect graphicRectangle = Rectangle;
        ITransform2d transformToDisplay = Layer.TransformToDisplay;
        if (transformToDisplay != null)
        {
            graphicRectangle = new Rect(transformToDisplay.Transform(Rectangle.TopLeft),
                                        transformToDisplay.Transform(Rectangle.BottomRight));
        }
        textBox.Height = graphicRectangle.Height;
        textBox.Width = graphicRectangle.Width;
        Canvas.SetLeft(textBox, graphicRectangle.Left);
        Canvas.SetTop(textBox, graphicRectangle.Top);
    }

Answer 1

Canvas being a panel whose purpose is to arrange and display some kind of content i would recommend that you do not do anything like this.

If you need a Canvas with a TextBox use composition, for example create a UserControl with a TextBox over or under the Canvas and expose relevant properties and methods on the UserControl’s interface.

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Use Panel elements to position and arrange child objects in Windows Presentation Foundation (WPF) applications. – MSDN