WPF: Placing a textbox randomly on a canvas - wpf

Question

I have a canvas of sorts derived from a 'Panel' used for custom drawing of lines and other geometries, all from VB code. I got this approach from a book and I'm not sure it's the best approach. The drawing part works so far for me.
But what I need is to put a textbox control on the control containing text which can be edited by the user. The textbox needs to be placed at coordinates determined dynamically and later deleted. There will probably be other controls handled so.
The following code does nothing:
tb = New TextBox()
tb.Text = "How now brown cow?"
tb.BorderThickness = New Thickness(3)
tb.BorderBrush = Brushes.CadetBlue
drawingSurface.Children.Add(tb)
This is the definition of my DrawingCanvas:
Public Class DrawingCanvas
Inherits Panel
Private visuals As New List(Of Visual)()
Private hits As New List(Of DrawingVisual)()
Protected Overrides Function GetVisualChild(ByVal index As Integer) As Visual
Return visuals(index)
End Function
Protected Overrides ReadOnly Property VisualChildrenCount() As Integer
Get
Return visuals.Count
End Get
End Property
Public Sub AddVisual(ByVal visual As Visual)
visuals.Add(visual)
MyBase.AddVisualChild(visual)
MyBase.AddLogicalChild(visual)
End Sub
Public Sub DeleteVisual(ByVal visual As Visual)
visuals.Remove(visual)
MyBase.RemoveVisualChild(visual)
MyBase.RemoveLogicalChild(visual)
End Sub
Public Function GetVisual(ByVal point As Point) As DrawingVisual
Dim hitResult As HitTestResult = VisualTreeHelper.HitTest(Me, point)
Return TryCast(hitResult.VisualHit, DrawingVisual)
End Function
Public Function GetVisuals(ByVal region As Geometry) As List(Of DrawingVisual)
hits.Clear()
Dim parameters As New GeometryHitTestParameters(region)
Dim callback As New HitTestResultCallback(AddressOf Me.HitTestCallback)
VisualTreeHelper.HitTest(Me, Nothing, callback, parameters)
Return hits
End Function
Private Function HitTestCallback(ByVal result As HitTestResult) As HitTestResultBehavior
Dim geometryResult As GeometryHitTestResult = CType(result, GeometryHitTestResult)
Dim visual As DrawingVisual = TryCast(result.VisualHit, DrawingVisual)
If visual IsNot Nothing AndAlso geometryResult.IntersectionDetail = IntersectionDetail.FullyInside Then
hits.Add(visual)
MsgBox("Ouch")
End If
Return HitTestResultBehavior.Continue
End Function
End Class
Here is the XAML. I added a textbox to the DrawingCanvas just to see if something appears. Nothing did. In fact, I want to do this in code, not XAML. I thought I could hide or move it around dynamically.
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Music"
Title="MainWindow" Height="539" Width="892">
<DockPanel>
<Menu DockPanel.Dock="Top" Name="MainMenu" VerticalAlignment="Top" Height="25">
<MenuItem Name="File" Header="File">
<MenuItem Name="Open" Header="Bla bla..."/>
</MenuItem>
</Menu>
<local:DrawingCanvas DockPanel.Dock="Bottom" x:Name="drawingSurface" RenderTransformOrigin="0.5,0.5" >
<TextBox Height="0" Name="TextBox1" Width="45" Text="How now brown cow?" />
</local:DrawingCanvas>
</DockPanel>
</Window>
Thanks for helping a nooby. A solution would be very useful for me. This was easy with windows forms, but I need the drawing speed of WPF.

Answer 1

I think you are a bit off here. In WPF you have a control called Canvas. I would suggest you use that instead of your own "DrawingCanvas", which I can't get to work btw. :( (For some reason I cant create code blocks so if someone can edit it I would be pleased)
Anyhow,
<local:DrawingCanvas DockPanel.Dock="Bottom" x:Name="drawingSurface" RenderTransformOrigin="0.5,0.5" >
<TextBox Height="0" Name="TextBox1" Width="45" Text="How now brown cow?" />
</local:DrawingCanvas>
Turns into:
<Canvas x:Name="drawingSurface">
</Canvas>
And then to add a textbox just do as your current code:
Dim tb as New TextBox
drawingSurface.Children.Add(tb)
This should give you what you need.
Heres the code for adding a rectangle to your canvas.
Private Sub DrawBackground()
Dim Rect As New Rectangle()
Rect.Height = 50
Rect.Width = 50
Rect.Fill = Brushes.Cornsilk
drawingSurface.SetTop(Rect, 30)
drawingSurface.SetLeft(Rect, 100)
drawingSurface.Children.Add(Rect)
End Sub

Answer 2

I'll add another answer that might be more in the line of what you are looking for. This is a class that inherits from Canvas that will allow you to draw stuff in the same way as say you do in your comment.
I also creates a textbox on a random location when it is created.
Public Class DrawingCanvas
Inherits Canvas
Public RandomTextBox As New TextBox
Protected Overrides Sub OnRender(dc As System.Windows.Media.DrawingContext)
Dim brush As Brush = Brushes.Black
Dim drawingPen As Pen = New Pen(Brushes.Green, 3)
dc.DrawRectangle(brush, drawingPen, New Rect(5, 5, Me.ActualWidth - 5, Me.ActualHeight - 5))
RandomTextBox.Text = "Herpdiderp"
If Not Me.Children.Contains(RandomTextBox) Then
Dim r As New Random()
RandomTextBox.Height = 23
RandomTextBox.Width = 100
Me.SetTop(RandomTextBox, r.Next(0, Me.ActualHeight - RandomTextBox.Height))
Me.SetLeft(RandomTextBox, r.Next(0, Me.ActualWidth - RandomTextBox.Width))
Me.Children.Add(RandomTextBox)
End If
End Sub
End Class

Answer 3

This is not a full answer. #WozzeC, you were right about using the canvas - almost.
I have managed to solve this in xaml alone - I want to eventually solve it in vb.net.
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<DockPanel HorizontalAlignment="Stretch" Name="DockPanel1" VerticalAlignment="Stretch" >
<Menu Height="23" DockPanel.Dock="Top" Name="Menu1" VerticalAlignment="Top" />
<Canvas Name="Canvas1" Background="Aquamarine">
<TextBox Canvas.Left="118" HorizontalScrollBarVisibility="Disabled" Canvas.Top="81" AcceptsReturn="True" Height="auto" Name="TextBox1" Width="68" Text="Herpdiderp" BorderThickness="0" Background="Aquamarine" />
</Canvas>
</DockPanel>
</Grid>
And here is a piece of code that expands the text as needed. I think it's almost totally cool. It expands both to the right and downwards, as if you're actually typing on the form. It adds a little too much on the right, but it's not visible in this version because the background color is the same.
Here is the event code that expands it to the right.
Imports System.Globalization
Class MainWindow
Private Sub TextBox1_TextChanged(sender As System.Object, e As System.Windows.Controls.TextChangedEventArgs) Handles TextBox1.TextChanged
Dim ft As New FormattedText(TextBox1.Text, CultureInfo.GetCultureInfo("en-us"), FlowDirection.LeftToRight, New Typeface("Verdana"), 16, Brushes.Black)
TextBox1.Width = ft.Width
End Sub
End Class
I tried this with my existing solution and the textbox does not appear. I made the DrawingCanvas into a plain Canvas and commented out all the code referring to the DrawingCanvas. And the textbox does appear. The problem is this: I need the functionality in the DrawingCanvas - which derives from Canvas. But because the baseclass methods are Protected, I can't get to them. I can only use them in a derived class, unless there is another way I don't know about.
Any ideas about how to solve this?