Creating New Form Controls in Visual Basic - vb.net

Question

I am trying to have a button, when clicked, creates a new picturebox control. So that everytime I click it, it adds another new picturebox control. These pictureboxes will all have the same functions like being able to move them around and draw on them. But the button only makes one and no more after that with the following code. What am I missing?
Public Class Form1
Dim xpos As New Integer
Dim ypos As New Integer
Dim pos As New Point
Dim x As Integer
Dim y As Integer
Dim canvas As New PictureBox
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim i As Integer = 0
i = i + 1
canvas.Name = "canvas" & i
canvas.BackColor = Color.White
canvas.BorderStyle = BorderStyle.FixedSingle
canvas.Image = Nothing
canvas.Height = TextBox1.Text
canvas.Width = TextBox2.Text
AddHandler canvas.MouseDown, AddressOf PictureBox1_MouseDown
AddHandler canvas.MouseMove, AddressOf PictureBox1_MouseMove
Controls.Add(canvas)
End Sub
Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
xpos = Cursor.Position.X - canvas.Location.X
ypos = Cursor.Position.Y - canvas.Location.Y
End Sub
Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
If e.Button = Windows.Forms.MouseButtons.Left Then
pos = MousePosition
pos.X = pos.X - xpos
pos.Y = pos.Y - ypos
canvas.Location = pos
End If
End Sub
Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
End Class

Answer 1

Dim canvas As New PictureBox
You have multiple bugs in your code but this is the most serious one. The As New syntax ensures that you'll always create a PictureBox object, but it will only ever be one object. And of course, one variable cannot keep track of multiple picture boxes.
What you need to do is create a new one ever time the button is clicked. It is generally a good idea to keep track of the picture boxes you create. So correct code looks like:
Dim canvases As New List(Of PictureBox)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim canvas = New PictureBox
canvases.Add(canvas)
canvas.Name = "canvas" & canvases.Count.ToString()
'' etc...
End Sub
Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
Dim canvas = DirectCast(sender, PictureBox)
xpos = Cursor.Position.X - canvas.Location.X
ypos = Cursor.Position.Y - canvas.Location.Y
End Sub
Note how the sender argument gives you a reference back to the picture box object that's being moused. Do the same thing in any other event handlers.

Answer 2

Increasing the counter whenever a new canvas is created:
Public Class Form1
Dim counter As New Integer
...
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
counter += 1
canvas.Name = "canvas" & counter.ToString()
...
Accessing the canvas that the mouse is currently moving over:
Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
If e.Button = Windows.Forms.MouseButtons.Left Then
pos = MousePosition
pos.X = pos.X - xpos
pos.Y = pos.Y - ypos
DirectCast(sender, PictureBox).Location = pos
End If
End Sub