Draw Rectangle over PictureBox - vb.net

Question

The next code lets you draw Rectangles in the Form with mouse clics.
Why not, or how can be draw over a PictureBox?
Public Class Form1
Dim SelectRect As Rectangle = New Rectangle()
Dim ps As Point = New Point()
Dim pe As Point = New Point()
This catch the first click, starting point or corner of the rectangle
Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
SelectRect.Width = 0
SelectRect.Height = 0
SelectRect.X = e.X
SelectRect.Y = e.Y
ps.X = e.X
ps.Y = e.Y
pe = ps
End Sub
This part determine the width and height of the rectangle:
Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
If (e.Button = MouseButtons.Left) Then
ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
SelectRect.Width = e.X - SelectRect.X
SelectRect.Height = e.Y - SelectRect.Y
ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
End If
End Sub
This part determine the last coordinate, the second corner of the rectangle:
Private Sub Form1_MouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseUp
Dim g As Graphics = Me.CreateGraphics()
Dim p As Pen = New Pen(Color.Blue, 2)
ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
g.DrawRectangle(p, SelectRect)
g.Dispose()
End Sub
End Class

Answer 1

Your code uses a control (a Form in this case) mouse events to enable the drawing of rectangular shapes, with the help of guidelines, provided by Control.DrawReversibleFrame().
You just have to define the same events of a different, drawable, control - like a PictureBox - and repeat, more or less, the same procedure (after a cleanup).
As many have stated, here and before, use the Graphics object that
the Paint event kindly offers, so that your drawing will persist.
The Graphics object you get from Control.CreateGraphics() is not
persistent, and it can be erase/clipped when you don't want to.
Use it only if that is really what you have planned to do for the
reasons you know.
I've adden an event handler that checks if Control Key is pressed.
If Control is pressed, you add a rectangle, if not, only one rectangle is drawn.
I've also included, as an example, a line of code that fills the rectangle. I think it's interesting, because you have to control the size of the invalidated Region.
Comment out these lines of code to draw just the frame:
SelectRect.Inflate(CInt(-_pen.Width / 2), CInt(-_pen.Width / 2))
e.Graphics.FillRectangle(_brush, SelectRect)
Dim SelectRect As Rectangle = New Rectangle()
Dim _pen As Pen = New Pen(Color.Green, 4)
Dim _brush As SolidBrush = New SolidBrush(Color.Orange)
Dim _ControlPressed As Boolean = False
Private Sub Form1_KeyDown(sender As Object, e As KeyEventArgs) Handles MyBase.KeyDown
_ControlPressed = (e.Modifiers And Keys.Control) = Keys.Control
End Sub
Private Sub Form1_KeyUp(sender As Object, e As KeyEventArgs) Handles Me.KeyUp
_ControlPressed = (e.Modifiers And Keys.Control) = Keys.Control
End Sub
Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
SelectRect.Location = e.Location
SelectRect.Size = New Size(0, 0)
End Sub
Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
If (e.Button = MouseButtons.Left) Then
ControlPaint.DrawReversibleFrame(PictureBox1.RectangleToScreen(SelectRect), PictureBox1.BackColor, FrameStyle.Dashed)
SelectRect.Width = e.X - SelectRect.X
SelectRect.Height = e.Y - SelectRect.Y
ControlPaint.DrawReversibleFrame(PictureBox1.RectangleToScreen(SelectRect), PictureBox1.BackColor, FrameStyle.Dashed)
End If
End Sub
Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
If (e.Y < SelectRect.Y) Then
SelectRect.Location = If(SelectRect.Location.X > e.X,
New Point(e.X, e.Y), New Point(SelectRect.X, e.Y))
SelectRect.Size = New Size(Math.Abs(SelectRect.Width), Math.Abs(SelectRect.Height))
Else
If SelectRect.Location.X > SelectRect.Right Then
SelectRect.Location = New Point(e.X, SelectRect.Y)
SelectRect.Size = New Size(Math.Abs(SelectRect.Width), Math.Abs(SelectRect.Height))
End If
End If
If _ControlPressed Then
Dim _InflatedRect As Rectangle = New Rectangle(SelectRect.Location, SelectRect.Size)
_InflatedRect.Inflate(CInt(_pen.Width / 2), CInt(_pen.Width / 2))
PictureBox1.Invalidate(_InflatedRect)
Else
PictureBox1.Invalidate()
End If
End Sub
Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
'Draw the outer rectangle with the color of _pen
e.Graphics.DrawRectangle(_pen, SelectRect)
'Fill the rectangle with the color of _brush
'It's half Pen.Width smaller so it doesn't erase the contour
SelectRect.Inflate(CInt(-_pen.Width / 2), CInt(-_pen.Width / 2))
e.Graphics.FillRectangle(_brush, SelectRect)
End Sub