How-To Allow the User to Resize Controls on a Form at Runtime

Introduction
In my previous postI showed how to let the user move a TextBox on the form at run-time using the mouse.
I am going to take this one step further and show how to let the user resize the TextBox when clicking and draging on the borders of the TextBox.

The Example
I only implemented resizing the width (left/right) of the control (This is a regular TextBox - no meaning to resizing vertically). You can apply the same algorithm to program vertical resizing yourself. The code is in VB.NET.
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Private _mouseDown As Boolean = False
Private _initialMouseX As Integer
Private _initialMouseY As Integer
Private _initialWidth As Integer

Private Enum Borders
   Left
   Right
   None
End Enum
Private _resizeType As Borders = Borders.None

Private Sub textBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles textBox1.MouseDown
   _mouseDown = true
   _resizeType = GetBorder(e.X, e.Y)
   _initialMouseX = e.X
   _initialMouseY = e.Y
   _initialWidth = textBox1.Width
End Sub

Private Function GetBorder(int x, int y) As Borders
   If (x<5 And x>-5) Then _
      Return Borders.Left
   If (x>textBox1.Width-10 And x<textBox1.Width+10) Then _
      Return Borders.Right
   Return Borders.None
End Function

Private Sub textBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles textBox1.MouseUp
   _mouseDown = false
   Me.Cursor = Cursors.Arrow
   _resizeType = Borders.None
End Sub

Private Sub textBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles textBox1.MouseMove
   If (Not _mouseDown) Then
      If (GetBorder(e.X, e.Y) <> Borders.None) Then
         Me.Cursor = Cursors.SizeWE
      Else
         Me.Cursor = Cursors.Arrow
      End If
      Return
   End If
   If (_resizeType = Borders.None) Then
      Dim deltaX As Integer = e.X - _initialMouseX
      Dim deltaY As Integer = e.Y - _initialMouseY
      textBox1.Left += deltaX
      textBox1.Top += deltaY
   Else
      Dim deltaX As Integer = e.X - _initialMouseX
      Select Case _resizeType
         Case Borders.Left:
            If (textBox1.Width - deltaX>0) Then
               textBox1.Left += deltaX
               textBox1.Width -= deltaX
            End If
      Case Borders.Right:
            If (_initialWidth + deltaX>0) Then _
               textBox1.Width = _initialWidth + deltaX
      End Select
   End If
End Sub

Private Sub textBox1_MouseLeave(sender As Object, e As EventArgs) Handles textBox1.MouseLeave
   Me.Cursor = Cursors.Arrow;
End Sub

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When the user click on the control we check if the mouse is on the border (GetBorder method) and sample the initial width of the control . The actual resize is done in the MouseMove event handler. It is done by changing the Width property of the control (calculated comparing the initial width).