Move and Resize a Control or a Borderless Form - using window messages (smooth!)

[NickThissen]

Hi,

Here is a small example of how to move and resize a form without a border (FormBorderStyle = None).

Instead of manually setting the Location and Size of the Form, I have decided to use the SendMessage function to handle it. This results in a much smoother experience, (especially with lots of controls) and will also make sure that the form always follows the mouse, regardless of how fast you move it. In other examples you will often notice that if you move your mouse too fast, the form can no longer keep up and will stop moving.


The example uses a Panel as the form's caption. Dragging the panel will move the form, just like the real caption of a form with a border would behave.
You can of course decide to use a different control. You could even use the form itself. I just thought a Panel was the easiest example.

For resizing, I did not use any special controls; I merely use a BorderWith constant (default: 6) that defines the width of the area you can use to resize the form.

Screenshot:

(You can of course use nice icons for the buttons instead, but that was not the purpose of this codebank submission)



The form moving works pretty simple: when the MouseDown event of the Panel is fired, a simple check is done to make sure that the user clicked the Left button instead of the Right button, and that the form is not maximized (you cannot move a maximized form).
Then, a MoveForm() method is called, in which the SendMessage function is called with the correct parameters.

Private Sub pnlCaption_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles pnlCaption.MouseDown
        If e.Button = Windows.Forms.MouseButtons.Left And Me.WindowState <> FormWindowState.Maximized Then
            MoveForm()
        End If
    End Sub
 
    Private Sub MoveForm()
        ReleaseCapture()
        SendMessage(Me.Handle, WM_NCLBUTTONDOWN, HTCAPTION, 0)
    End Sub

The resizing is a little more involved, as it requires a check for the position of the mouse cursor, and changes the cursor to a resizing cursor.
For this, I made a Property resizeDir which changes the cursor depending on which value it gets automatically.
The value of this property is used in a ResizeForm method, which calls the SendMessage function again with the correct parameters (depending on the position of the mouse, or the resizeDir value).

Private Sub Form1_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseDown
        If e.Button = Windows.Forms.MouseButtons.Left And Me.WindowState <> FormWindowState.Maximized Then
            ResizeForm(resizeDir)
        End If
    End Sub
 
    Private Sub Form1_MouseMove(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseMove
        'Calculate which direction to resize based on mouse position
 
        If e.Location.X < BorderWidth And e.Location.Y < BorderWidth Then
            resizeDir = ResizeDirection.TopLeft
 
        ElseIf e.Location.X < BorderWidth And e.Location.Y > Me.Height - BorderWidth Then
            resizeDir = ResizeDirection.BottomLeft
 
        ElseIf e.Location.X > Me.Width - BorderWidth And e.Location.Y > Me.Height - BorderWidth Then
            resizeDir = ResizeDirection.BottomRight
 
        ElseIf e.Location.X > Me.Width - BorderWidth And e.Location.Y < BorderWidth Then
            resizeDir = ResizeDirection.TopRight
 
        ElseIf e.Location.X < BorderWidth Then
            resizeDir = ResizeDirection.Left
 
        ElseIf e.Location.X > Me.Width - BorderWidth Then
            resizeDir = ResizeDirection.Right
 
        ElseIf e.Location.Y < BorderWidth Then
            resizeDir = ResizeDirection.Top
 
        ElseIf e.Location.Y > Me.Height - BorderWidth Then
            resizeDir = ResizeDirection.Bottom
 
        Else
            resizeDir = ResizeDirection.None
        End If
    End Sub
 
Private Sub ResizeForm(ByVal direction As ResizeDirection)
        Dim dir As Integer = -1
        Select Case direction
            Case ResizeDirection.Left
                dir = HTLEFT
            Case ResizeDirection.TopLeft
                dir = HTTOPLEFT
            Case ResizeDirection.Top
                dir = HTTOP
            Case ResizeDirection.TopRight
                dir = HTTOPRIGHT
            Case ResizeDirection.Right
                dir = HTRIGHT
            Case ResizeDirection.BottomRight
                dir = HTBOTTOMRIGHT
            Case ResizeDirection.Bottom
                dir = HTBOTTOM
            Case ResizeDirection.BottomLeft
                dir = HTBOTTOMLEFT
        End Select
 
        If dir <> -1 Then
            ReleaseCapture()
            SendMessage(Me.Handle, WM_NCLBUTTONDOWN, dir, 0)
        End If
    End Sub

I attached the full example (without any compiled files, so you will probably need to Build it first) so you can play around with it.

Enjoy!