Form flickers too much on mouse move event - vb.net

Question

I wrote the following procedure to move and dock a borderless window:
Public Class frmNavigation
Inherits Form
'Declarations to allow form movement on mouse down
Private IsFormBeingDragged As Boolean = False
Private MouseDownX As Integer
Private MouseDownY As Integer
Dim Xs As Integer
Dim Ys As Integer
Dim DockScale As Integer
Private Sub frmNavigation_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseDown
'This procedure allows the user to move the form when the
'mouse button is down. The form does not have borders, so it
'needs to be coded to move.
If e.Button = MouseButtons.Left Then
IsFormBeingDragged = True
MouseDownX = e.X
MouseDownY = e.Y
End If
End Sub
Private Sub frmNavigation_MouseUp(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseUp
'This procedure allows the user to move the form when the
'mouse button is up. The form does not have borders, so it
'needs to be coded to move.
If e.Button = MouseButtons.Left Then
IsFormBeingDragged = False
End If
End Sub
Private Sub frmNavigation_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseMove
'This procedure allows the user to move the form when the
'mouse button is dragging the form. The form does not have borders, so it
'needs to be coded to move.
Dim curScreen As Screen
curScreen = Screen.PrimaryScreen 'curScreen = Screen.AllScreens(0)
Dim height As Integer = curScreen.Bounds.Height
Dim width As Integer = curScreen.Bounds.Width
width = curScreen.WorkingArea.Width
height = curScreen.WorkingArea.Height
If IsFormBeingDragged Then
Dim temp As System.Drawing.Point = New System.Drawing.Point()
Xs = MouseDownX
Ys = MouseDownY
temp.X = Me.Location.X + (e.X - MouseDownX)
temp.Y = Me.Location.Y + (e.Y - MouseDownY)
Me.Location = temp
temp = Nothing
End If
End Sub
End Class
So far, this works as designed, it moves the form without any issue whatsoever. The issue starts when I add code to dock the form under the mouse move event as:
Private Sub frmNavigation_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseMove
'This procedure allows the user to move the form when the
'mouse button is dragging the form. The form does not have borders, so it
'needs to be coded to move.
Dim curScreen As Screen
curScreen = Screen.PrimaryScreen 'curScreen = Screen.AllScreens(0)
Dim height As Integer = curScreen.Bounds.Height
Dim width As Integer = curScreen.Bounds.Width
width = curScreen.WorkingArea.Width
height = curScreen.WorkingArea.Height
If IsFormBeingDragged Then
Dim temp As System.Drawing.Point = New System.Drawing.Point()
Xs = MouseDownX
Ys = MouseDownY
temp.X = Me.Location.X + (e.X - MouseDownX)
temp.Y = Me.Location.Y + (e.Y - MouseDownY)
Me.Location = temp
temp = Nothing
End If
If IsFormBeingDragged = True And e.Button = MouseButtons.Left Then
'if the drag flag is true and left mouse button is pressed...
'set Top side docking
If Me.Top + (MouseDownY - Ys) < DockScale Then
Me.Top = 0
Exit Sub
End If
'set bottom side docking
If Me.Top + (MouseDownY - Ys) + Me.Height > (height - DockScale) Then
Me.Top = height - Me.Height
Exit Sub
End If
'move the form finally
Me.Left = Me.Left + (MouseDownX - Xs)
Me.Top = Me.Top + (e.Y - Ys)
End If
End Sub
When I add the code for docking and I try to move the form, it moves and it docks, but it flickers like crazy when holding the mouse down and moving. I can't see why this happens, is the first time I dabble with something like this, so I am not sure where I am going wrong.

Answer 1

In your block of code with the dock check, the first "If" block sets to location of the form based on the mouse position, then later, in the 2nd and 3rd "If" block, sets the position based on docking. This is causing the to form move around twice one each mouse movement. You need some kind of flag that indicates that the form is in a docked state and then not move the form at all while this flag is set.

Answer 2

From what I see you should first check if form is docked and then set proper location for it.
Just like this you first set location, then you set Top, so form is moved twice and it flickers...

Answer 3

I faced a problem similar to this and it turned out to be caused by the form's TransparencyKey.
Try deleting the set color.