Label painting issue when form moved offscreen

[robertybob]

Hi

I have a label which has text that changes dependent on user input using the paint command. Say it says 'Hello World'.

When I drag the form around such that any part of the label goes offscreen, when the label returns to the screen it wants to constantly repaint itself as it returns meaning that, dependent on how fast you drag it back, the label can read 'He He He He Hello World' or 'HHHHHHello World' etc

Is this a known issue and is there a way to prevent it?

The label is simply painted using

Private Sub MyLabel_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyLabel.Paint
 

In order to get it to change appearance it is invalidated when the user clicks a button to tell it to change to some new value. I'm assuming though that there's some core VB process within the painteventargs that triggers when the item gets back to the visible screen that is the root cause of this as all other labels return to the screen just fine.

Thanks!

[Rabbit]

It would help to see the code.

[robertybob]

Here is some code. It's pretty basic.

Option Explicit On
Imports System.ComponentModel
Imports System.Runtime.InteropServices
Imports System.Text
Imports System.Windows.Forms
Imports System
Imports System.IO
Imports System.Collections
Imports System.Threading
 
Public Class Form1
 
Private Sub Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button.Click
        MyLabel.Invalidate()
End Sub
 
Private Sub MyLabel_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyLabel.Paint
        Dim upperfont As Font = New Font("Arial", 10, FontStyle.Bold)
        Dim lowerfont As Font = New Font("Arial", 8, FontStyle.Regular)
        Dim upperbrush As SolidBrush = New SolidBrush(Color.Black)
        Dim lowerbrush As SolidBrush = New SolidBrush(Color.FromArgb(17, 17, 17))
        Dim upperstr As String = myName.Text
        Dim lowerstr As String = myOccupation.Text
        Dim uppersize As SizeF = e.Graphics.MeasureString(upperstr, upperfont, e.ClipRectangle.Size)
        Dim lowersize As SizeF = e.Graphics.MeasureString(lowerstr, lowerfont, e.ClipRectangle.Size)
        e.Graphics.DrawString(upperstr, upperfont, upperbrush, e.ClipRectangle.X + 3 + ((e.ClipRectangle.Width - uppersize.Width) / 2), e.ClipRectangle.Location.Y + 19)
        e.Graphics.DrawString(lowerstr, lowerfont, lowerbrush, e.ClipRectangle.X + ((e.ClipRectangle.Width - lowersize.Width) / 2), e.ClipRectangle.Location.Y + 34)
End Sub
 
End Class
 

[Rabbit]

Did you try clearing it before redrawing?

[robertybob]

Hi Rabbit, I'm learning VB on the job so not sure what you mean by clearing before redrawing. I thought the Invalidate() triggered some kind of clear/redraw? It seems to be redrawing every time the form is moved and fits the label painting to whatever part of the label is showing at the time.

[Rabbit]

But you're only invalidating once. If it's redrawing, you should try invalidating each time. Probably in the dragdrop event.

[robertybob]

Ah ok. Let me investigate the dragdrop - been away for a few days. Thanks Rabbit.

[robertybob]

Not sure Dragdrop is the solution - am looking at trying to determine if the form is being moved but apparently there's no way to do that.

The issue is that this is a static label - it cant be moved within the form. It displays perfectly when you move the form all over the screen. It fails when part of the label goes off the screen edge as I assume that when the form realises that a part that was not visible is now visible again it 'paints' the label. It's that event that I need to kill.

Still checking...

[Rabbit]

You can either subclass the form and look for the WM_MOVE message or use a timer to see if the form has changed location.

[robertybob]

Thanks Rabbit. Might take a look at this later.

At the moment I've added a check named offScreen. When the form Move event is being triggered it checks to see if any part of the form is likely to be outside the screen and, if so, offScreen blocks the painting. It repaints when the form is fully on the screen again.

It's ugly and when label is moved off left side of screen the label is missing text til completely back but this is such a minor part of the application it will do. Was hoping for a simple 'don't repaint when label moving back onscreen' function but not available :)

This isn't going to help many people as it's quite bespoke to my needs but this is the gist of the code I'm running with at the moment.

Private offScreen = 0
Private screenWidth As Integer = 99999
Private screenHeight As Integer = 99999
 
Private Sub Me_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim myScreens() As Screen = Screen.AllScreens
For s = 0 To myScreens.Count - 1
    screenWidth += myScreens(s).Bounds.Width
    screenHeight += myScreens(s).Bounds.Height
Next
End Sub
 
Private Sub MyLabel_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyLabel.Paint
If offScreen = 0 then
' do the painting
End If
End Sub
 
Private Sub Me_Move(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Move
offScreen = 0
If sender.left + Me.Width > screenWidth OrElse sender.top + Me.Height > screenHeight OrElse sender.left < 0 OrElse sender.top < 0 Then offScreen = 1
If offScreen = 0 Then
   MyLabel.Refresh()
End If
End Sub
 
 

[Rabbit]

What if in your Me_Move event you just invalidated the label?

[robertybob]

Ha! Genius! Was working this harder than needed. Seems to work a charm. Many thanks, Rabbit.

[Rabbit]

Glad you got it resolved. Good luck with your project.