Visual Basic

15-May-12 3:52

I have a Picture Box where I use GDI+ to draw lines, circles, etc on. What I have noticed recently is that my other GUI components such as buttons, option boxes, labels, etc. on the same form are not displaying correctly. What I mean by that is they are all black until I click on them or resize the form then it will display properly. However, if I minimize the form then restore the form the GUI components will turn black again.

I did some googling and found out that there seems to be problem with a threading issue. I pin pointed it to my picture box paint event handler. If I comment out the entire event everything displays properly minus what I need to paint in my picture box.

My thinking was maybe I should do some multi-threading so I can get the best of both worlds objects painted in the picture box and my GUI components displaying properly on initial form load.

The first piece of code is my original code with the black showing components. I have tried to use threading in hopes that this will remedy my situation. Because of my limited (near 0) knowledge of threading this may not be the best piece of code. What I get in the threading code is the error picture for my picture box (large red "x" on white background).

'Original Code before threading change.

Private Sub Picture1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Picture1.Paint

myGraphicObject = e.Graphics
myGraphicObject.Clear(Picture1.BackColor)
Draw_GDI_Related_Things_Function()

End Sub

'Threading piece of code
Private Sub Picture1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Picture1.Paint
System.Threading.Monitor.Enter(myGraphicObject)
myGraphicObject= e.Graphics
myGraphicObject.Clear(Picture1.BackColor)

'Draw_GDI_Related_Things_Function uses myGraphicObject to draw unto the picture box.
m_threadDraw = New System.Threading.Thread(New System.Threading.ThreadStart(AddressOf Draw_GDI_Related_Things_Function))

m_threadDraw.Start()
System.Threading.Monitor.Exit(myGraphicObject)
End Sub

Keep in mind that the above code is a before and after.

Can someone help me to understand what I am doing wrong?

Thanks.

Dave Kreskowiak15-May-12 4:13

15-May-12 4:13

Threading is not your solution to black controls.

You cannot touch any property or method of a control from anything other than the UI thread (the thread that created the control instance.) Doing so will only cause bugs that are very difficult to find.

The reason you get the red X is because your drawing code isn't finished yet but the Paint handler already returned control back to the event originator, which is trying to copy the control image to the screen, which you haven't finished drawing yet.

Remove the threading code. You don't need it at all.

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Dave Kreskowiak

Clark Kent12316-May-12 2:22

16-May-12 2:22

Yeah Dave, I figured that was the cause and I went ahead and removed it. That was my initial suspicion as well, but I just wanted someone more knowledgeable than myself to confirm it.

I know this is a tiny bit unrelated, but what my new suspicion is that my data grid view might be the cause of this painting annoyance. I emphasis might because once again I could use your advice.

In my data grid view I have added combo boxes to one column and now I receive this error every time per number of rows I have when I resize the form.
See code below.

Private Sub frmEdit_System_Revised_Resize(sender As Object, e As System.EventArgs) Handles Me.Resize
Me.DataGridViewObj.Width = Me.Width / 2
Me.DataGridViewObj.Top = Me.ComboBoxObj.Top + Me.ComboBoxObj.Height
Me.DataGridViewObj.Height = (Me.MyPictureBox.Top) - (Me.ComboBoxObj.Top + Me.ComboBoxObj.Height)
End Sub

Maybe it's the way I insert data into the combo box inside my datagridview, but I receive this error continiously "datagridviewcomboboxcell value is not valid". I tried Googling this, but the typical reponses are to just suppress this error.

Maybe you can see what I am doing wrong. I would appreciate another set of eyes looking at this and pointing out what the problem is. Or maybe you can refer to me some literature that I can read on how to properly set data to a combobox column.

Inside my insert data sub routine...

Dim objRowData(NumOfColToFill) As Object
Dim newButton As New DataGridViewButtonCell()
Dim newComboBox As New DataGridViewComboBoxCell()
Dim newRowToAdd As New DataGridViewRow()

newRowToAdd.SetValues(objRowData)
Me.DataGridViewObj.Rows.Add(newRowToAdd)

' Initialize the combo box
newComboBox.Items.Add("Data")
newComboBox.Items.Add("Data1")
newComboBox.Items.Add("Data2")
newComboBox.Items.Add("Data3")

Me.DataGridViewObj.Rows.Item(m_intRowCounter).Cells.Item(5) = newComboBox
Me.DataGridViewObj.Rows.Item(m_intRowCounter).Cells.Item(5).Value = "Data"

Me.DataGridViewObj.Rows.Item(m_intRowCounter).Cells.Item(0) = newButton
Me.DataGridViewObj.Rows.Item(m_intRowCounter).Cells.Item(0).Value = "Data"

Thanks!

Dave Kreskowiak16-May-12 4:54

16-May-12 4:54

I have no idea what your form looks like, but you could just use a TableLayoutPanel, properly configured of course, and put your DGV and Combo in adjacent rows. If setup correctly, you can eliminate the Resize code entirely.

The only time I've seen the "DataGridViewComboBox cell value is not valid" is when the value in the combo is not valid for the bound field. You could ignore it, but keep in mind that the error you're seeing is an exception and exceptions are VERY expensive to throw. Your code performance will suffer because of it.

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Dave Kreskowiak

Clark Kent12316-May-12 4:56

16-May-12 4:56

Thanks for that advice. I will look into a Table Layout Panel and see if that will work out. Thumbs Up | :thumbsup:

Dave Kreskowiak16-May-12 7:05

16-May-12 7:05

Also, why are you adding a combobox to the DGV when there's a combobox column available??

It seems you're using the DGV as a kind of storage for your data instead of binding the DGV to a DataTable object and storing the data in there.

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Dave Kreskowiak

Clark Kent12316-May-12 7:27

16-May-12 7:27

Good question.

Well, I have set the column in question as a combo box using the DGV edit column property page. If you will notice in my code I use a variable of the name of newComboBox which is a data type of "DataGridViewComboBoxCell". What my intention was to populate each row with the same data, but each row will have a different selection that can be saved. With that being said if the user saved that layout when the file gets opened I will populate the DGV with the same data, but the currently selected item would be different (if the user decided to select different items). I hope that makes sense.

My thinking was in order to populate each row with pre-defined data the best option was to use the variable newComboBox as mentioned above and reference that to the DGV. It functions as I expected, but the added benefit (sarcasm) I get is the thrown exceptions as I mentioned in my previous response.

You're correct that I am using the DGV differently then I guess what's intended in doing. (Maybe this is root of my problem?). I don't have a DataTable for which it can refer to.

Luc Pattyn15-May-12 14:31

15-May-12 14:31

Dave is right, threading won't help you. Remove it, and the Monitors. And put all painting code in the Paint handler. Here[^] is an article that gives the fundamentals; the examples use C#, the concepts are identical in VB.NET though.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Clark Kent1238-Nov-12 4:30

Changing JPG in picturebox with loop

8-Nov-12 4:30

I had a problem with something about my picturebox.paint_event constantly firing. Still to this day I am clueless as to why. I was about to post a new question in the vb discussion when I came across this discussion I started a while back. I wanted to let you know that link that you posted solved my problem.

My program would draw primitive shapes (circles, lines, letters, etc) onto a picturebox using gdi+, but like I said the picturebox.paint_event would always trigger. This would peg one of my cpus at 100%, rather annoying. After making the changes that website you posted suggested the results are like night and day. Instead of the picturebox I used a panel and the paint_event only triggers when it should be triggered.

I just wanted to circle back and say thanks! Even though quite some time has passed Smile | :)

Dr David Johnson PhD14-May-12 12:02

14-May-12 12:02

Forgive me I am a retired doctor and am just learning programming. I am playing with a small routine that will display number, and signs in rolling boxes to create a kind of slot machine effect to teach my granddaughter math.

I have listed the code below I am having a problem with. It will display the first set of pictures when I click on the button but will not display the pictures in the image list as it randomly selects them.

When I click the next three are moved and displayed but using a loop or a go to statement never works.

I do set the pictures to a default value prior to this routine.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim Reel As Integer

Reelspin:

Dim intpic As Integer
Dim rand As New Random

intpic =rand.Next(0,ImageList3.Images.Count)

Me.PictureBox3.Image = PictureBox2.Image Me.PictureBox2.Image = PictureBox1.Image Me.PictureBox1.Image = ImageList3.Images(intpic)

Reel = (Reel + 1)

If Reel < 10000 Then goto respin

End Sub

I would be very great-full for any help I want to display the pictures as they change in real time.

Dave Kreskowiak14-May-12 13:18

14-May-12 13:18

First, using goto is akin to farting loudly in church. You just don't do it.

It doesn't work because your code is hogging the UI thread. This means that since your code isn't giving up control the UI thread can't process the PAINT messages that are coming into your app from Windows (updating the image you see on screen). The end result it that you only see the last image you set when your loop is done.

How do you get around this?? Forget the loop and use a Timer. Set the Timer to fire an event every 250 milliseconds or so. Start (enable) the Timer in your button Click event.

When your code to change which frame you see will be in the Timer.Tick event. Something like this:

    Private RNG As New Random
.
.
.
    Private Sub MyTimer_Tick(...) Handles MyTimer.Tick
        Dim index As Integer = RNG.Next(0, ImageList3.Images.Count)
        PictureBox3.Image = PictureBox2.Image
        PictureBox2.Image = PictureBox1.Image
        PictureBox1.Image = ImageList3.Images(index)
    End Sub

You don't need to put Me. in front of everything.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

Dr David Johnson PhD14-May-12 15:29

14-May-12 15:29

First THANK YOU for responding so quickly...

Second I feel a dumb as a rock. Being a retired
doctor I thought programming would come a lot
easier to me.

I understand part of what your saying...

That being I have to give the the system time to
update the screen to allow the images to be painted
and seen before the next image appears.

Also I understand how to add the timer and set the value however, I am a little perplexed as to how to call the timer. Do I need to loop back each time until all the images have been displayed? And if so how and where do I call the timer to allow the delay? That is a delay after each image or just after each set?

Thanks again

Luc Pattyn14-May-12 15:43

14-May-12 15:43

A timer periodically fires an event, that is its job. And it is your code that deals with such event, that is what the "Handles myTimer.Tick" says in Dave's code snippet. So you don't provide the looping, the timer does that; you just tell it what to do each time.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Dr David Johnson PhD14-May-12 17:14

14-May-12 17:14

OK now I am more lost than ever...

I understand that I need to slow the process down
and let the images be painted to the screen so each can be seen before it continues to the next image.

I also understand that the timer will do that...

Where I am getting lost is how you call the timer into action. I created it and set the value as suggested to 250. But do I place the code line prior to displaying any image images?

Further, I need to repeat this paint 1,2,3
over and over until the a random timer stops the images from being chosen and displayed.

At this point every time I press the SPIN KEY, or button as it were the images are selected, displayed and with every click they move down one image. Placing a loop, jump or any other kind of repeating function kills the display of any image until the last one, then that is displayed, hence the need for a delay so they can be painted.

If I understand right the timer only need to be activated once and it will fire on its own after that correct? Or do I need to reset the value after each use?

Thanks...

Luc Pattyn14-May-12 17:34

14-May-12 17:34

timer 101:
- create an instance of System.Windows.Forms.Timer
- set its Interval in milliseconds
- give it a Tick handler (a method that "Handles ...Tick"
- launch it by calling its Start method
- DONE: the tick handler will be executed periodically until you explicitly stop the timer.

Yes, the .NET timers are "free running" by default: once started, they keep "ticking" until you stop them. And you can change their Interval any time you like, in case you want the wheels to slow down.

any delay you want is built in the timer, that is what the Interval property is for (e.g. for your alarm clock, the Interval would be 24 hours).

What you need is a "state variable", i.e. one or more data items that know how far your machine has moved. Say you start the timer inside the SpinButton_Click handler, and set a variable "digit" to 0.

Now inside the timer's Tick Handler, you increment "digit" (up to its maximum value, then reset it to zero), and order a repaint of your Form (or a reload of an image in a PictureBox), where the new content depends on "digit". That will make the wheels spin, until you decide it was enough, so you probably need a random number "maxTicks", and after maxTicks ticks of the timer, you stop the timer, and hence the wheels.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Dr David Johnson PhD14-May-12 17:59

14-May-12 17:59

Thanks for all the help

I think I have it now I am going play around with what you have given me and see if I can get it running the way I want.

You have all been life savers...

A not so lost friend...

Dr. Johnson

dg6yhw1115-May-12 6:38

dg6yhw11

15-May-12 6:38

I'd like to amplify the other excellent answers a bit.

I am a VB 6 programmer so I may refer to methods that have changed but they are described in the Help.

You need to have a timer to slow down the process.

Whenever the timer acts, you need to
1 - load the image into the picturebox picturebox.image=...
2 - refresh the picturebox by calling the Refresh picturebox.refresh (may also be Redraw check the Help)
3 - let Windows process the action. application.DoEvents

Its the DoEvents directive that causes Windows to suspend the current thread and process all messages i.e. the picturebox.Refresh method will be executed.

Search the DoEvents in Help for an excellent discussion and sample code. The sample uses a click event from a button but you can just as easily control the process with a timer.

Your images should change whenever the timer ticks.

Murray

Dr David Johnson PhD15-May-12 11:24

15-May-12 11:24

A big THANK YOU to everyone who helped with my problem.

After taking everyone's suggestions I played around with the code and now
have it working just fine. As well I learned a lot from suggestions and
trying different things about the timers and how they work.

By the end of the weekend I should have a working program...

Thanks again...

Luc Pattyn15-May-12 12:06