Help: buggy activity in compact .net app

Sarah Smith · Jan 31, 2004

Hi Guys,

I am learning to code .Net apps for my PDA. To start with, i'm making
a slide show app.

I have a string array which holds the names of image files found in a
folder on the device on an SD Card. The app then loops through this
array moving through the elements once avery couple of seconds
(timer).

I then us this code to create a bitmap from the path

strFullpath = "\SD Card\" & strFilesarray(x)

'where X is the loop counter.

Before I call the function to grab a bitmap from the file/path, I
check that the string is not empty. So far, so good:

If strFullPath = "" Then
MsgBox("Error: path string empty!")
Return
End If

'I then do this:

Dim myBitMap As Bitmap

myBitMap = MakeBitMap(strFullPath)

'Here are the guts of my MakeBitmap function:

Private Function MakeBitMap(ByVal strPath As String) As Bitmap

Try
Dim MyBitmap As New Bitmap(strPath) '*error occurs here
Return MyBitmap

Catch ex As Exception
MsgBox("Error: " & ex.Message & " in MakeBitMap()")
Return Nothing
End Try

End Function

As you can see, it is pretty straight forward. But ... after looping
successfully for the first time, the app generates an error
(BadArgumentException) about half way through the second loop.

I know the filepath is good because of the check it makes before
calling the MakeBitmap() function.

Does anyone have an idea as to what could be causing the error?

Alex Feinman [MVP] · Jan 31, 2004

Before invoking MakeBitmap to load anothe bitmap, try calling .Dispose on
the one you had already.

Something like this:
If Not myBitmap is Nothing Then
myBitmap.Dispose()
End if

myBitmap = MakeBitmap(...)

Alex Yakhnin, MVP · Jan 31, 2004

And also make sure that the file actually exists:

If File.Exists(strPath) Then
/'bla, bla bla
End if

Sarah Smith · Feb 1, 2004

Hi Alex,

thanks for your suggestions.

I think the code is OK, and the error is a bug in the CF.

I don't need to check the path (as you indicate below), because the
path has been verified earlier.

As for using .Dispose() on the bitmap object ... I don't think that is
usefull either because the bitmap is created inside a routine.

Like this:

Dim strFullPath As String
strFullPath = strRoot & "\" & strFilenames(nCount)

If strFullPath = "" Then
MsgBox("Error: path string empty!")
Return
End If

Dim myBitMap As Bitmap
myBitMap = MakeBitMap(strFullPath)

If myBitMap Is Nothing Then
MsgBox("Error with: " & strFilenames(nCount))
Return
End If

I moved the code in the MakeBitmap() function just to handle debugging
a little better. So as you can see, each time the code is ready to
call the MakeBitMap() function, it creates a New Bitmap anyway.

Or is the CF runtime doing something that is not normal?

I always thought that when you enter a routine, local variables are
created, and then when the routine loses scope, and you are returned
to the calling routine, the local variables are destroyed.

Doesn't the CF runtime work this way?

-SS

Chris Tacke, eMVP · Feb 1, 2004

The variable is destroyed, but there is nothing to guarantee immediate
disposal of the resources it needed. Calling Dispose (and maybe even
GC.Collect) would help the EE know what to do. Myself I'd probably use a
class-scoped variable for the bitmap that I create only once per app
instance. This would avoid the entire situation.

-Chris

Alex Feinman [MVP] · Feb 1, 2004

Actually the whole point of doing what I suggested was to make sure bitmap
data is freed from memory *before* the next one is loaded. She might only
have enough memory for one bitmap

Alex Feinman [MVP] · Feb 1, 2004

Sara,

Why don't you at least try the suggested steps? As it happens, nearly 100%
of developers think their code is ok and there is something wrong with
OS/Library/Framework. After dust settles, only 99% of them have proven
themselves right.

That said, there *are* bugs in CF, but to confirm it someone will need to
see repro code

Chris Tacke, eMVP · Feb 2, 2004

Out of curiosity (and because I know you've looked at this stuff and I
haven't), if she went with a single global and re-loaded it as needed, what
are the memory implications? Does an entirely new block get allocated when
the Bitmap is reloaded with another image, or is the original memory chunk
re-used if possible?

-Chris

Sarah Smith · Feb 2, 2004

Thank you both. I will try the steps you mentioned.

I'll post back the results if you're interested.

Thanks a lot.

S.S

Sarah Smith · Feb 2, 2004

Hi,

It still doesn't work correctly.

This is all of the code from the 2 routines. The first one:
Showimage() is called either from a navigation button, or from a Timer
event (for a slide show).

The variables: strRoot and strFilenames() are populated in button or
form events:

The error message is always "Bad Argument Exception" when trying to
create a new bitmap in the MakeBitmap() function.

The app can loop through about 40 images, but on the second run, it
raises the exception about have way through.

FYI: the images are stored on an SD Card, are JPG format, and the
device and os is a Dell Axim X5 with WM 2003.

the error does _not_ occur in the emulator.

S.S

Private Sub ShowImage()

On Error GoTo Trap
'Picture box width: 224, hieght: 232
Me.picBox1.Width = 224
Me.picBox1.Height = 232
Me.picBox1.SizeMode = PictureBoxSizeMode.StretchImage

Me.Text = strFilenames(nCount).ToString

Dim strFullPath As String
strFullPath = strRoot & "\" & strFilenames(nCount)

If strFullPath = "" Then
MsgBox("Error: path string empty!")
Return
End If

Dim myBitMap As Bitmap

If Not myBitMap Is Nothing Then
myBitMap.Dispose()
End If

myBitMap = MakeBitMap(strFullPath)

If myBitMap Is Nothing Then
MsgBox("Error with: " & strFilenames(nCount))
Return
End If

If myBitMap.Width < Me.picBox1.Width Then

Else
'The aspect ratio of an image is the width / hieght
'get the aspect ratio of the image:
Dim aspInt As Double
aspInt = myBitMap.Width / myBitMap.Height
Me.picBox1.Height = CInt(Me.picBox1.Width / aspInt)
Me.picBox1.SizeMode = PictureBoxSizeMode.StretchImage

End If

'Set the new bitmap to be the Image of the picture box:
Me.picBox1.Image = myBitMap

Exit Sub

Trap:
MsgBox("Error: " & Err.Description & " ..in ShowImage()")
'Resume Next
Timer1.Enabled = False

End Sub

Private Function MakeBitMap(ByVal strPath As String) As Bitmap

Try
Dim MyBitmap As Bitmap
If Not MyBitmap Is Nothing Then
MyBitmap.Dispose()
End If

MyBitmap = New Bitmap(strPath) '<---error here
Return MyBitmap

Catch ex As Exception
MsgBox("Error: " & ex.Message & " in MakeBitMap()")
Return Nothing
End Try

End Function

Alex Feinman [MVP] · Feb 2, 2004

Is it a SanDisk SD card? Can you try doing this on another device?

Alex Feinman [MVP] · Feb 2, 2004

I don't see that it possibly could reuse the memory. If the 1st bitmap was
disposed, then the memory is available and if it was not, then the memory is
still in use and is untouchable.

Chris Tacke, eMVP · Feb 2, 2004

I guess my question is this. How would this impact memory, assuming
"bitmaps" is an array of string paths?

Bitmap b;

for(i = 0 ; i < bitmaps.count ; i++)
{
b = new Bitmap(bitmaps.ToString());
}

--
Chris Tacke, eMVP
Co-Founder and Advisory Board Member
www.OpenNETCF.org
---
Windows CE Product Manager
Applied Data Systems
www.applieddata.net

Alex Feinman said:
I don't see that it possibly could reuse the memory. If the 1st bitmap was
disposed, then the memory is available and if it was not, then the memory is
still in use and is untouchable.

Chris Tacke said:

Out of curiosity (and because I know you've looked at this stuff and I
haven't), if she went with a single global and re-loaded it as needed, what
are the memory implications? Does an entirely new block get allocated when
the Bitmap is reloaded with another image, or is the original memory chunk
re-used if possible?

-Chris

Alex Feinman said:

Actually the whole point of doing what I suggested was to make sure bitmap
data is freed from memory *before* the next one is loaded. She might only
have enough memory for one bitmap

"Chris Tacke, eMVP" <ctacke[at]Open_NET_CF[dot]org> wrote in message
The variable is destroyed, but there is nothing to guarantee immediate
disposal of the resources it needed. Calling Dispose (and maybe even
GC.Collect) would help the EE know what to do. Myself I'd probably

Click to expand...

use

a
class-scoped variable for the bitmap that I create only once per app
instance. This would avoid the entire situation.

-Chris

Hi Alex,

thanks for your suggestions.

I think the code is OK, and the error is a bug in the CF.

I don't need to check the path (as you indicate below), because the
path has been verified earlier.

As for using .Dispose() on the bitmap object ... I don't think

Click to expand...

Click to expand...

that

is

Click to expand...

Sarah Smith · Feb 2, 2004

The card is manufactured in taiwan by Apacer. (32mb).

.... I've just tried moving the images to the My Documents\My
Pictures folder ... with the same result.

"Error: ArgumentException in MakeBitMap()"

... so it's not the card :-(
S.S

Serg Kuryata [MS] · Feb 3, 2004

Alex Feinman [MVP] · Feb 3, 2004

Sara,

I just realized that you code still succeptible to the same problem. You are
not disposing of the bitmap correctly. Consider replacing your code with
this:

Private Sub ShowImage()

On Error GoTo Trap
'Picture box width: 224, hieght: 232
Me.picBox1.Width = 224
Me.picBox1.Height = 232
Me.picBox1.SizeMode = PictureBoxSizeMode.StretchImage

Me.Text = strFilenames(nCount).ToString

Dim strFullPath As String
strFullPath = strRoot & "\" & strFilenames(nCount)

If strFullPath = "" Then
MsgBox("Error: path string empty!")
Return
End If

Dim myBitMap As Bitmap

' The reason for this acrobatics is that I'm not sure if Picturebox
' can handle correctly calling Dispose on its active bitmap
myBitMap = Me.picBox1
Me.picBox1 = Nothing

If Not myBitMap Is Nothing Then
myBitMap.Dispose()
myBitMap = Nothing
End If

Try
myBitMap = new Bitmap(strFullPath)
Catch ex As Exception
MsgBox("Error: " & ex.Message & " in MakeBitMap()")
Return
End Try

If myBitMap.Width < Me.picBox1.Width Then

Else
'The aspect ratio of an image is the width / hieght
'get the aspect ratio of the image:
Dim aspInt As Double
aspInt = myBitMap.Width / myBitMap.Height
Me.picBox1.Height = CInt(Me.picBox1.Width / aspInt)
Me.picBox1.SizeMode = PictureBoxSizeMode.StretchImage

End If

'Set the new bitmap to be the Image of the picture box:
Me.picBox1.Image = myBitMap

Exit Sub

Trap:
MsgBox("Error: " & Err.Description & " ..in ShowImage()")
'Resume Next
Timer1.Enabled = False

End Sub

Sarah Smith · Feb 3, 2004

Bingo!

Sergiy's suggestion did the trick!

Adding this code ...

If Not (Me.picBox1.Image Is Nothing) Then
Me.picBox1.Image.Dispose()
End If

Me.picBox1.Image = myBitMap

.... seems to have solved the problem.

Thank you very much for your help. You've restored my faith!

You guys have been great.

S.S

Serg Kuryata [MS] · Feb 3, 2004

Help: buggy activity in compact .net app

Sarah Smith

Alex Feinman [MVP]

Alex Yakhnin, MVP

Sarah Smith

Chris Tacke, eMVP

Alex Feinman [MVP]

Alex Feinman [MVP]

Chris Tacke, eMVP

Sarah Smith

Sarah Smith

Alex Feinman [MVP]

Alex Feinman [MVP]

Chris Tacke, eMVP

Sarah Smith

Serg Kuryata [MS]

Alex Feinman [MVP]

Sarah Smith

Serg Kuryata [MS]