How does one deal with the "Cannot acces a disposed object" error?

Question

My program involves accessing a print preview dialog. When a button is clicked, the code is:

        PrintPreviewDialog1.Document = PrintDocument1
        PrintPreviewDialog1.Show()

It works just fine the first time. However, when I close the printpreviewdialog and then try to open it again (through the button) in the same run then I get a "cannot access a disposed object" runtime error. Hence, it can only work once during a program run and I need it to do more.

How can this problem be fixed?

Answer 1

Hi,

Do not dispose of the PrintPreviewDialog at any point in your code and your problem will be solved I reckon.  :)

Can you post your code to show where you are getting the error?

If that is all you have you could do this.>>

Public Class Form1

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

        If PrintPreviewDialog1 Is Nothing Then
            PrintPreviewDialog1 = New PrintPreviewDialog
        End If

        PrintPreviewDialog1.Document = PrintDocument1
        PrintPreviewDialog1.Show()

    End Sub

End Class

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Regards,

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Answer 2

What is the object that has been disposed?  When the error occurs, hover the mouse over each object referred to in that line of code.  Which ones are reported as available objects and which ones are reported as Nothing?

Answer 3

What is the object that has been disposed?  When the error occurs, hover the mouse over each object referred to in that line of code.  Which ones are reported as available objects and which ones are reported as Nothing?

That's what I was about to type - I think he's confusing what's disposed.

I'll be curious so see what he finds on this.

Answer 4

PrintPreviewDialog is a dialogue box - the clue is in the name.

Therefore it should be shown using ShowDialog.

Then when you close it it doesn't close, it just hides.

Answer 5

PrintPreviewDialog is a dialogue box - the clue is in the name.

Therefore it should be shown using ShowDialog.

Then when you close it it doesn't close, it just hides.

Why not create it then intentionally dispose it, ergo "Using ppd As New PrintPreviewDialog"?

Then in the Using block, use ".ShowDialog"? That's what came to my mind, but in all fairness, I don't use it - I have third party stuff that does all that for me but unless it's intrinsically different ...?

Answer 6

That's what I would do but if you add one to the form from the toolbox, show it using .Show and then click the close button it behaves like any other form and disposes of itself.  So next time you try you get the exception because, unlike other forms it doesn't auto instantiate.

Question is why have they coded it like this when all the other dialogues only have a ShowDialog method and not a .Show

Answer 7

That's what I would do but if you add one to the form from the toolbox, show it using .Show and then click the close button it behaves like any other form and disposes of itself.  So next time you try you get the exception because, unlike other forms it doesn't auto instantiate.

Question is why have they coded it like this when all the other dialogues only have a ShowDialog method and not a .Show

Right, the same as a FileDialog.

@PRS-> Reconsider how you're doing this. Despite that you've found your answer, I think that in the long-run you'll find it more helpful to create it in code, instantiate a new one each time, and do it all in a Using block so that you're intentionally completely doing away with all resources associated with it once used.

It's not difficult at all but if you need help, just ask.

Good luck with your project. :)