How can open print dialog box in another thread

Question

If i simply call

If PrintDialog1.ShowDialog = DialogResult.OK Then
                                        PrintDocument1.Print()
                                    End If

its working fine but if i use this function in another thread then it will shows error

{"External component has thrown an exception."}

Why ever would you want to do this? You should always keep all UI events on the main (UI) thread. — Cody Gray - on strike, Aug 17 '11 at 14:51

score 3 · Answer 1 · answered Aug 17 '11 at 14:46

You have to call SetApartmentState on the thread to switch it to STA before you start the thread. This is not possible if the thread is a threadpool thread or if you are using BackgroundWorker.

This is otherwise a bad idea, the dialog won't have a parent and is likely to disappear behind another window. Nor will it act modal. By far the best solution is to display this dialog by code that runs on the main thread. The actual printing can still take place on the worker thread. Use Control.Invoke() as required.

score 1 · Answer 2 · answered Aug 17 '11 at 12:57

1

External threads need to Invoke requests on main UI. You can't directly make a call from a Thread to make UI changes.

answered Aug 17 '11 at 12:57

Shamim Hafiz - MSFT

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score 0 · Accepted Answer · answered Aug 19 '11 at 07:28

0

Create object of PrintDialog in new thread & then call

Dim myPDia As New PrintDialog
 If myPDia.ShowDialog() = Windows.Forms.DialogResult.OK Then
    PrintDocument1.Print()
 End If

answered Aug 19 '11 at 07:28

Sai Sherlekar

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But can anyone give me reason why this happen, why we can not access object of printdialog from one thread to another – Sai Sherlekar Aug 19 '11 at 07:30

How can open print dialog box in another thread

3 Answers3