chadmanvb
asked on
background worker passing text to label and listview on main form .net visual basic
I would like to move a process to a background worker. I need it to pass 2 varibles to the background worker, have it run a process, then return back 2 variables. How can I do that?
dim str1 ="test1"
dim str2=test3"
BackgroundWorker1.RunWorke
Private Sub BackgroundWorker1_DoWork(B
End Sub 'return updated str1 and str2
dim str1 ="test1"
dim str2=test3"
BackgroundWorker1.RunWorke
Private Sub BackgroundWorker1_DoWork(B
End Sub 'return updated str1 and str2
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Éric Moreau
also check http://emoreau.com/Entries/Articles/2006/12/The-BackgroundWorker-component.aspx
just for your label text change:
Private Sub SetVariable(ByVal StrVar As String)
MyLabel.text = StrVar
End Sub
Both good answers. Sometimes I mix the two approaches together.
As demonstrated in Eric's article, you can pass in a parameter to the RunWorkerAsync() method. If you have multiple values, then you can use a List(Of String), a simple array, or create a custom class to hold the values. The important part here, though, is to cast "e.Argument" in the DoWork() handler back to whatever type you passed in so you can access the values within.
Similarly, you pass things OUT of the DoWork() handler by setting "e.Result" to something. Again, you can pass out whatever type you want if you need to pass multiple items. Just cast "e.Result" back to the correct type in the RunWorkerCompleted() event.
*The same thing can be done with ReportProgress() and the ProgressChanged() event. There is an overload of ReportProgress() that accepts two parameters, with the second parameter being used to pass out information other than a simple integer for progress. The "e.UserState" parameter in the ProgressChanged() event is then cast back to the correct type so you can access the values within.
As demonstrated in Eric's article, you can pass in a parameter to the RunWorkerAsync() method. If you have multiple values, then you can use a List(Of String), a simple array, or create a custom class to hold the values. The important part here, though, is to cast "e.Argument" in the DoWork() handler back to whatever type you passed in so you can access the values within.
Similarly, you pass things OUT of the DoWork() handler by setting "e.Result" to something. Again, you can pass out whatever type you want if you need to pass multiple items. Just cast "e.Result" back to the correct type in the RunWorkerCompleted() event.
*The same thing can be done with ReportProgress() and the ProgressChanged() event. There is an overload of ReportProgress() that accepts two parameters, with the second parameter being used to pass out information other than a simple integer for progress. The "e.UserState" parameter in the ProgressChanged() event is then cast back to the correct type so you can access the values within.
>BackgroundWorker1.RunWork
>End Sub 'return updated str1 and str2
Approaches described above are proper approaches but given that these are variables not controls on UI thread and you need to set them BEFORE calling worker and read them AFTER worker has completed, you can simply declare these as class level variables. Set these before calling the worker and read them back after worker has completed.
>End Sub 'return updated str1 and str2
Approaches described above are proper approaches but given that these are variables not controls on UI thread and you need to set them BEFORE calling worker and read them AFTER worker has completed, you can simply declare these as class level variables. Set these before calling the worker and read them back after worker has completed.
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