[RESOLVED] Thread argument

[T120]

Is it possible to pass an argument to a thread and if so how?

[chris128]

You mean when you are creating the thread? If so then yeah you can do it like this:

Dim newthread As New Threading.Thread(AddressOf ThreadWork)
newthread.IsBackground = True
newthread.Start("hello") 'So the string 'hello' is our argument that we are passing in
 
'This is the sub that will be executed on the background thread
Private Sub ThreadWork(ByVal Argument As Object)
        Dim ArgString As String = CStr(Argument)
        'ArgString now contains the string that was passed in to the thread
End Sub

You have to declare the argument as type Object for it to work, so the first thing I usually do in my threads' work sub is to declare some new variables that are of the correct type and convert them using DirectCast (or something like CStr as I have done in the example above)

[T120]

Chris

I thought that was how to do it but with the following I'm getting:-

 Error	1	Overload resolution failed because no accessible 'New' can be called with these arguments:
    'Public Sub New(start As System.Threading.ParameterizedThreadStart)': Option Strict On does not allow narrowing in implicit type conversions between method 'Public Sub GetMissingTile(i As Integer)' and delegate 'Delegate Sub ParameterizedThreadStart(obj As Object)'.
    'Public Sub New(start As System.Threading.ThreadStart)': Method 'Public Sub GetMissingTile(i As Integer)' does not have a signature compatible with delegate 'Delegate Sub ThreadStart()'.	C:\Dot Net 2008 Code\BSGPSV3524\Common.vb	1022	42	BSGPS

and I don't understand the error message

Here is my code:-

 Dim TileDownload As Thread = New Thread(AddressOf MyGPSForm.OSMTiledownload.GetMissingTile)
            TileDownload.Priority = ThreadPriority.Lowest
            '
            '  Fire the thread
            '
            TileDownload.Start(0)

[T120]

OK I understand now - My thread was not expecting the object.

Many thanks for your help

[chris128]

Read my original post again, specifically this part:

You have to declare the argument as type Object for it to work

So change your GetMissingTile method to accept an argument of type Object instead of Integer as you are currently doing

[chris128]

Ah, looks like you got it anyway