How to temporarily pause processing

Question

This question is about a mapping application I am writing, specifically how to coordinate processing and mouse actions.

To add a new point to a map, this routine is called:

Private Sub AddPoint() 
	PostAllPoints()   'Show all existing points
	Points.Clear()   'Clear saved points
	<<STOP HERE>>
	Dim win As New GeoElementParameters
	....
End Sub

After existing points are cleared, I want processing to stop so the user can create a new point using the following method:

Private Sub CreatePoint(sender As Object, e As MouseButtonEventArgs) Handles map.MouseLeftButtonUp
	If Keyboard.Modifiers = ModifierKeys.Control Then
		Dim pt As Point = map.ScreenToGeographic(e.GetPosition(map))
		Points.Add(pt)
		PostMark(pt, vl, Brushes.Red)
	End If
End Sub

After the user creates a point I want the processing to continue after the <<STOP HERE>> line in the AddPoint routine.

I've read up on Async methods but can't put theory into practice. What is the best way to accomplish this?

Answer 1

Hi @RogerSchlueter-7899 ,

You need to pause execution at <<STOP HERE>> in AddPoint() until the user interacts with the map and creates a point using a TaskCompletionSource.

Imports System.Threading.Tasks

Private _pointCompletionSource As TaskCompletionSource(Of Point)

Private Async Sub AddPoint()
    PostAllPoints() ' Show all existing points
    Points.Clear()  ' Clear saved points

    ' Create a new TaskCompletionSource
    _pointCompletionSource = New TaskCompletionSource(Of Point)()

    ' Wait for user to create a point
    Dim newPoint As Point = Await _pointCompletionSource.Task

    ' Continue processing after the user adds a point
    Dim win As New GeoElementParameters()
End Sub

Private Sub CreatePoint(sender As Object, e As MouseButtonEventArgs) Handles map.MouseLeftButtonUp
    If Keyboard.Modifiers = ModifierKeys.Control AndAlso _pointCompletionSource IsNot Nothing Then
        Dim pt As Point = map.ScreenToGeographic(e.GetPosition(map))
        Points.Add(pt)
        PostMark(pt, vl, Brushes.Red)

        ' Complete the TaskCompletionSource with the selected point
        _pointCompletionSource.TrySetResult(pt)
    End If
End Sub

Best Regards.

Jiachen Li

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