How do I ensure only a single r/l click is added to my listbox?

Hey Ralf, thanks for your patience. By this I mean an application, different to my actual form, is embedded inside my form space. This is acheived through this code:
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<dllimport("user32.dll")> Public Shared Function SetParent(ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr
End Function
<dllimport("user32.dll")> Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
End Function
Private Const WM_SYSCOMMAND As Integer = &H112
Private Const SC_MAXIMIZE As Integer = &HF030

Private Sub SetChildTimer_Tick(sender As Object, e As EventArgs) Handles SetChildTimer.Tick
Dim ClientProcess As Process = Process.GetProcessesByName("notepad").FirstOrDefault

If ClientProcess IsNot Nothing Then

SetParent(ClientProcess.MainWindowHandle, ClientContainer.Handle)
SendMessage(ClientProcess.MainWindowHandle, WM_SYSCOMMAND, SC_MAXIMIZE, 0)

End If

SetChildTimer.Enabled = False
End Sub

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This will set notepad as the child of the vb.net form once the timer has ticked.

This is a sample picture: https://i-msdn.sec.s-msft.com/dynimg/IC118780.gif
(from MSDN- not malicious)
So, although the child form is embedded and has become part of the parent application, it still remains an external process. It confines to the forms borders, but does not become an actual element of the form and, therefore, the code that you kindly posted will not work.

Thanks!

PS: If you need to know the name of the process when helping me with the code, it's handle is "WPS Spreadsheets (32 bit)" and it's process name is "et.exe"

Hello, sorry for my late reply, I don't expect you to reply to this promptly either xD. The timer method does capture the mouse click. If you look at the code, it captures all mouse clicks, not only the ones that occur inside my form, but also outside of the form. The problem is, each time the timer ticks (every 50ms or so), the mouse click is recorded - so it records the actual time in which to click is held down, I don't want it to do that, I want it to record the actual event of clicking, that way only a single "10000" is returned to the listbox. Some, in capturing the mouse clicks [essentially] the method works, it just needs honing - it must only capture the action of clicking once.