Cannot programmically press button, getting a WM_MOUSELEAVE after WM_LBUTTONDOWN

I am trying to press a graphical button that does not have a HWND. I have the following code:

        Dim MousePos As Long = MakeDWord(clientPoint.X, clientPoint.Y)
        Dim iDownResult As Long = SendMessage(wndHandle, WM_LBUTTONDOWN, MK_LBUTTON, MousePos)
        Dim iUpResult As Long = SendMessage(wndHandle, WM_LBUTTONUP, MK_LBUTTON, MousePos)

However the button is not actually being pressed. The button graphic changes to the "pressed down" graphic, but the expected action from the button being pressed does not occur. Checking the window with SPY++ running shows that the messages are being received with correct arguments, however a "WM_MOUSELEAVE" is occurring after both SendMessages. The windows are active, have focus, and are on top of the screen.

When I test it by pressing the button manually there is no "WM_MOUSELEAVE".

How can I get past this and have the button actually press.

Thanks
tolvorAsked:
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Reece CottamConnect With a Mentor Freelance Web Developer and DesignerCommented:
Have you tried the SendInput method instead of SendMessage?

Like this;

 public class ClickOnPointTool
  {

    [DllImport("user32.dll")]
    static extern bool ClientToScreen(IntPtr hWnd, ref Point lpPoint);

    [DllImport("user32.dll")]
    internal static extern uint SendInput(uint nInputs, [MarshalAs(UnmanagedType.LPArray), In] INPUT[] pInputs,  int cbSize);

#pragma warning disable 649
    internal struct INPUT
    {
      public UInt32 Type;
      public MOUSEKEYBDHARDWAREINPUT Data;
    }

    [StructLayout(LayoutKind.Explicit)]
    internal struct MOUSEKEYBDHARDWAREINPUT
    {
      [FieldOffset(0)]
      public MOUSEINPUT Mouse;
    }

    internal struct MOUSEINPUT
    {
      public Int32 X;
      public Int32 Y;
      public UInt32 MouseData;
      public UInt32 Flags;
      public UInt32 Time;
      public IntPtr ExtraInfo;
    }


    public static void ClickOnPoint(IntPtr wndHandle , Point clientPoint)
    {
      var oldPos = Cursor.Position;

      /// get screen coordinates
      ClientToScreen(wndHandle, ref clientPoint);

      /// set cursor on coords, and press mouse
      Cursor.Position = new Point(clientPoint.X, clientPoint.Y);

      var inputMouseDown = new INPUT();
      inputMouseDown.Type = 0; /// input type mouse
      inputMouseDown.Data.Mouse.Flags = 0x0002; /// left button down

      var inputMouseUp = new INPUT();
      inputMouseUp.Type = 0; /// input type mouse
      inputMouseUp.Data.Mouse.Flags = 0x0004; /// left button up

      var inputs = new INPUT[] { inputMouseDown, inputMouseUp };
      SendInput((uint)inputs.Length, inputs, Marshal.SizeOf(typeof(INPUT)));

      /// return mouse
      Cursor.Position = oldPos;
    }

  }
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Reece CottamFreelance Web Developer and DesignerCommented:
If this is in VB.NET, why not fire off a custom event instead of using messages?

It seems like you're making this very complicated by doing it that way, is there a reason you're doing that?
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tolvorAuthor Commented:
The button is in another application that I don't have access to the code. I want my application to send mouse clicks to keep another application active.
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Reece CottamFreelance Web Developer and DesignerCommented:
and this is in Winforms I presume?
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tolvorAuthor Commented:
Yes, this is a WinForms based application, using vb.net, Visual Studio 2013, on a Windows 10 platform.
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Reece CottamFreelance Web Developer and DesignerCommented:
Also, are you triggering the button up? if you leave it down then the event won't fire
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tolvorAuthor Commented:
It works. Many thanks  :-)
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