Check out example codes for "c# postmessage mouse click". It will help you in understanding the concepts better.

Code Example 1

[DllImport("user32.dll")]
static extern bool PostMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

const int WM_LBUTTONDOWN = 0x0201;
const int WM_LBUTTONUP = 0x0202;

PostMessage(hWnd, WM_LBUTTONDOWN, 1, 0);
PostMessage(hWnd, WM_LBUTTONUP, 0, 0);

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