Get scrolling direction of another window/application

Question

I want to detect the scrolling direction of another application. I am able to do so if the user scrolls through Mouse Wheel or Keyboard (Up/Down/Left/Right keys) through hooks. But I am not able to capture the same when the user uses the scrollbars present on the applications like Chrome.

I've tried below native method, but it does not work for many applications like chrome and works for Notepad++, as it is not able to detect scroll bars for chrome. I want something that works for all the applications.

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetScrollInfo(IntPtr hwnd, int fnBar, ref SCROLLINFO lpsi);

I have quite a bit of research but could not find anything that could give me the directions in which the page is scrolling. Please let me know if any further information is required.

Update:

I am trying to use UI Automation to get the scroll bar information for Chrome.

Here's how?

I have made a collection of windows Gui Rectangles using EnumChildWindows, which retrieved child controls as well. Based upon the mouse position, have selected the window handle whose Gui Rectangle contains my mouse position. The handle I obtained had the Gui Rectangle = chrome's client area.

Problem:

Below is the code. And it gives me an empty collection in elementCollection in case of Chrome and successfully returns 2 scroll bar elements in case of Notepad++.

var element = AutomationElement.FromHandle(handle);
if(element != null)
{
    Condition condition = 
       new PropertyCondition(AutomationElement.ControlTypeProperty, ControlType.ScrollBar);

    // Find all children that match the specified conditions.
    AutomationElementCollection elementCollection =
        element.FindAll(TreeScope.SubTree, condition);
 }

Answer 1

What you need to do is call the GetScrollInfo method twice and compare those values to find out; whether the control is being scrolled and to calculate (previous < current) the direction. You need to repeat this process as long as you want to keep monitoring the scrolling direction.

Now you should create some kind of worker class to handle things nicely, for the purpose of this question I've used a simple Console application that polls the SCROLLINFO structure of the handle using a while-loop:

static void Main(string[] args)
{
    var handle = (IntPtr)0x35087C; // notepad textbox handle

    var prevInfo = default(SCROLLINFO);
    int iterations = 1000;

    while (iterations > 0)
    {
        var curInfo = new SCROLLINFO();
        curInfo.cbSize = Marshal.SizeOf(curInfo);
        curInfo.fMask = (int)ScrollInfoMask.SIF_ALL;

        if (GetScrollInfo(handle, (int)ScrollBarDirection.SB_VERT, ref curInfo))
        {
            var dir = curInfo.nPos < prevInfo.nPos ? "Up" : "Down";
            dir = curInfo.nPos == prevInfo.nPos ? "Unchanged" : dir;

            Console.WriteLine(dir);

            prevInfo = curInfo;
        }
        else
        {
            Console.WriteLine($"No scrolling.. {Marshal.GetLastWin32Error()}");
        }

        System.Threading.Thread.Sleep(100);
        iterations--;
    }

    Console.ReadLine();
}

Note that the handle variable contains the pointer to the textbox of a notepad process (which is NOT the same as the handle to the notepad process). I've used WinSpy++ to retrieve the handle from the notepad process.

I've used the GetScrollInfo MSDN page to read about the API call itself, GetScrollInfo Pinvoke.NET page to obtain all the required structs/enums.