Why does get_CurrentNativeWindowHandle return 0 in some cases?

Question

Why does get_CurrentNativeWindowHandle return 0 in some cases?

Gaurang Tandon 20

I am using a focus change handler to track change of focus across all applications on Windows. When I focus into the following textbox in Chrome on an empty HTML page:

<textarea></textarea>

The value of window handle I obtain is 0. I am using the following code to implement the focus change handler: https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src/WinAuto/uiauto-howto-implement-event-handlers.md#handling-focus-changed-events

I made the following change to get the window handle and print it:


    HRESULT STDMETHODCALLTYPE
    HandleFocusChangedEvent(IUIAutomationElement *pSender) {
        _eventCount++;
        UIA_HWND windowHandle;
        HRESULT hr = pSender->get_CurrentNativeWindowHandle(&windowHandle);
        if (SUCCEEDED(hr)) {
            HWND hwnd = (HWND)windowHandle;
            // this value is printed as 0
        }
        return S_OK;
    }

Any suggestion on how to get the correct window handle in this case? The documentation (https://learn.microsoft.com/en-us/windows/win32/api/uiautomationclient/nf-uiautomationclient-iuiautomationelement-get_currentnativewindowhandle) does not specify any reasons as to why this could be 0.

Gaurang Tandon 20 Reputation points

2024-03-01T11:45:12.2133333+00:00

Thanks @RLWA32 I have used inspect.exe to verify that the focused automation element does not have an HWND. Any idea why that would be? Do we need to generate it somehow? The documentation does not make it clear that this property could be missing.
RLWA32 52,571 Reputation points

2024-03-01T12:35:31.3+00:00

@Gaurang Tandon I converted my prior comment to an Answer that can be accepted.

There are various frameworks available for creating user interfaces and their elements. Not every framework uses the Windows API (e.g. CreateWindowEx function) to create those elements (windows/controls). For example, a WPF textbox control does not have an HWND. That is why an HWND may not always be available for an automation element.
Gaurang Tandon 20 Reputation points

2024-03-01T12:52:59.85+00:00

Thanks @RLWA32 I accepted your answer. One follow up question: is there any other direct way to get the window handle given the automation element? One way seems to be to iterate all the way upto the root document, and get the window handle from there. But it is expensive I feel. Any suggestions on this?
RLWA32 52,571 Reputation points

2024-03-01T13:10:28.36+00:00

is there any other direct way to get the window handle given the automation element?

If the automation element passed to the focus change event handler does not have a native window handle then there is nothing to get. So I don't understand what you are asking.
Gaurang Tandon 20 Reputation points

2024-03-01T13:13:55.3266667+00:00

Sure I will clarify @RLWA32 The automation element is a part of a window on Windows. So, I need to get the handle of that window. For example: I am getting HWND as 0 in a textbox element in a Chrome window. In that case, I would like to get the window handle of the Chrome window (which is the window to which the textbox element belongs).
RLWA32 52,571 Reputation points

2024-03-01T13:34:40.7666667+00:00

Have a look here - https://learn.microsoft.com/en-us/archive/blogs/winuiautomation/finding-the-handle-of-the-window-that-contains-a-ui-automation-element

Answer accepted by question author

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Gaurang Tandon 20 Reputation points

2024-03-01T11:45:12.2133333+00:00

Thanks @RLWA32 I have used inspect.exe to verify that the focused automation element does not have an HWND. Any idea why that would be? Do we need to generate it somehow? The documentation does not make it clear that this property could be missing.
RLWA32 52,571 Reputation points

2024-03-01T12:35:31.3+00:00

@Gaurang Tandon I converted my prior comment to an Answer that can be accepted.

There are various frameworks available for creating user interfaces and their elements. Not every framework uses the Windows API (e.g. CreateWindowEx function) to create those elements (windows/controls). For example, a WPF textbox control does not have an HWND. That is why an HWND may not always be available for an automation element.
Gaurang Tandon 20 Reputation points

2024-03-01T12:52:59.85+00:00

Thanks @RLWA32 I accepted your answer. One follow up question: is there any other direct way to get the window handle given the automation element? One way seems to be to iterate all the way upto the root document, and get the window handle from there. But it is expensive I feel. Any suggestions on this?
RLWA32 52,571 Reputation points

2024-03-01T13:10:28.36+00:00

is there any other direct way to get the window handle given the automation element?

If the automation element passed to the focus change event handler does not have a native window handle then there is nothing to get. So I don't understand what you are asking.
Gaurang Tandon 20 Reputation points

2024-03-01T13:13:55.3266667+00:00

Sure I will clarify @RLWA32 The automation element is a part of a window on Windows. So, I need to get the handle of that window. For example: I am getting HWND as 0 in a textbox element in a Chrome window. In that case, I would like to get the window handle of the Chrome window (which is the window to which the textbox element belongs).
RLWA32 52,571 Reputation points

2024-03-01T13:34:40.7666667+00:00

Have a look here - https://learn.microsoft.com/en-us/archive/blogs/winuiautomation/finding-the-handle-of-the-window-that-contains-a-ui-automation-element

Answer 1

RLWA32 52,571

Maybe the automation element does not have a native window handle. Have you used inspect.exe to verify that the focus window does have an HWND?

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Why does get_CurrentNativeWindowHandle return 0 in some cases?

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