slint-ui/slint · error

C++: NativeWindowHandle created with null hwnd

Error message

C++: NativeWindowHandle created with null hwnd

What it means

Error "C++: NativeWindowHandle created with null hwnd" thrown in slint-ui/slint.

Source

Thrown at api/cpp/platform.rs:794

    struct CppRawHandle(Arc<RawHandlePair>);

    impl From<(RawWindowHandle, RawDisplayHandle)> for CppRawHandle {
        fn from(pair: (RawWindowHandle, RawDisplayHandle)) -> Self {
            Self(Arc::new(RawHandlePair(pair)))
        }
    }

    type CppRawHandleOpaque = *const c_void;

    #[unsafe(no_mangle)]
    pub unsafe extern "C" fn slint_new_raw_window_handle_win32(
        hwnd: *mut c_void,
        _hinstance: *mut c_void,
    ) -> CppRawHandleOpaque {
        let handle = CppRawHandle::from((
            RawWindowHandle::Win32(raw_window_handle::Win32WindowHandle::new(
                (hwnd as isize).try_into().expect("C++: NativeWindowHandle created with null hwnd"),
            )),
            RawDisplayHandle::Windows(raw_window_handle::WindowsDisplayHandle::new()),
        ));
        Box::into_raw(Box::new(handle)) as CppRawHandleOpaque
    }

    #[unsafe(no_mangle)]
    pub unsafe extern "C" fn slint_new_raw_window_handle_x11_xcb(
        window: u32,
        visual_id: u32,
        connection: *mut c_void,
        screen: core::ffi::c_int,
    ) -> CppRawHandleOpaque {
        use raw_window_handle::{XcbDisplayHandle, XcbWindowHandle};
        let handle = CppRawHandle::from((
            RawWindowHandle::Xcb({
                let mut hnd = XcbWindowHandle::new(
                    window

View on GitHub (pinned to 3fd8f2ec03)

Solutions

1. Do not create a NativeWindowHandle with a null HWND on Windows.
2. Obtain a valid window handle before calling.

When it happens

Trigger: Thrown at api/cpp/platform.rs:794 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of slint-ui/slint@3fd8f2ec03 (2026-08-19). Data as JSON: /api/errors/64c20f9cb5528785. Report an issue: GitHub.