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public static IntPtr GetHwndsForUWPApp(string aumid) {
    NativeHWNDExtractor.aumid = aumid;
    ENUMWINDOWPARAM ep = new ENUMWINDOWPARAM();
    IntPtr eplParam = Marshal.AllocHGlobal(Marshal.SizeOf(ep));
    Marshal.StructureToPtr(ep, eplParam, false);

    NativeMethods.EnumWindows(new NativeMethods.WNDENUMPROCR(CheckWindowUWP), ref eplParam);

    object obj = Marshal.PtrToStructure(eplParam, typeof(ENUMWINDOWPARAM));
    ENUMWINDOWPARAM newep = (ENUMWINDOWPARAM)obj;
    Marshal.FreeHGlobal(eplParam);

    return new IntPtr(newep.ihWnd);
}

private static bool CheckWindowUWP(IntPtr hwnd, ref IntPtr lParam) {
    ENUMWINDOWPARAM ep = (ENUMWINDOWPARAM)Marshal.PtrToStructure(lParam, typeof(ENUMWINDOWPARAM));
    
    StringBuilder sbClassName = new StringBuilder(256);
    NativeMethods.GetClassName(hwnd, sbClassName, sbClassName.Capacity);
    string className = sbClassName.ToString();

    if (className.Equals("ApplicationFrameWindow")) {
        // get real hWnd
        NativeInterfaces.IPropertyStore pPropertyStore;
        Guid guid = new Guid("{886D8EEB-8CF2-4446-8D02-CDBA1DBDCF99}");
        NativeEnums.HRESULT hr = NativeMethods.SHGetPropertyStoreForWindow(hwnd, ref guid, out pPropertyStore);
        if (hr == NativeEnums.HRESULT.S_OK) {
            NativeStructs.PROPVARIANT propVar = new NativeStructs.PROPVARIANT();
            hr = pPropertyStore.GetValue(ref NativeDefinitions.PKEY_AppUserModel_ID, out propVar);
            string sAUMID = Marshal.PtrToStringUni(propVar.pwszVal);
            if (sAUMID != null && sAUMID.Equals(aumid)) {
                ep.ihWnd = hwnd.ToInt32();
                Marshal.StructureToPtr(ep, lParam, false);
                Marshal.ReleaseComObject(pPropertyStore);
                return false;
            }
            Marshal.ReleaseComObject(pPropertyStore);
        }
    }

    return true;
}