Question

I don’t fully understand these topics.

I work with several WinAPI methods

public delegate bool Win32Callback(IntPtr hwnd, ref IntPtr lParam);

[DllImport("user32.Dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool EnumChildWindows(IntPtr parentHandle, Win32Callback callback, IntPtr lParam);

and

public static bool BrowserEnumChildrenCallback(IntPtr hWnd, ref IntPtr lParam)
{
    if (hWndMeetsConditions)
        return true;
    //code
    return false;
}

Is it possible get hWnd for which was returned true from BrowserEnumChildrenCallback?

Win32Callback callBack = new MainWindow.Win32Callback(BrowserEnumChildrenCallback);
if (EnumChildWindows(hWnd, callBack, hWnd))
{
    //here
}

Answer 1

Several problems:

• The delegate declaration is wrong, the last argument is IntPtr, not ref IntPtr.
• The callback should return true to continue iterating, you’re doing it backwards
• Write GC.KeepAlive(callBack) after the EnumChildWindows() call to prevent the delegate object from getting garbage collected.
• Don’t use the return value of EnumChildWindows(), the SDK docs note that it is unused. You detect failure by not finding the window.

Answering the actual question: store the window handle in a field of your class. Thus:

private IntPtr windowFound;

private void iterateChildWindows(IntPtr parent) {
    windowFound = IntPtr.Zero;
    var callBack = new MainWindow.Win32Callback(BrowserEnumChildrenCallback);
    EnumChildWindows(parent, callBack, IntPtr.Zero);
    GC.KeepAlive(callBack);
    if (windowFound != IntPtr.Zero) {
       // etc..
    }
}

private bool BrowserEnumChildrenCallback(IntPtr hWnd, IntPtr lParam)
{
    if (hWndMeetsConditions(hWnd)) {
        windowFound = hWnd;
        return false;
    }
    return true;
}

A lambda works well too.