In UIToolkit, button's click event is not invoked, perhaps due to parent's event?

Unity Engine
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1

I wanna create a drag scroll bar. so I add a scrollbar, and register MouseUpEvent, MouseDownEvent, MouseMoveEvent to this scrollbar in its construction function, that copied from here [Preformatted text](https://discussions.unity.com/t/scrollview-with-drag-scrolling/861606/21)
The matter is that I add Button to this scroll, and when I click it ,it wouldn’t react to click.
I tried to delete StopPropagation, so that event can get to the button, but it did not help.

2

Here is how I create the Button, and when I click, it never log the message.
By the way,the MouseDownEvent can work normally,while MouseUpEvent and its own button clicked event cannot work

     for (var i = 0; i < 15; ++i)
        {
            var bt = new Button((() =>
            {
                Debug.Log("Click Up");
            }))
            {
                name = "Bt" + i,
                text = "Bt" + i,
                style =
                {
                    left=5,
                    width = 40,
                    height = 40,
                    backgroundColor = (Color)new Color32(56, 56, 56, 255)
                }
            };

            
            //Only useTrickleDown.TrickleDown, can get this event during trickledown
            bt.RegisterCallback<MouseDownEvent>(m_MenuScroll.ExternMouseDown,TrickleDown.TrickleDown);
            bt.RegisterCallback<MouseUpEvent>(m_MenuScroll.ExternMouseUp,TrickleDown.TrickleDown);
 m_MenuScroll.Add(bt);
}
4

MouseEvents are backward-compatibility events that are superseded by PointerEvents, try using PointerUpEvent instead