WindowsOpening and WindowsOpened events on DockSite do not take effect.

I subscribe to the event on DockSite directly by the following code.

this.Content.dockSite.WindowsOpening += this.DockSite_WindowsOpening;
this.Content.dockSite.WindowsOpened += this.DockSite_WindowsOpened;
this.Content.dockSite.WindowsClosed += this.DockSite_WindowsClosed;
this.Content.dockSite.WindowsClosing += this.DockSite_WindowsClosing;

Then I create a ToolWindow and call the Open method to open it:

var window = new ToolWindow(this.Content.dockSite);
window.Open();

At this time, the Open-related events are not triggered, but the Close-related events are triggered when the ToolWindow is closed.

What could be the reason for this please? Our scene is not using MVVM way.