How to immediately get the size of a Widget created at runtime?

What’s the best way to get the Size of a Widget? If it is runtime and the Widget construction is added to the PanelWidget(A widget that can accommodate widget), I found that its LocalSize() changes like this. After a total of 3 ticks, 0->defaultSize->correct size according to the size of the correct content.
If it’s a Widget added to a PanelWidget at non-runtime, I can use ForcePrepass() to get it’s correct size immediately.
I want to know how to immediately get the size of a Widget constructed at runtime?
Thanks!