Version: 2018.1
public static int hotControl ;

説明

現在有効なコントロール ID

The hot control is one that is temporarily active. When the user mousedown's on a button, it becomes hot.
No other controls are allowed to respond to mouse events while some other control is hot.
once the user mouseup's, the control sets hotControl to 0 in order to indicate that other controls can now respond to user input.

no example available in C#