Thanks for your reply. I’ve tried as you said. Create a new UserWidget and added a SizeBox with IsVariable checked. But there is no blueprint node available for SizeBox class about setting Tool Tip Widget. Another thing I metioned is, when I scroll down the Detail panel about to Tool Tip Widget option at the first time, the IDE will hit break point at following line.
if ( !ensure(bIsEditable && bDoSignaturesMatch) )
DetailWidgetExtensionHandler.cpp Line: 61
Seems there are some logical issue about current version of engine. And caused the Tool Tip Widget option is unavailable now.