Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to activate constraint with anchors <NSLayoutYAxisAnchor:0x6000021743c0 "UITableView:0x7fb06a2b0200.top"> and <NSLayoutYAxisAnchor:0x600002174780 "HDWPigeonPlatform.TabBarLineView:0x7fb0695d3b00.bottom"> because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal.'
當(dāng)A視圖添加在父視圖上,B視圖未添加在父視圖上時,而A視圖引用了B視圖,找不到B視圖的父視圖,也就是說沒有一個固定的錨點,沒有一個相對約束,從而報錯