iOS aulayout NSGenericException

Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to install constraint on view.Does the constraint reference something from outside the subtree of the view?That's illegal. constraint: view:>'

*** First throw call stack:

(0x1885a61c0 0x186fe055c 0x1885a6108 0x188fd592c 0x18e4fdb1c 0x18e4fd8e4 0x18e4fd8a4 0x1005ae218 0x1005ad2e8 0x1005ac628 0x18e4010b0 0x18e4baca0 0x18e4bab78 0x18e4b9ec0 0x18e4b990c 0x18e4b94c0 0x18e4b9424 0x18e3fe220 0x18b8be188 0x18b8b2e64 0x18b8b2d24 0x18b82f7ec 0x18b856c58 0x18b857678 0x1885537dc 0x18855140c 0x188480068 0x18e46c2b0 0x18e467034 0x100536c74 0x1874645b8)

解决：

错误：[secondeScrollDiskViewaddConstraint:leftConstraint];

正确：leftConstraint.active=YES;