我在使用UIKitDynamics时总是遇到崩溃。它不会在每次代码运行时发生，但它经常发生。有人遇到过这个吗？Assertionfailed:(a.x>=0.0f&&a.y>=0.0f),functionSolveVelocityConstraints,file/SourceCache/PhysicsKit/PhysicsKit-4.6/PhysicsKit/Box2D/Dynamics/Contacts/b2ContactSolver.cpp,line422.这是产生错误的代码。我猜测它与碰撞边界有关。UIDynamicAnimator*animator=[[UIDynamicAni