Nav Mesh Agent Find Stopping Distance

Hello Everybody , It's like a problem adding a trigger to player so when enemy gets into that then it will play attack animation , but what if it will make a little distance like player is walking and enemy is following and in a very short distance it's getting a problem like trigger in/out every short time and the enemy is never playing single animation simultaneously, Enemy is like playing half run and half attack animation , That's why i need help to know how to write code about - if enemy will reach stoping distance in nav mesh agent built-in function ,then it will play attack animation . please make it simple , thanks .