如何使用Swift在FireBase DataBase中进行更改时获取Count值？

I am new to swift Programming and FireBase,I have Implemented Chat Application,Which I stored the Message Count using sender and Receiver ID ,In receiver side getting count Perfectly,But when new count is added in FireBase I want to get that new count, for that I used timer to call a function every 10 seconds,i am getting count perfectly ,But My problem is Timer running continuously, App getting Hang and slow,After sometimes I doesn't response, can anyone suggest me how to call the function every 10 seconds or how to use timer.I am new to swift Programming and FireBase,I ha