title: how to find performance issue and fix in flutter
body: <p>I am using dart to develop a flutter(version 1.22.5) app, in my Android Studio(version 4.1.2), I found some frame render very slow(60 frame/s is good, now only 1/2) like this:</p>
  <p><a href="https://i.stack.imgur.com/lGubg.png" rel="noreferrer"><img src="https://i.stack.imgur.com/lGubg.png" alt="enter image description here" /></a></p>
  <p>but the problem is, I do not know where make the render slow, how to find the performance issue? I know it slow, but where? what should I do to find it out? Is there any tips?</p>