setState() or markNeedsBuild called during build

In my case I was calling the setState method before the build method had completed the process of building the widgets.

You can face this error if you are showing a snackBar or an alertDialog before the completion of the build method, as well as in many other cases. So, in such cases you should use a call back function as shown below:

WidgetsBinding.instance.addPostFrameCallback((_){  // Add Your Code here.});

or you can also use SchedulerBinding which does the same:

SchedulerBinding.instance.addPostFrameCallback((_) {  // add your code here.  Navigator.push(        context,        new MaterialPageRoute(            builder: (context) => NextPage()));});

Your code

onPressed: buildlist('button'+index.toString()),

executes buildlist() and passes the result to onPressed, but that is not the desired behavior.

It should be

onPressed: () => buildlist('button'+index.toString()),

This way a function (closure) is passed to onPressed, that when executed, calls buildlist()

I was also setting the state during build, so, I deferred it to the next tick and it worked.

previously

myFunction()

New

Future.delayed(Duration.zero, () async {  myFunction();});