hello, I have a question about Flutter navigator/MaterialPageRoute , please help me : I have a BUTTON ,here is some code:  
[enter image description here][1]


and i got the error like this:[enter image description here][2]


i never met the error like this, but when i add the 'dynamic' like this:[enter image description here][3]


  [1]: https://i.stack.imgur.com/meoic.png
  [2]: https://i.stack.imgur.com/0o4aD.png
  [3]: https://i.stack.imgur.com/0UXkO.png

i am so confusing ! plz help !