当键盘出现时，我的整个小部件树会重建吗？

Question

I am trying to build a responsive mobile app so I found an approach were i would divide the sreen into definite number of grids and get the grid width and height and then use this width and height to size my widgets

Question :

I would definitly get my screen's size from MediaQuery.of(context) but since i will only use it once to do my calculations will my widget tree rebuild (assuming i did this calculation in my root widget) whenever a keyboard appears or not? And if it will rebuild should i do the calculations in a different place?

Answer 1

No, if you didn't place any set state or callback during that rebuild the widget when you open the keyboard. However, the issue can be easily resolved by putting your main widget "below" the Scaffold in a SingleChildScrollView to avoid rendering issues.

If you absolutely need to perform actions when the keyboard appears you can use a FocusNode in the textField and add a listener to it with the addListener method. By passing a function to add Listener, you can trigger a setState every time you need, causing the widget to rebuild with the new parameters.

This is a very simplified version of what I mean:

class MyWidget extends StatefulWidget{
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {

  FocusNode _focusNode;
  int state=0;

  @override
  Widget build(BuildContext context) {
    return Container(
      height: state==0?100:200, //change the height depending on "state"
      child: TextField(
        focusNode: _focusNode,
      ),
    );
  }

  void onFocus(){
    setState(() {
      //Check if the focus node is focused
      if(_focusNode.hasFocus) state=1; //Change the value of the state
    });
  }

  @override
  void initState() {
    super.initState();
    _focusNode=FocusNode();
    _focusNode.addListener(onFocus); //Here on focus will be called
  }

  @override
  void dispose() {
    super.dispose();
    _focusNode.dispose();
  }
}