Odtnhj

Flutter app create a Widget List (wList) and show screen properly. If user presses a button it will add a divider() to the wList and update the screen by setState(). However, the screen didn't update. I think I may not understand well the logic of setState. If I update the wList and call the setState() function, I think it should update the screen. But It didn't.

 @override
 Widget build(BuildContext context) 
 return Scaffold(
 backgroundColor: Colors.white,
 appBar: AppBar(
 title: Text('檯號： $widget.inputTableNumber'),
 centerTitle: true,
 backgroundColor: Colors.black,
 actions: <Widget>[
 IconButton(icon: Icon(Icons.edit), onPressed: () => _showButtons(), color: Colors.white,)
 ],
 ),
 body: RepaintBoundary(
 key: _renderInvoice,
 child: Padding(
 padding: EdgeInsets.all(15.0),
 child: ListView(
 children: wList,
 ),
 )
 )
 );
 

 _showButtons() 
 showModalBottomSheet<void>(
 context: context,
 builder: (BuildContext context) 
 return Container(
 color: Colors.white54,
 height: 500.0,
 child: GridView.count(
 primary: false,
 padding: const EdgeInsets.all(20.0),
 crossAxisSpacing: 30.0,
 mainAxisSpacing: 30.0,
 crossAxisCount: 3,
 children: <Widget>[
 FloatingActionButton(
 onPressed: () _addPercentage(0.1);,
 heroTag: null,
 backgroundColor: Colors.purpleAccent,
 child: Text('+10%', style: TextStyle(fontSize: 20.0, fontWeight: FontWeight.w500)),
 foregroundColor: Colors.black,
 ),

 ],
 )
 );
 );
 

 _addPercentage(double d) 
 Navigator.pop(context);
 setState(() 
 wList.add(Divider(color: Colors.black,));
 );
 

So the reason this fails is because the standard Listview constructor expects a const children parameter. Obviously, your wList is not a const value and changes when your button is pressed.

Instead, you should use Listview.builder like this:

ListView.builder(
 itemCount: wList.length,
 itemBuilder: (context, index) 
 return wList[index];
 
 )