Custom widget doesn't show - flutter

Question

I'am trying to create a custom widget CarteSim and I'am trying to call it everytime I click on Floating Action Button , but unfortunately it doesn't show when I call it inside the button , but it shows when I call it in the Scaffold , please who has ever experience that
here s my code
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.pink,
title: Text(" INWI "),
),
body: SingleChildScrollView(
child: Container(
child: Center(
child: Column(
children: <Widget>[
DropdownButton<String>(
items: _type.map((String dropDownStringItem) {
return DropdownMenuItem<String>(
value: dropDownStringItem,
child: Text(dropDownStringItem),
);
}).toList(),
onChanged: (String newValueSelected) {
setState(() {
this._currentItemSelected = newValueSelected;
});
},
value: _currentItemSelected,
),
Divider(
color: Colors.black,
),
new Row(
children: [
new Text(" type client supporte * carte avec 1 cin"),
new Checkbox(value: _isChecked, onChanged: (bool value){ onChanged(value);}),
]
),
Divider(
color: Colors.black,
),
new Column(
children: <Widget>[
CarteCin(),
CarteSim(),
]
)
],
),
),
)
),
floatingActionButton: FloatingActionButton(
onPressed: (){
Column(
children: <Widget>[
CarteSim(),
]
);
},
child: Icon(Icons.add),
backgroundColor: Colors.pink,
),
);
}
]
}

Answer 1

you are misunderstanding the process. The onPressed key actually used for call actions on press the floatingActionButton. You can write functions there, like you can update your state or print anything on your console or call an API to get data. But you can't display any widget from there.
Now what you're trying to do, that can be resolved like this. Whenever you press that button you should update your state, i.e bool show. Then modify your Column children based on that show state.

Answer 2

Here is an example how tu update the UI in flutter
class FrontPage extends StatefulWidget {
#override
_FrontPageState createState() => _FrontPageState();
}
class _FrontPageState extends State<FrontPage> {
bool currentStateShowsThis;
initState() {
currentStateShowsThis = false;
super.initState();
}
Widget build(BuildContext context) {
final color = currentStateShowsThis ? Colors.blue : Colors.red;
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.pink,
title: Text(" INWI "),
),
body: SingleChildScrollView(
child: Container(
child: Center(
child: Column(
children: <Widget>[
Container(width: 100, height: 100, color: color,) // alternatively you can change the widgets being displayed
],
),
),
)
),
floatingActionButton: FloatingActionButton(
onPressed: (){
setState(() {
currentStateShowsThis = !currentStateShowsThis;
});
},
child: Icon(Icons.add),
backgroundColor: Colors.pink,
),
);
}
}
In your example "the button" will call back the
onPressed:
Which will only create the widgets in that method (Column ...) and not place them in a the layout.