How I can view FloatingActionButton on condition - flutter

Question

I have list of orders orderList. If that isEmpty, FloatingActionButton is hide. In case orderList have products - FAB will be shown. My code:
bool statusFAB = false;
_getFABState(){
setState(() {
if(!orderList.isEmpty){
statusFAB = true;
}
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: _getFAB(),
backgroundColor: _kAppBackgroundColor,
body: Builder(
builder: _buildBody,
),
);
Widget _getFAB() {
if(statusFAB){
return FloatingActionButton(
backgroundColor: Colors.deepOrange[800],
child: Icon(Icons.add_shopping_cart),
onPressed: null);
}
}
It's not working, because condition work once, but state of orderList can be change anytime.

Answer 1

You don't need to store the statusFAB variable, you can just evaluate it on the fly. See updated sample below:
#override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: _getFAB(),
backgroundColor: _kAppBackgroundColor,
body: Builder(
builder: _buildBody,
),
);
Widget _getFAB() {
if (orderList.isEmpty) {
return Container();
} else {
return FloatingActionButton(
backgroundColor: Colors.deepOrange[800],
child: Icon(Icons.add_shopping_cart),
onPressed: null);
}
}

Answer 2

Well there is a shortcut which can be used with the ternary operator and can be used within Scaffold of a Stateful Widget as
floatingActionButton: orderList.isEmpty ? Container() : FloatingActionButton(...)
Unless you need a long and complicated function, this works fine. Even if you need a complicated function, then that function can be called only when the drawing was needed
floatingActionButton: orderList.isEmpty ? Container() : ComplicatedFn(...)
Widget ComplicatedFn() {
//.... Complicated Algo
return FloatingActionButton(...)
}

Answer 3

import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List<Product> orderList = List();
int counter = 0;
void getCount(){
setState(() {
counter = orderList.length;
});
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: Center(
child: Container(
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
IconButton(
onPressed: (){
if(orderList.isNotEmpty)
orderList.removeLast();
getCount();
},
icon: Icon(Icons.remove),
color: Colors.red,
),
Text('$counter'),
IconButton(
onPressed: (){
orderList.add(Product('product'));
getCount();
print('product added');
},
icon: Icon(Icons.add),
color: Colors.blue,
)
],
),
),
),
floatingActionButton: _getFAB()
);
}
Widget _getFAB() {
if (orderList.isEmpty) {
return Container();
} else {
return FloatingActionButton(
backgroundColor: Colors.deepOrange[800],
child: Icon(Icons.shopping_cart),
onPressed: null);
} }
}
class Product {
String title;
Product(this.title);
}