Add Widget based on Condition - dart

Question

I want to add a MaterialButton in a widget's build method only if some condition is true. For instance:
if (..) {
MaterialButton(..)
}
How do I achieve this in Flutter?

Answer 1

It is very simple using conditional operators:
build(context) => condition ? MaterialButton(...) : Container();
In this case, condition is a boolean expression (returning bool, same thing you would put into an if-statement) and the empty Container will render as empty space and will not take up any space.

Answer 2

Yes actually I see at least two ways of doing it.
The first one is :
Container(
child: your_test_here ? MaterialButton() : Container(height:0), //or any other widget but not null
)
The other way of doing it is by creating a function:
Widget your_test_widget(){
if (your_test_here){
return MaterialButton();
}
else{
return Container(height:0); //or any other widget but not null
}
}
Call it in your tree :
Container(
child:your_test_widget(),
)
Hope it helps !!

Answer 3

Another option if your widget appears in a List<Widget>/<Widget>[] (i.e. with Row, Column or ListView), you can do something like:
#override
Widget build(BuildContext context) => Column(children: _buildChildren());
List<Widget> _buildChildren() {
var list = [/* put widgets that always show at top here */];
if(myCondition) list.add(MyConditionalWidget());
return list;
}

Answer 4

It's a nice question!
Assuming you want to add your button in a Container you can do the following:
Container (
child: MyWidget()
)
Widget MyWidget() {
if (...) {
return new MaterialButton(
...
)
}
return Container();
}
Obviously here adding in the Container is an example, you can assign a method that returns a Widget to every child elements!
A more explicative example:
class Example extends StatefulWidget {
// code
#override
EventPageState createState() => ExampleState();
}
class ExampleState extends State<Example> {
#override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
Text("Static Widget")
CustomDynamicWidget(),
],
),
)
}
Widget CustomDynamicWidget() {
if (...) {
return new Text("Dynamic Widget IF block")
} else if (...) {
return new Text("Dynamic Widget ELSE IF block")
}
return Container();
}
}