How to use conditional statement within child attribute of a Flutter Widget (Center Widget)

So far whenever I needed to use a conditional statement within a Widget I have done the following (Using Center and Containers as simplified dummy examples):

new Center(
  child: condition == true ? new Container() : new Container()
)

Though when I tried using an if/else statement it would lead to an Dead code warning:

new Center(
  child: 
    if(condition == true){
      new Container();
    }else{
      new Container();
    }
)

Interestingly enough I tried with a switch case statement and it gives me the same warning and thus I cannot run the code. Am I doing something wrong or is it so that one cannot use if/else or switch statements without flutter thinking there is dead code?

Actually you can use if/else and switch and any other statement inline in dart / flutter.

Use an immediate anonymous function

class StatmentExample extends StatelessWidget {
  Widget build(BuildContext context) {
    return Text((() {
      if(true){
        return "tis true";}

      return "anything but true";
    })());
  }
}

ie wrap your statements in a function

(() {
  // your code here
}())

I would heavily recommend against putting too much logic directly with your UI 'markup' but I found that type inference in Dart needs a little bit of work so it can be sometimes useful in scenarios like that.

Use the ternary operator

condition ? Text("True") : null,

Use If or For statements or spread operators in collections

children: [
  ...manyItems,
  oneItem,
  if(canIKickIt)
    ...kickTheCan
  for (item in items)
    Text(item)

Use a method

child: getWidget()

Widget getWidget() {
  if (x > 5) ...
  //more logic here and return a Widget

Redefine switch statement

As another alternative to the ternary operator, you could create a function version of the switch statement such as in the following post https://stackoverflow.com/a/57390589/1058292.

  child: case2(myInput,
  {
    1: Text("Its one"),
    2: Text("Its two"),
  }, Text("Default"));

I personally use if/else statement in children with this kind of block statement. It only supports on Dart version 2.3.0 above.

if / else

Column(
    children: [
        if (_selectedIndex == 0) ...[
          DayScreen(),
        ] else ...[
          StatsScreen(),
        ],
    ],
 ),

if / else if

Column(
    children: [
        if (_selectedIndex == 0) ...[
          DayScreen(),
        ] else if(_selectedIndex == 1)...[
          StatsScreen(),
        ],
    ],
 ),

multiple widgets example

Column(
    children: [
        if (_selectedIndex == 0) ...[
          DayScreen(),
          AboutScreen(),
          InfoScreen(),
        ] else if(_selectedIndex == 1)...[
          HomeScreen(),
          StatsScreen(),
        ],
    ],
 ),

In Dart, if/else and switch are statements not expressions. They don't return a value so you can't pass them to constructor params. If you have a lot of conditional logic in your build method, then it is a good practice to try and simplify it. For example, you can move self-contained logic to methods, and use if/else statements to initialize local variables which you can later use.

Using a method and if/else

Widget _buildChild() {
  if (condition) {
    return ...
  }
  return ...
}

Widget build(BuildContext context) {
  return new Container(child: _buildChild());
}

Using an if/else

Widget build(BuildContext context) {
  Widget child;
  if (condition) {
    child = ...
  } else {
    child = ...
  }
  return new Container(child: child);
}