How to conditionally add widgets to a list?

Question

In flutter, widgets such as Row/ListView/Stack don't handle null children. So if we want to conditionally add widgets as children I usually do the following:

Row(   children: <Widget>[     foo == 42 ? Text("foo") : Container(),   ], ); 

But this feels weird to add an empty container.

Another solution is a where filter :

Row(   children: <Widget>[     foo == 42 ? Text("foo") : null,   ].where((t) => t != null).toList(), ); 

This solves the empty container problem but we still have an ugly ternary and it is tiresome to write.

Is there any better solution?

Answer 1

EDIT:

Since Dart 2.2, new syntaxes supports this natively:

Column(   children: [     if (foo != null) Text(foo),     Bar(),   ], ); 

---

This problem is currently debated on github here.

But for now, you can use dart sync* functions:

Row(   children: toList(() sync* {     if (foo == 42) {       yield Text("foo");     }   }), ); 

where toList is:

typedef Iterable<T> IterableCallback<T>();  List<T> toList<T>(IterableCallback<T> cb) {   return List.unmodifiable(cb()); } 

---

Not only it solves the conditional addition problem; it also allows for a "spread operator" thanks to yield*. Example:

List<Widget> foo;  Row(   children: toList(() sync* {     yield Text("Hello World");     yield* foo;   }), ); 

Answer 2

The new Dart syntax allows 'if' in lists, which leads to this simple solution:

Row(   children: <Widget>[     if (foo == 42) Text("foo"),   ], );