How do I map a list of potentially null widgets?-CodePudding

I'm new to Flutter and haven't found much success in my brief online search for an answer to this, which is the reason for this post.

Here's the code in question:

// `myList` can potentially be null. 
children: widget.myList?.map((item) {
  return Text("Hi.");
}).toList(),

I'm trying to loop over a List<String>? of errors in my stateful widget, inside of the children: property of a Column.

Dart is telling me that I cannot map over a List<String>?, and suggests that I use myList?.map instead.

However, when I do that, the issue now becomes that children: expects a List<Widget> and can therefore not accept a List<Widget>? ...

I seem to be stuck in circuitous errors, but somehow I feel the solution is simple. I'm still learning about null-safety.

So tl;dr:

How do I reconcile between a potentially null list of widgets, and a property that expects a list of widgets that isn't null?

Solution

children: myList?.map((e) => Text(e)).toList() ?? [],

CodePudding user response：

If your List is List<Widget>?, you can add simply a null check like so:

children: _widgets?.map((item) => item).toList() ?? [Text('List was null')],

If your List is List<Widget?>? you can change it to:

children: _widgets?.map((item) => item ?? Text('widget was null')).toList() ?? [Text('List was null')],

If you want to map a List<String?> inside a Column

Column(
  children: _strings.map((e) => Text(e ?? 'String was null')).toList(),
)

Column(
  children: _strings.map((e) => e == null ? Text('was null') : Text(e)).toList(),
)

If your List is List<String>?

Column(
  children: _strings?.map((e) =>Text(e)).toList() ?? [Text('The list was null')],
)