Use variable in Text Widget

Question

I'm trying to use a variable in Text Widget, it says Invalid const value, so, I need to use a const, but I'm using Text Widget in a dynamic way. Is there a way to use a Text with variables? or is there another Widget that I could use?

I have something like this:

class PlaceCardState extends StatelessWidget {
  PlaceCardState(this._placeCard);
  Place _placeCard;

  @override
  Widget build(BuildContext context) {
    return ListTile(
            leading: const Icon(Icons.album),
            title: Text(_placeCard.title),
            subtitle: const Text('Come and dance tonight!'),
          );
  }
}

place.dart

class Place {
  Place([this.title = '', this.description = '', this.image='',     this.value=0.0]);
  String title;
  String description;
  String image;
  double value;
}

I get this issue:

What do you mean "variable"? As in a variable widget or the text needs to change? — Phix
– Phix, Commented Aug 10, 2018 at 18:32
I need to use a variable, like var myText = 'My Text'; and print that into the Text(myText) but it asks me to use a const, but, in my code, I need to use a class property _placeCard.title, that's a variable, not a const makes sense? — Joseph Arriaza
– Joseph Arriaza, Commented Aug 10, 2018 at 18:34
In that way I should use something like: title: Text('I am ${_placeCard.title}'), but I got the same — Joseph Arriaza
– Joseph Arriaza, Commented Aug 10, 2018 at 18:42

Peter Haddad · Accepted Answer · 2018-08-10 18:36:44Z

5

Change this:

const ListTile(
        leading: const Icon(Icons.album),
        title: Text(_placeCard.title),
        subtitle: const Text('Come and dance tonight!'),
      );

into this:

const ListTile(
        leading: const Icon(Icons.album),
        title: const Text(_placeCard.title),
        subtitle: const Text('Come and dance tonight!'),
      );

Since in your screenshot ListTile is a constant then all the properties need to be constant also, therefore add const before Text(_placeCard.title),

answered Aug 10, 2018 at 18:36

Peter Haddad

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1 Comment

Jonah Williams Over a year ago

This will only work if _placeCard.title is constant as well

JSAN L. · Accepted Answer · 2018-08-11 22:00:18Z

Const will be assumed for Icon and Text, as they have to be constant, so that the ListTile can be constant as a whole.

So it's the same to write:

const ListTile(
    leading: const Icon(Icons.album),
    title: const Text(_placeCard.title),
    subtitle: const Text('Come and dance tonight!'),
  );

as

const ListTile(
    leading: Icon(Icons.album),
    title: Text(_placeCard.title),
    subtitle: Text('Come and dance tonight!'),
  );

But you seem to confuse the meaning of const anyway, as this probably won't work in your application.

From news.dartlang.org,

"const" has a meaning that's a bit more complex and subtle in Dart. const modifies values. You can use it when creating collections, like const [1, 2, 3], and when constructing objects (instead of new) like const Point(2, 3). Here, const means that the object's entire deep state can be determined entirely at compile time and that the object will be frozen and completely immutable

so that means that you could say

const ListTile(
    leading: Icon(Icons.album),
    title: Text("foo"),
    subtitle: Text('Come and dance tonight!'),
  );

but not create that Object constant while running the application, as you don't have all data at compile-time.

You should just not use const and then it should be alrighto.

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