Flutter (dart) ListView Builder Widget giving Invalid Arguments Error

Question

So, I have created a basic map

     var tracks = const [
    {
      'title':'Something',
      'subtitle':'Something'
    },
    {
      'title':'Something Else',
    },
    {
      'title':'Admission',
    },
    {
      'title':'University',
    },
    {
      'title':'Exam',
'subtitle':'Something'
    },
    {
      'title':'Job',
    },
  ];

And this is being called by a ListView.builder in the following manner:

var trackTitles = tracks[index];

and then being used like this:

return PrimaryMail(
              title: trackTitles['titles'],
            )

But, it is throwing an "Invalid Argument(s): titles error in the final build. No dart-analytics issues seen. The only error I see (info, not serious) is This class (or a class which this class inherits from) is marked as '@immutable', but one or more of its instance fields are not final: Home.tracks (must_be_immutable] lib\main.dart:18). [edit: the immutable issue has been fixed now by replacing var with final, but the original problem remains]

So, any way to understand why it is throwing an invalid argument even though the title key does exist?

The full code of this page is here.

Günter Zöchbauer · Accepted Answer · 2019-02-27 18:54:55Z

2

Add final before the field you declare in line lib\main.dart:18

If you have var there, replace var by final

answered Feb 27, 2019 at 18:54

Günter Zöchbauer

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6 Comments

Esh Over a year ago

Thank you. This solves the additional issue. But not the issue with Invalid Argument(s): titles. This error has now changed to

Another exception was thrown: 'package:flutter/src/widgets/text.dart': Failed assertion: line 237 pos 15: 'data != null': is not true.

Note that if I replace title: trackTitles['titles'], with title: 'Random String',, then it seems to work normally.

Günter Zöchbauer Over a year ago

Try title: trackTitles['titles']?.isNotEmpty ?? 'no tile'

Esh Over a year ago

Thank you. Just did. Now all of the tiles display "no tile". Which means that it is empty :( But do note that I have 6 sets/maps in tracks, and 6 tiles are being printed too (with the 'no tile' text).

Günter Zöchbauer Over a year ago

title: trackTitles['titles'], should be title: trackTitles['title'], (title instead of titles)

Günter Zöchbauer Over a year ago

I misinterpreted your code. I deleted my comment and posted a new one above.

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