CODEWITHSUNDEEP
flutterequality
kopemik685
kopemik685

Reputation: 3

Why is my list equal check not working when they look the same in Flutter?

Part of my Flutter program creates a list and later checks to see if the list is equal to another. However, when I test this, it returns false. I've done a series of printout statements to check why they aren't equal and they look the same, but it keeps returning false.

The code:

print("programList: " + programList.toString());
//print(programList.runtimeType);
var testResult = (programList == ["apple", "apple", "banana"]);
print("programList are correct: " + testResult.toString());
for(var i in programList){
  print(i + ": " + i.runtimeType);
}
if(programList == ["apple", "apple", "banana"]){
  print("in test loop");
  //do stuff
}

This is the print out:

I/flutter ( 1429): programList: \[apple, apple, banana\]
I/flutter ( 1429): programList are correct: false

Exception caught by gesture
The following \_TypeError was thrown while handling a gesture:
type '\_Type' is not a subtype of type 'String' of 'other'

The error didn't start showing up until the runtimeType for loop, but before that, it didn't print "in test loop".

I tried adding all of those print statements to see what was happening. I tried adding runtimeTypes to try to understand if they were coming up with different types, but that caused an error of it's own.

Upvotes: 0

Views: 271

Answers (1)

powerman23rus
powerman23rus

Reputation: 1583

Because dart's default is to compare the objects by reference. As the result, you have different references for 2 arrays with the same values.

To make it work you have to use DeepCollectionEquality

import 'package:collection/collection.dart';

void main() {
  Function equality = const DeepCollectionEquality().equals;
  final programList = ["apple", "apple", "banana"];
  print(equality(programList, ["apple", "apple", "banana"]));
}

Upvotes: 1

Related Questions