Reputation: 31391

Flutter check if variable is NaN

I have var number; and it gets assigned by some calculations.

If I do print(number); I get NaN as response;

I expected that I would be able to do something like

if (number is NaN)

But I get NaN is not defined. How to check if variable is NaN in flutter?

Upvotes: 24

Answers (6)

goldenEd

Reputation: 13

Use isFinite property https://api.flutter.dev/flutter/dart-core/num/isFinite.html

value.isFinite

Upvotes: 0

felix-ht

Reputation: 2075

You cannot check for nan by comparing it to the double.nan constant. isNan is the way to go.

yourNumber.isNaN

Why does comparing to double.nan not work?

print(double.nan == double.nan);
// prints false
print(double.nan.isNaN);
// prints true

This is because by definition NaN is not equal to itself. In fact if you would want to implement a NaN check yourself you would do it like so:

bool isNan(double x) => x != x;

This also has the consequence that if you save a NaN into any other kind of object, the object will no longer be equal to itself (as long as the NaN is used in the comparison - like with data classes). This can lead to unexpected behavior. You could use this code to check for this case.

bool hasNan(Object? x) => x != x;

In general this is true for all languages i am aware of - not just dart - as it's a hardware thing.

Upvotes: 15

Abdullah Razzaq

Reputation: 119

Use (number.isNaN) condition instead

Upvotes: -1

Jacob Phillips

Reputation: 9274

num types have an isNaN property, or you can see if the var is equal to double.nan. You should define the variable using num instead of var.

https://api.dartlang.org/stable/1.24.3/dart-core/num-class.html

Upvotes: 0