CODEWITHSUNDEEP
flutterdart
Pamela
Pamela

Reputation: 475

Dart - An expression whose value can be null must be null-checked before it can be dereferenced

This was my Dart code after initializing fun by adding ?

However, it is still not working and throws an error that says "An expression whose value can be null must be null-checked before it can be dereferenced"

int add(int a, int b) => a + b;

Function? fun;

void main() {
  fun = add;
  
  var result = fun(20, 30);
  
  print("Result is ${result}");
}

How do I null-check fun?

Upvotes: 1

Views: 1292

Answers (1)

Lesiak
Lesiak

Reputation: 25936

You compare against a null, the analyzer deduces that after the successfull check the variable is not null:

void testFunction(Function? f) {
  if (f != null) {
     var result = f(20, 30);
     print("Result is ${result}");
  }
}

One caveat is it does not currently work with global variables:

The analyzer can’t model the flow of your whole application, so it can’t predict the values of global variables or class fields.

See https://dart.dev/null-safety#using-variables-and-expressions

Also note that there isn’t a null-aware function call operator, but you can write:

function?.call(arg1, arg2);

Upvotes: 1

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