How to safely call (with null check) a variable of type Function

Question

Is there an easy way to invoke the function with null check ?

Function(String) onTextReady;

Is there an easy way to safely invoke this function. In Kotlin for example I would use invoke:

onTextReady?.invoke('Hello world');

I tried onTextReady?.('Hello world'); but Dart doesn't support this.

Answer 1

Well, short answer, no (with the operator). The null-aware ?. operator in Dart will work only with object call to members, not to null-check a function execution directly.

In this case bellow, it would work:

class MyClass {
  Function(String s) onTextReady = (s) => print(s);
}

main() {
  var nullObject;
  nullObject?.onTextReady('null'); // do nothing

  var notNull = MyClass();
  notNull?.onTextReady('not null'); // print 'not null'
}

You would need to check it manually (!= null) to be null-safe:

main() {
  Function(String) onTextReady;

  if(onTextReady != null) {
    onTextReady('null');
  }

  Function(String) onTextReady2 = (s) => print(s);

  if(onTextReady2 != null) {
    onTextReady2('not null');
  }
}