Dart null safety complains about a function becoming null despite the null check being there

Question

So I have a following class which takes onPressed as a prop which can be null:

class Class1 {
  final Function? onPressed;
  
  const Class1({ this.onPressed });
  
  callMethod() {
    if(onPressed != null) {
      onPressed(); // Complains here
    }
  }
}

As you can see I have a check if onPressed is null. But dart still complains with this message The function can't be unconditionally invoked because it can be 'null'. (view docs) Try adding a null check ('!'). Please help me.

Note that in your case, you could just remove the `if` statement and use `onPressed?.call();`. — jamesdlin, Mar 07 '21 at 08:46

score 10 · Accepted Answer · answered Mar 07 '21 at 08:39

10

Try adding a null check ('!') as compiler suggests

class Class1 {
  final Function? onPressed;

  const Class1({this.onPressed});

  callMethod() {
    if (onPressed != null) {
      onPressed!(); //Note: ! is added here
    }
  }
}

answered Mar 07 '21 at 08:39

Pavel Shastov

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if we do this, when press wouldnt it throws "Null check operator used on a null value "? – vontdeux Sep 29 '21 at 07:47
2

In this case we have a check at runtime "if (onPressed != null)", so it is not possible to get "Null check" exception here – Pavel Shastov Sep 29 '21 at 19:34

Dart null safety complains about a function becoming null despite the null check being there

1 Answers1