Run method only if exists

Asked Sep 06 '20 at 22:48

Active Sep 06 '20 at 23:08

Viewed 28 times

How can I run a method only if it exists? I tried the following but it didn't work:

widget.onChangeHandler ?? widget.onChangeHandler(selectedItem);

Here's the full code:

class MyWidget extends StatefulWidget {
  final Function onChangeHandler;
  MyWidget({this.onChangeHandler});

  @override
  MyWidgetState createState() => MyWidgetState();
}

class MyWidgetState extends State<MyWidget> {
  void onTap(dynamic selectedItem) {
    widget.onChangeHandler(selectedItem); // Here's where I call the method
  }
  // ...

edited Sep 06 '20 at 23:08

asked Sep 06 '20 at 22:48

Jessica

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What do you mean `only if it exists` ? – void Sep 06 '20 at 22:50
@void The parent widget has a parameter `onChangeHandler` which is not required. What I want to do, is run `onChangeHandler` only if a function was passed into the argument. – Jessica Sep 06 '20 at 22:51
Can you provide a minimal reproducible code ? @Jessica – void Sep 06 '20 at 23:03
`widget.onChangeHandler?.call(selectedItem)` – jamesdlin Sep 06 '20 at 23:08
@jamesdlin Nice! Can you explain the `call`? – Jessica Sep 06 '20 at 23:09

Run method only if exists

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