Flutter Question posted in
The official Flutter documentation can be found here.

How to pass functions in Flutter

I really don’t understand how function passing works in Flutter.
When to use ()=> function(...); use this notation ?
I am trying to passing a function.This is my code:

        bottomSheetItem(context, 'İşlemi Sonlandır',
            () => _buildEvaluationBottomSheet(context)),

Widget bottomSheetItem(
    BuildContext context, String text, Function()? function) {
  return TextButton(
    onPressed: () {
      Navigator.pop(context);
      function;
    },
    child: Text(
      text,
      style: const TextStyle(fontSize: 12),
    ),
  );
}

_buildEvaluationBottomSheet(BuildContext context) {
  showModalBottomSheet(
    context: context,
    builder: (context) {
      return FractionallySizedBox(....);
    },
  );
}

Why this does not work ?
What are the optional function passing ways?

I tried to use function!; notation but I know that it doesnt work.
It must be function!();.
But why ?

Tags:

2

Answers


  1. 0

    In your case:

    Widget bottomSheetItem(
    BuildContext context, 
    String text, 
    void Function()? function,
) {
  ...
}

    you are trying to pass function(that could be null) without ANY params. but as function is nullable, you should use null checking and then call this function:

    ...
return TextButton(
        onPressed: () {
          Navigator.pop(context);
          function?.call();
        },
        child: Text(
          text,
          style: const TextStyle(fontSize: 12),
        ),
      );
...

    more info: dart functions

    Login or Signup to reply.
  2. 0

    There is nothing wrong with the way you passed _buildEvaluationBottomSheet function.

    The problem is the way you called it on text button pressed, when you put function; it will not be called, instead you should call it like this:

    function?.call();

    The "?" is because your function can be null, so it will be called only when it is not null.

    As I said there is nothing wrong with the way you passed the _buildEvaluationBottomSheet function but you can improve it by directly pass it without using the expression "() =>"

    Here is how your complete code will look like:

    bottomSheetItem(context, 'İşlemi Sonlandır', _buildEvaluationBottomSheet);
  Widget bottomSheetItem(
      BuildContext context, String text, Function(BuildContext context)? function) {
    return TextButton(
      onPressed: () {
        Navigator.pop(context);
        function?.call();
      },
      child: Text(
        text,
        style: const TextStyle(fontSize: 12),
      ),
    );
  }
  _buildEvaluationBottomSheet(BuildContext context) {
    showModalBottomSheet(
      context: context,
      builder: (context) {
        return Container();
      },
    );
  }
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search