CODEWITHSUNDEEP
flutterdart
Jessica
Jessica

Reputation: 9830

Call a function from a class gives me an error

I'm trying to run a function in another class. When I do that, I get an error message saying the following:

'_makeGetRequest' must have a method body because 'Home' isn't abstract. Try making 'Home' abstract, or adding a body to '_makeGetRequest'.dart(concrete_class_with_abstract_member)

Here's the code:

class Home extends StatelessWidget {
  _makeGetRequest(); // Error is here

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('CRUD Bro')),
      body: Center(
        child: Text('My App'),
      ),
    );
  }
}

_makeGetRequest() async {
    print('hello');
}

I tried making the Home class abstract, but the program doesn't work then. How can I call a function inside this class?

Upvotes: 2

Views: 10213

Answers (4)

Jalil Compaoré
Jalil Compaoré

Reputation: 404

You can't call methods directly inside the body of a class, at the same level as class members. You could call _makeGetRequest() in the build method, but that might not be what you want. When exactly do you want your method to run()?

Upvotes: 1

Jehad Nasser
Jehad Nasser

Reputation: 3565

According to your code, The method is in the same class not another, am I right?

Anyway, This error message is NOT saying "make it abstract to solve your problem", but in fact the compiler got confused, it reads this line:

_makeGetRequest();

then the compiler starts thinking like this: "hmmm this is a function's signature(function without body!), so this developer is trying to create an abstract class(because abstract class can have function without body) but this developer forgot to add abstract keyword like this abstract class Home... so, is it an abstract class and 'abstract' keyword is missing, or a normal class and function's body is missing?!!" so this lovely compiler will tell you its thoughts in an error message:

Try making 'Home' abstract, or adding a body to '_makeGetRequest'...

but both options are not solutions, it just got confused as I said.

But why this is the case?

because class is like the idea of 'Car', you can't drive the idea of car, but you need to create an object from that idea first, a BMW, then you can drive that BMW(in another word, you can call methods on objects not classes, because you can drive car's object but not the idea of Car).

To call methods you have at least these 4 options:

1- (In any language) to call methods from different class, create object first in that different class, then call them on that object: Do NOT use this with flutter's widgets, see option 4 below for that

class A {
  B b = B();
  b.makeGetRequest();
}

//..
class B {
  makeGetRequest() async { // NOT  PRIVATE(NO _)
    print('hello');
  }
}

2- (In any language) to call methods in same class, call it in the constructor, like Doc's answer.

3- (In Flutter) to call methods in same class, call it in the Build, like Doc's answer also.

4- (In Flutter) to call methods in different class, you need a bloc, see my answer here for more details.

Upvotes: 4

Doc
Doc

Reputation: 11671

class Home extends StatelessWidget {
  Home(){
    _makeGetRequest(); // option 1. to call the function only when the class is instantiated
  }
  @override
  Widget build(BuildContext context) {
    _makeGetRequest(); // option 2. to call the function on every rebuild
    return Scaffold(
      appBar: AppBar(title: Text('CRUD Bro')),
      body: Center(
        child: Text('My App'),
      ),
    );
  }
}

_makeGetRequest() async {
    print('hello');
}

Use either option 1 or 2.

Upvotes: 4

Edward Garson
Edward Garson

Reputation: 2186

The problem you're having is that you're making a method call within a class declaration. When should _makeGetRequest be called? You can call that method from within the body of the build() method you wrote (or any other method you add to the class for that matter). Does that make sense? Perhaps you could explain further what you want to achieve, there might be a better way still.... Cheers

Upvotes: 0

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