What is the best way to fix this simple Dart Null error?-CodePudding

I'm following along with an online course and the instructor gave this example of code...but it now throws a Null Safety error...

"The parameter 'namePerson' can't have a value of null beccause of its type..but the implicit default value is null'

void main() {     
     
  greet(greeting: 'Hey', namePerson: 'Cindy');
  }

void greet({String namePerson, String greeting}){
    print("$greeting $namePerson");
  }

Now after researching this I found I could fix the error in three ways..by placing a ? after the word String...or by placing the word 'required' before the String...or by giving a default value...eg.

void greet({String namePerson = 'Bob', String greeting = 'Sam'}){

I don't really understand though what we should ideally do in a situation like this? I watched a Youtube video on null safety errors'..but it is still a bit beyond my current comprehension level. Can someone explain how and why you would solve this error? Thanks for any help or tips!

CodePudding user response：

You should start by asking you "In the context of my function, are my parameters required of optionnal" ?

Clearly, a function to greet someone should have :

a required, so non nullable namePerson: you must have a name to greet someone. And you cannot have a defaultValue (arbitrary "Bob" ? why ? it doesn't really make sense)
an optional greeting but with a default value, so non nullable also : you must say something to him to greet him

So I'd have it like :

void greet({required String namePerson, String greeting = 'Hello'}){

So basically, you should separate the 2 aspects :

should the inner body of my function works with a nullable or non nullable value ?
should my function take a required, optional but non nullable (so with default) value, or a totally optional one (!nullable) ?

Hope that helped

CodePudding user response：

Use null check operator . Your code will run. Use the code like below. Thanks.

void main() {     
         
      greet(greeting: 'Hey', namePerson: 'Cindy');
      }
    
    void greet({String? namePerson, String? greeting}){
        print("$greeting! $namePerson!");
      }