CallBack Function with null safety

Question

I have a widget like this

class googleMapComponent extends StatefulWidget {
   Function(LatLng pos) OnPositionChangeCallback;

googleMapComponent({
this.OnPositionChangeCallback,})

using nullsafety i get this error

The parameter 'OnPositionChangeCallback' can't have a value of 'null' because of its type, but the implicit default value is 'null'.

I know using required will fix it but I don't want it to be required

Solution

If this function is required just make the parameter required and the language will enforce you to always pass a function to the constructor of googleMapComponent

class googleMapComponent extends StatefulWidget {
   Function(LatLng pos) OnPositionChangeCallback;

googleMapComponent({required this.OnPositionChangeCallback,})

Otherwise make the function nullable with the ? keyword.

this is the final Answer to this question

final Function(LatLng pos)? OnPositionChangeCallback;

Comments

[Darshan]

You can use Function(LatLang? pos) to allow null values or use the ! operator when passing values.

[Ardeshir ojan]

@DarShan the first solution doesn't work and for the second one i don't want to send value because there is a lot of CallBack functions for this widget

[Ardeshir ojan]

no, it is not required and for the second solution you mean like this Function(LatLang? pos) if yes no it doesn't work either

[croxx5f]

The whole function should be marked as nullable ` Function(String pos) OnPositionChangeCallback` ,not just its parameter. Just remember to always check if its not null before usage. Was that what you were looking for @Ardeshirojan?

[Ardeshir ojan]

yes, this is correct thank you.i will update your answer with the final answer