CODEWITHSUNDEEP
constructordartflutterinitializationwidget
Joel Broström
Joel Broström

Reputation: 4060

Use constructor arguments to evaluate final values depending on each other. Flutter / Dart

I have a widget that takes a number representing pages allowed to be displayed on the screen. If the device is weak a bool can be passed that overrides the initial value. However, since all values are final I must evaluate it in the constructor before the value is set.

class _A extends StatefullWidget{

  _A(this.limitPages, 
    this.pagesToDisplay: limitPages ? 10 : pagesToDisplay,
  )

  final int pagesToDisplay;
  final bool limitPages;
}

I could declare it in the initializer list, but then I can't pass an argument for pagesToDisplay.

class _A extends StatefullWidget{
  _A(this.limitPages)
    :this.pagesToDisplay: limitPages ? 10 : pagesToDisplay

  final int pagesToDisplay;
  final bool limitPages;
}

Is there any way to assert a statement in/before the constructor sets the final value?

Upvotes: 3

Views: 3884

Answers (1)

Günter Zöchbauer
Günter Zöchbauer

Reputation: 657416

If you want to use a parameter in the initializer list, the parameter can't be an initializing parameter, and you need to do the initializing in the initializer list instead:

class _A {
  _A(bool limitPages, int pagesToDisplay)
      : limitPages = limitPages,
        pagesToDisplay = limitPages ? 10 : pagesToDisplay;

  final int pagesToDisplay;
  final bool limitPages;
}

Upvotes: 9

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