CODEWITHSUNDEEP
flutterdart
lucky
lucky

Reputation: 315

flutter : how to fix The method '[]' can't be unconditionally invoked because the receiver can be 'null'

I'm trying to fix errors on my project after migration to null safety . i have error on this line :

 opacity: animation["opacity"],
        child: Transform.translate(
            offset: Offset(0, animation["translateY"]  ), child: child),

error : The method '[]' can't be unconditionally invoked because the receiver can be 'null'

My code :

class FadeAnimation extends StatelessWidget {
  final double delay;
  final Widget child;

  FadeAnimation(this.delay,   this.child);

  @override
  Widget build(BuildContext context) {
    final tween = MultiTrackTween([
      Track("opacity")
          .add(Duration(milliseconds: 500), Tween(begin: 0.0, end: 1.0)),
      Track("translateY").add(
          Duration(milliseconds: 500), Tween(begin: -130.0, end: 0.0),
          curve: Curves.easeOut)
    ]);

    return ControlledAnimation(
      delay: Duration(milliseconds: (500 * delay).round()),
      duration: tween.duration,
      tween: tween,
      child: child,
      builderWithChild: (context, child, animation) => Opacity(
        opacity: animation["opacity"],
        child: Transform.translate(
            offset: Offset(0, animation["translateY"]  ), child: child),
      ),
    );
  }
}

How I can fix it ?

Thanks in advance

Upvotes: 0

Views: 726

Answers (2)

Valentin Vignal
Valentin Vignal

Reputation: 8288

It means your object animation might be null (I guess its type is Map?). So you cannot do animation['yourKey'] directly as null['yourKey'] is not valid.

You have several solutions:

  1. Try to change the type of animation to Map if possible.
  2. If animation has to be Map? but you are sure it won't be null when you use it, you can do
animation!['yourKey']
  1. If it can be null then you can do:
animation?['yourKey'], // If it is okay to use a `null` value here
animation?['yourKey'] ?? defaultValue, // If you need to use a non-null value

For example, for you opacity you can to:

opacity: animation?["opacity"] ?? 0,

Upvotes: 2

Arbiter Chil
Arbiter Chil

Reputation: 1285

if your using nullsafety

final double? delay;
final Widget? child;

then for calling them will be end at !

e.g delay! or child!

Upvotes: 0

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