飞镖设置参数的默认值 [英] Dart set default value for parameter
本文介绍了飞镖设置参数的默认值的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
在 Flutter
框架中,我试图将参数的默认值设置为 borderRadius
,在此示例中如何我实现了吗?我得到可选参数的默认值必须为常量
尝试设置该值时会出错,例如:
in Flutter
framework i'm trying to set default value for parameters as borderRadius
, in this sample how can i implementing that? i get Default values of an optional parameter must be constant
error when i try to set that, for example:
class SimpleRoundButton extends StatelessWidget {
final BorderRadius borderRadius;
SimpleRoundButton({
}):this.borderRadius = BorderRadius.circular(30.0);
}
class SimpleRoundButton extends StatelessWidget {
final BorderRadius borderRadius= BorderRadius.circular(30.0);
SimpleRoundButton({
this.borderRadius,
});
}
class SimpleRoundButton extends StatelessWidget {
final BorderRadius borderRadius;
SimpleRoundButton({
this.borderRadius= BorderRadius.circular(30.0)
});
}
所有这些样本都不正确
推荐答案
BorderRadius.circular()
不是const函数,因此您不能将其用作默认值。
BorderRadius.circular()
is not a const function so you cannot use it as a default value.
要设置const圆形边框,您可以使用 BorderRadius.all
函数,如下所示:
To be able to set the const circular border you can use BorderRadius.all
function which is const like below:
class SimpleRoundButton extends StatelessWidget {
final BorderRadius borderRadius;
SimpleRoundButton({
this.borderRadius: const BorderRadius.all(Radius.circular(30.0))
});
@override
Widget build(BuildContext context) {
return null;
}
}
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