flutter: NoSuchMethodError:the method ‘-‘ was called on null

写了个Tween<Color> 报错： NoSuchMethodError:the method '-' was called on null

color = Tween<Color>(begin: Colors.green, end: Colors.red).animate( CurvedAnimation( parent: controller, curve: Interval(.0, .6, curve: Curves.ease)));

写错了， 正确写法是使用ColorTween：

color = ColorTween(begin: Colors.green, end: Colors.red).animate( CurvedAnimation( parent: controller, curve: Interval(.0, .6, curve: Curves.ease)));

class Tween 应该处理的是double类型渐变效果， 颜色渐变应使用ColorTween

class ColorTween extends Tween<Color?> { /// Creates a [Color] tween. /// /// The [begin] and [end] properties may be null; the null value /// is treated as transparent. /// /// We recommend that you do not pass [Colors.transparent] as [begin] /// or [end] if you want the effect of fading in or out of transparent. /// Instead prefer null. [Colors.transparent] refers to black transparent and /// thus will fade out of or into black which is likely unwanted. ColorTween({ Color? begin, Color? end }) : super(begin: begin, end: end); /// Returns the value this variable has at the given animation clock value. @override Color? lerp(double t) => Color.lerp(begin, end, t); }

网上找到类似问题： flutter报错：NoSuchMethodError: The method '>' was called on null.

是由于 Column或者Row的children里有Flexible导致。

 

不得不说，对Flutter Tween类还是不熟悉，而且Flutter类型判断还是不完善。