问题描述
例如，当您使用Colors.blue时，它将返回一个恒定的Color对象，但是如果您选择使用阴影(即Colors.blue [300])，则该对象不是恒定的.例如，当您具有采用可选Color参数的方法时，该方法的默认值必须为常数，这一点很重要.那么我们如何使颜色阴影保持不变?
When you use Colors.blue, for example this returns a constant Color object, but if you choose to use a shade instead, i.e. Colors.blue[300], then this object is NOT constant. This is important, for example, when you have a method that takes an optional Color parameter, whose default value must be constant. So how do we make a Color shade constant?
static const Color mainColor = Colors.blue \\All good!
static const Color shade = Colors.blue[400] \\ERROR: Const variables must be initialized with a constant value
推荐答案
不能.若要选择特定的阴影，应使用[]运算符，就像调用方法一样，并且由于方法返回的值在运行时会有所不同，因此从方法调用返回的值不能用作常量. /p>
You can't. To choose a specific shade, you should use the [] operator, which is just like calling a method, and since the value a method returns varies on run-time, the value returned from a method call cannot be use as constant.
如果您的情况如此简单，只需使用Colors.blue[400]的实际值，即Color(0xFF42A5F5).
If your situation is as simple as this one, just use the real value of Colors.blue[400], which is Color(0xFF42A5F5).
这篇关于色调不是Flutter中的恒定值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！