颤振使用哪种颜色系统，为什么我们使用“ const Color”而不是“ new Color” [英] What color system does flutter use and why do we use `const Color` instead of `new Color`

问题描述

今天我走过下面的代码片段，这些代码实现了抖动中的梯度

Today I came over following snippet of code that implements gradient in flutter

return new Container(
  ...
  decoration: new BoxDecoration(
    gradient: new LinearGradient(
      colors: [
        const Color(0xFF3366FF), 
        const Color(0xFF00CCFF),
      ]
      begin: const FractionalOffset(0.0, 0.0),
      end: const FractionalOffset(1.0, 0.0),
      stops: [0.0, 1.0],
      tileMode: TileMode.clamp
    ),
  ),
),

2个问题：

1） 0xFF3366FF 是什么颜色系统？

1) What color system is 0xFF3366FF this? it looks somewhat similar to HEX, but it isn't.

2）为什么我们将 const 用作 const Color（）反对 new Color（）我理解两者之间的不同，但是这里的const对我来说并不直观希望它会创建一个 new Color（）类实例，类似于我们使用 new Text（ Some text）。如果需要使用const，为什么 TileMode.clamp 也不是const？

2) Why do we use const for const Color() opposed to new Color() I understand different between both, but const here feels unintuitive for me, I'd expect it to be creating a new Color() class instance, similarly to how we use new Text("Some text"). If it needs to be const, why isn't TileMode.clamp also a const?

推荐答案

从Flutter来源

class Color {
  /// Construct a color from the lower 32 bits of an [int].
  ///
  /// The bits are interpreted as follows:
  ///
  /// * Bits 24-31 are the alpha value.
  /// * Bits 16-23 are the red value.
  /// * Bits 8-15 are the green value.
  /// * Bits 0-7 are the blue value.
  ///
  /// In other words, if AA is the alpha value in hex, RR the red value in hex,
  /// GG the green value in hex, and BB the blue value in hex, a color can be
  /// expressed as `const Color(0xAARRGGBB)`.
  ///
  /// For example, to get a fully opaque orange, you would use `const
  /// Color(0xFFFF9000)` (`FF` for the alpha, `FF` for the red, `90` for the
  /// green, and `00` for the blue).
  const Color(int value) : value = value & 0xFFFFFFFF;

const 实例已规范化。

如果您的代码中有多个 const Color（0xFF00CCFF），则只会创建一个实例。

If you have multiple const Color(0xFF00CCFF) in your code, only one instance will be created.

const 实例在编译时进行评估。
这是在Dart VM中加载代码的时间，但是在Flutter生产中，使用了AoT编译，因此const值提供了较小的性能优势。

const instances are evaluated at compile time. In the Dart VM this is when the code is loaded, but in Flutter production AoT compilation is used and const values therefore provide a small performance benefit.

请参见还 const构造函数实际上如何工作？

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