Flutter

Question

我正在尝试更改 AppBar 的背景颜色，但它不起作用。

根据下图选择颜色0x673AB7时，AppBar 变成灰色而不是紫色。

import "package:flutter/material.dart";

void main() {
  runApp(new ControlleApp());
}

class ControlleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: "Controlle Financeiro",
      home: new HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        backgroundColor: new Color(0x673AB7),
      ),
    );
  }
}

Answer 1

看起来你的颜色是完全透明的。尝试将颜色更改为 0xFF673AB7

Answer 2

正如@Randal 提到的，您使用的是没有 alpha 值的十六进制代码。如果您没有指定它，它将是完全透明的。因此，您可以将前两个值用作 alpha，将其他六个值用作 RGB。

查看 Color class 源代码。有如下评论：

  /// 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).

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dart