c# - ContentAlignment 枚举值的解释

Question

System.Drawing.ContentAlignment 枚举如下所示:

namespace System.Drawing
{
    // Summary:
    //     Specifies alignment of content on the drawing surface.
    [Editor("System.Drawing.Design.ContentAlignmentEditor, System.Drawing.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(UITypeEditor))]
    public enum ContentAlignment
    {
        TopLeft = 1,
        TopCenter = 2,
        TopRight = 4,
        MiddleLeft = 16,
        MiddleCenter = 32,
        MiddleRight = 64,
        BottomLeft = 256,
        BottomCenter = 512,
        BottomRight = 1024,
    }
}

为什么以某种标志样式定义值？为什么缺少 8 和 128？

Answer 1

也许让 ContentAlignment 枚举参与按位运算。

But why it isn't decorated with FlagsAttribute?

因为它不打算被客户端用作按位标志，所以他们没有用 FlagsAttribute 修饰枚举。

您可以引用 .net framework 源代码以了解它们如何很好地使用 ContentAlignment 进行按位运算。

ControlPaint.TranslateAlignment使用它，您可以在 top of the class 中看到带有按位或的声明

private static readonly ContentAlignment anyRight  = ContentAlignment.TopRight | ContentAlignment.MiddleRight | ContentAlignment.BottomRight;
private static readonly ContentAlignment anyBottom = ContentAlignment.BottomLeft | ContentAlignment.BottomCenter | ContentAlignment.BottomRight;
private static readonly ContentAlignment anyCenter = ContentAlignment.TopCenter | ContentAlignment.MiddleCenter | ContentAlignment.BottomCenter;
private static readonly ContentAlignment anyMiddle = ContentAlignment.MiddleLeft | ContentAlignment.MiddleCenter | ContentAlignment.MiddleRight;

这应该回答“为什么以某种标志样式定义值”。

Why are 8 and 128 missing?

我对此一无所知。如果有人有，将不胜感激。