[C#] Enum - FlagsAttribute - Remove

在官方文章 - How to: Customize the Appearance of Rows in the Windows Forms DataGridView Control 內看到這段語法

e.PaintParts &= ~DataGridViewPaintParts.Focus;

個人筆記內有紀錄過 Enum Attribute 兩種移除方式

// 寫法一
var result = EnumSource ^ FlagRemove;

// 寫法二
var result = EnumSource & ~FlagRemove;

本篇筆記重點在於了解 EnumSource & ~FlagRemove; 和 EnumSource &= ~FlagRemove; 兩者差異

• EnumSource & ~FlagRemove：不會移除 EnumSource 內的 FlagRemoveEnum，但回傳值是移除的
• EnumSource &= ~FlagRemove：直接移除 EnumSource 內的 FlagRemoveEnum

寫個簡易範例來驗證

using System;

namespace EnumFlags
{
    class Program
    {
        static void Main(string[] args)
        {

            Days source = Days.Tuesday | Days.Thursday | Days.Saturday;
            Days flagRemove = Days.Thursday;
            Console.WriteLine($"初始值：{source}");

            // 使用 source & ~flagRemove 不會改變 source
            Days result = source & ~flagRemove;
            Console.WriteLine($"source & ~flagRemove result 值：{result} "); // Output: Tuesday、Saturday
            Console.WriteLine($"source & ~flagRemove source 值：{source} "); // Output: Tuesday、Thursday、Saturday

            // 使用 source &= ~flagToRemove 直接改變 source
            source &= ~flagRemove;
            Console.WriteLine($"source &= ~flagToRemove source 值：{source}"); // Output: Tuesday、Saturday
        }
    }

    // 沒有特別宣告的話，Enum 預設是 int
    [Flags]
    public enum Days
    {
        Monday = 1,
        Tuesday = 2,
        Wednesday = 4,
        Thursday = 8,
        Friday = 16,
        Saturday = 32,
        Sunday = 64,

        All = Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday
    };
}

• 延伸閱讀
• [C#] Enum - FlagsAttribute
• 參考資料
• [C#.NET] 二進制運算 Enum of Flags