[英]C# flag enum toggle by value or name
我有一個 Flags enum
,想通過它的 ( long
) 值來切換一些值。
[Flags]
public enum Permissions : long
{
Value0 = 0,
Value1 = 0x1,
Value2 = 0x2,
Value3 = 0x4,
//etc
}
我使用long
字段通過EF
將實際權限存儲在數據庫中,例如:
public Permissions UsersPermissions { get; set; }
從客戶端,我一一獲取值以通過enum
切換正確的值,因此如果數據庫字段包含
`Value1 | Value2 | Value3`
我得到 4 我必須從用戶的權限中刪除 Value3。
enum
值? 我已經嘗試過usersPermissions |= permissionValue
但它說我不能在long
和Permission
Types 上使用|=
運算符。
您必須在適當的點對long
和Permissions
進行一些轉換,如下所示:
Permissions perms = Permissions.Value1 | Permissions.Value2 | Permissions.Value3;
Console.WriteLine(perms); // Value1, Value2, Value3
long toRemove = 4;
// OR: long toRemove = (long) Permissions.Value3;
perms = (Permissions) ((long)perms & ~toRemove); // Use "& ~X" to remove bits set in X.
Console.WriteLine(perms); // Value1, Value2
這里重要的是~toRemove
返回~toRemove
的按位補toRemove
,從而為您提供一組位標志,您可以使用原始值&
以關閉在toRemove
中設置的所有位。
你必須投perms
到long
,以做到這一點&
操作。
最后,通過&
獲得所需的結果后,您必須將long
回Permissions
以獲得正確的枚舉類型作為最終答案。
據我所知,您的輸入是一個數字,您希望它是一個Permissions
。 好吧,即使它不是離散值之一,您也可以直接轉換它。 如果它是標志值之一的組合,那甚至可以“弄清楚”。 C# 枚舉以這種方式進行強制轉換非常聰明。
這是一個代碼示例,可以執行您想要的操作
[Flags]
public enum TestEnum : long
{
ValueNone = 0, // You can't really "have" a Value0, it's an absence of values
Value1 = 0x1,
Value2 = 0x2,
Value3 = 0x4,
Value4 = 0x8
}
foreach(var enumVal in Enum.GetValues(typeof(TestEnum)))
{
Console.WriteLine("val is: {0} long is: {1}", enumVal, (long)enumVal);
}
{
Console.WriteLine("Start with 1 and 3, remove 3 from number");
var testEnum = TestEnum.Value1 | TestEnum.Value3;
Console.WriteLine("testEnum is: {0}({1})", testEnum, (long)testEnum);
long testVal = 4; // TestEnum.Value3
var removeEnum = (TestEnum)testVal;
removeEnum = ~removeEnum;
testEnum &= removeEnum;
Console.WriteLine("testEnum is: {0}({1})", testEnum, (long)testEnum);
}
{
Console.WriteLine("Start with 1, 2, 4 and remove 1 and 4 from number");
var testEnum = TestEnum.Value1 | TestEnum.Value2 | TestEnum.Value4;
Console.WriteLine("testEnum is: {0}({1})", testEnum, (long)testEnum);
long testVal = (long)TestEnum.Value1 | (long)TestEnum.Value4; // Could also have added them
var removeEnum = (TestEnum)testVal;
Console.WriteLine("Removing: {0}({1})", removeEnum, (long)removeEnum);
testEnum &= ~removeEnum;
Console.WriteLine("testEnum is: {0}({1})", testEnum, (long)testEnum);
}
這是通過最后一個元素的值獲得枚舉限制的方法:
{
// Check the value to see what the range of the enumeration is
var lastVal = Enum.GetValues(typeof(TestEnum)).Cast<TestEnum>().Last();
long limit = (long)lastVal * 2;
Console.WriteLine("Limit of flags for TestEnum is: " + limit);
Func<long, bool> testLambda = x => x < limit;
Console.WriteLine("Value of {0} within limit: {1}", 14, testLambda(14));
Console.WriteLine("Value of {0} within limit: {1}", 16, testLambda(16));
Console.WriteLine("Value of {0} within limit: {1}", 200, testLambda(200));
Console.WriteLine("Value of {0} within limit: {1}", 0, testLambda(0));
Console.WriteLine("Out of range looks like: " + (TestEnum)17);
Console.WriteLine("In range looks like: " + (TestEnum)14);
}
輸出:
val is: ValueNone long is: 0
val is: Value1 long is: 1
val is: Value2 long is: 2
val is: Value3 long is: 4
val is: Value4 long is: 8
Start with 1 and 3, remove 3 from number
testEnum is: Value1, Value3(5)
testEnum is: Value1(1)
Start with 1, 2, 4 and remove 1 and 4 from number
testEnum is: Value1, Value2, Value4(11)
Removing: Value1, Value4(9)
testEnum is: Value2(2)
Limit of flags for TestEnum is: 16
Value of 14 within limit: True
Value of 16 within limit: False
Value of 200 within limit: False
Value of 0 within limit: True
Out of range looks like: 17
In range looks like: Value2, Value3, Value4
我完全承認上面可能有更好的方法,但從根本上說,如果您有一個[Flags]
枚舉,因此其中的所有內容在一定程度上都是“有效的”(所有組合都可以),只需檢查是否您的值超出范圍,然后將其從整數類型直接轉換為枚舉類型並稱其為一天。 一旦它是您的標志類型,您就可以毫無問題地使用按位運算符,因此請先執行此操作。
您必須對枚舉執行異或運算符。 因此,如果您的權限值具有:
如果您想刪除 Value4,則必須執行以下操作:
var perm = Permissions.Value1 | Permissions.Value2 | Permissions.Value3 | Permissions.Value4;
perm = perm ^ Permissions.Value4;
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