[英]C# flag enum toggle by value or name
我有一个 Flags enum
,想通过它的 ( long
) 值来切换一些值。
[Flags]
public enum Permissions : long
{
Value0 = 0,
Value1 = 0x1,
Value2 = 0x2,
Value3 = 0x4,
//etc
}
我使用long
字段通过EF
将实际权限存储在数据库中,例如:
public Permissions UsersPermissions { get; set; }
从客户端,我一一获取值以通过enum
切换正确的值,因此如果数据库字段包含
`Value1 | Value2 | Value3`
我得到 4 我必须从用户的权限中删除 Value3。
enum
值? 我已经尝试过usersPermissions |= permissionValue
但它说我不能在long
和Permission
Types 上使用|=
运算符。
您必须在适当的点对long
和Permissions
进行一些转换,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
这里重要的是~toRemove
返回~toRemove
的按位补toRemove
,从而为您提供一组位标志,您可以使用原始值&
以关闭在toRemove
中设置的所有位。
你必须投perms
到long
,以做到这一点&
操作。
最后,通过&
获得所需的结果后,您必须将long
回Permissions
以获得正确的枚举类型作为最终答案。
据我所知,您的输入是一个数字,您希望它是一个Permissions
。 好吧,即使它不是离散值之一,您也可以直接转换它。 如果它是标志值之一的组合,那甚至可以“弄清楚”。 C# 枚举以这种方式进行强制转换非常聪明。
这是一个代码示例,可以执行您想要的操作
[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);
}
这是通过最后一个元素的值获得枚举限制的方法:
{
// 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);
}
输出:
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
我完全承认上面可能有更好的方法,但从根本上说,如果您有一个[Flags]
枚举,因此其中的所有内容在一定程度上都是“有效的”(所有组合都可以),只需检查是否您的值超出范围,然后将其从整数类型直接转换为枚举类型并称其为一天。 一旦它是您的标志类型,您就可以毫无问题地使用按位运算符,因此请先执行此操作。
您必须对枚举执行异或运算符。 因此,如果您的权限值具有:
如果您想删除 Value4,则必须执行以下操作:
var perm = Permissions.Value1 | Permissions.Value2 | Permissions.Value3 | Permissions.Value4;
perm = perm ^ Permissions.Value4;
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