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本篇文章為大家展示了如何在ASP.Net Core中使用枚舉類，內容簡明扼要并且容易理解，絕對能使你眼前一亮，通過這篇文章的詳細介紹希望你能有所收獲。
一、通常我們是這樣使用枚舉的
（1）switch中使用枚舉
public enum EmployeeType
{
Manager,
Servant,
AssistantToTheRegionalManager
}public class Employee
{
public EmployeeType Type { get; set; }
public decimal Bonus { get; set; }
}static void ProcessBonus(Employee employee)
{
switch (employee.Type)
{
case EmployeeType.Manager:
employee.Bonus = 1000m;
break;
case EmployeeType.Servant:
employee.Bonus = 0.01m;
break;
case EmployeeType.AssistantToTheRegionalManager:
employee.Bonus = 1.0m;
break;
default:
throw new ArgumentOutOfRangeException();
}
}在沒有進某唐時我也是這樣的寫的，代碼很爛，違法了開閉原則，擴展性極差。在代碼規范中是不允許出現這樣的寫法的。對于上面的寫法可以使用設計模式來重構。后面會繼續更新設計模式的文章。
（2）類型轉換
EnumTricks.IsVolumeHigh((Volume)27); EnumTricks.High((int)Medium);
二、枚舉的不好之處
關于枚舉的MSDN文檔說了什么：
“The enum keyword is used to declare an enumeration, a distinct type that consists of a set of named constants called the enumerator list. Every enumeration type has an underlying type, which can be any integral type except char. The default underlying type of the enumeration elements is int. By default, the first enumerator has the value 0, and the value of each successive enumerator is increased by 1.
（1）沒有類型安全
枚舉是簡單的值類型，可以提供對無效值的保護，并且不會出現任何行為。他們是有用的，因為他們是魔法數字的改進，但就是這樣。如果要約束類型可能的值，枚舉不一定能幫助您，因為仍然可以提供無效類型。例如，此枚舉有三個值，默認情況下將具有int類型。值范圍為1到3。
public enum Volume
{
Low = 1,
Medium,
High
}public static class EnumTricks
{
public static bool IsVolumeHigh(Volume volume)
{
var result = false;
switch (volume)
{
case Volume.Low:
Console.WriteLine("Volume is low.");
break;
case Volume.Medium:
Console.WriteLine("Volume is medium.");
break;
case Volume.High:
Console.WriteLine("Volume is high.");
result = true;
break;
}
return result;
}
}static void Main(string[] args)
{
EnumTricks.IsVolumeHigh((Volume)27);
Console.ReadKey();
}public static class EnumTricks
{
public static bool IsVolumeHigh(Volume volume)
{
var result = false;
switch (volume)
{
case Volume.Low:
Console.WriteLine("Volume is low.");
break;
case Volume.Medium:
Console.WriteLine("Volume is medium.");
break;
case Volume.High:
Console.WriteLine("Volume is high.");
result = true;
break;
}
return result;
}
public static int EnumToInt(Volume volume)
{
return (int)volume;
}
public static Volume IntToEnum(int intValue)
{
return (Volume)intValue;
}
public static Volume StringToEnum(string stringValue)
{
return (Volume)Enum.Parse(typeof(Volume), stringValue);
}
public static int StringToInt(string stringValue)
{
var volume = StringToEnum(stringValue);
return EnumToInt(volume);
}
public static string EnumToString(Volume volume)
{
return volume.ToString();
}
}這應該失敗，至少在運行時。它沒有。這真的很奇怪......在編譯期間或運行期間都不會檢測到錯誤的調用。你會覺得自己處于一個虛假的安全狀態。如果，我們把傳進去的枚舉轉換為string時，來看看這兩種情況有什么不同：
我不知道大家平時在使用枚舉的時候，是否有意識檢查傳入的是否是有效的值。可以使用Enum.IsDefined()來檢查int值是否是一個有效的值
解決方案：如果int值在枚舉值的定義范圍內，則使用Enum.IsDefined()查找。如果在范圍內，則返回True，否則返回False。
（2）轉化
您是否嘗試過將enum轉換為int，int轉換為enum，string轉換為enum，將字符串轉換為enum的int值？如下代碼：
public static class EnumTricks
{
public static bool IsVolumeHigh(Volume volume)
{
var result = false;
switch (volume)
{
case Volume.Low:
Console.WriteLine("Volume is low.");
break;
case Volume.Medium:
Console.WriteLine("Volume is medium.");
break;
case Volume.High:
Console.WriteLine("Volume is high.");
result = true;
break;
}
return result;
}
public static int EnumToInt(Volume volume)
{
return (int)volume;
}
public static Volume IntToEnum(int intValue)
{
return (Volume)intValue;
}
public static Volume StringToEnum(string stringValue)
{
return (Volume)Enum.Parse(typeof(Volume), stringValue);
}
public static int StringToInt(string stringValue)
{
var volume = StringToEnum(stringValue);
return EnumToInt(volume);
}
}是不是我們日常的代碼中也有這樣的類型轉換代碼，不是說不好，只是類型轉換也是有性能損失的，如果能換中方式可以同樣實現而且還避免以上問題豈不是更好，這樣我們的代碼也更好維護和擴展，下面我們通過使用枚舉類的方式來解決這個問題。
三、使用枚舉類而不是枚舉類型
public class Enumeration: IComparable
{
private readonly int _value;
private readonly string _displayName;
protected Enumeration()
{
}
protected Enumeration(int value, string displayName)
{
_value = value;
_displayName = displayName;
}
public int Value
{
get { return _value; }
}
public string DisplayName
{
get { return _displayName; }
}
public override string ToString()
{
return DisplayName;
}
public static IEnumerable<T> GetAll<T>() where T : Enumeration, new()
{
var type = typeof(T);
var fields = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly);
foreach (var info in fields)
{
var instance = new T();
var locatedValue = info.GetValue(instance) as T;
if (locatedValue != null)
{
yield return locatedValue;
}
}
}
public override bool Equals(object obj)
{
var otherValue = obj as Enumeration;
if (otherValue == null)
{
return false;
}
var typeMatches = GetType().Equals(obj.GetType());
var valueMatches = _value.Equals(otherValue.Value);
return typeMatches && valueMatches;
}
public override int GetHashCode()
{
return _value.GetHashCode();
}
public static int AbsoluteDifference(Enumeration firstValue, Enumeration secondValue)
{
var absoluteDifference = Math.Abs(firstValue.Value - secondValue.Value);
return absoluteDifference;
}
public static T FromValue<T>(int value) where T : Enumeration, new()
{
var matchingItem = parse<T, int>(value, "value", item => item.Value == value);
return matchingItem;
}
public static T FromDisplayName<T>(string displayName) where T : Enumeration, new()
{
var matchingItem = parse<T, string>(displayName, "display name", item => item.DisplayName == displayName);
return matchingItem;
}
private static T parse<T, K>(K value, string description, Func<T, bool> predicate) where T : Enumeration, new()
{
var matchingItem = GetAll<T>().FirstOrDefault(predicate);
if (matchingItem == null)
{
var message = string.Format("'{0}' is not a valid {1} in {2}", value, description, typeof(T));
throw new ApplicationException(message);
}
return matchingItem;
}
public int CompareTo(object other)
{
return Value.CompareTo(((Enumeration)other).Value);
}
}public class Volume: Enumeration
{
private Volume() { throw new Exception(""); }
private Volume(int value, string displayName): base(value, displayName) { }
public static readonly Volume Low = new Volume(1, nameof(Low).ToLowerInvariant());
public static readonly Volume Medium = new Volume(2, nameof(Medium).ToLowerInvariant());
public static readonly Volume High = new Volume(3, nameof(High).ToLowerInvariant());
public static IEnumerable<Volume> List() =>
new[] { Low, Medium, High };
public static Volume From(int value)
{
var state = List().SingleOrDefault(s => s.Value == value);
if (state == null)
{
throw new Exception($"Possible values for Volume: {String.Join(",", List().Select(s => s.Value))}");
}
return state;
}
public static Volume FromName(string name)
{
var state = List()
.SingleOrDefault(s => String.Equals(s.DisplayName, name, StringComparison.CurrentCultureIgnoreCase));
if (state == null)
{
throw new Exception($"Possible values for Volume: {String.Join(",", List().Select(s => s.DisplayName))}");
}
return state;
}
}static void Main(string[] args)
{
//EnumTricks.IsVolumeHigh((Volume)27);
//var tmp = Enum.IsDefined(typeof(Volume), 3);
//var str = EnumTricks.EnumToString((Volume)27);
//var str2 = EnumTricks.EnumToString((Volume)3);
//Console.WriteLine($"Volume 27:{str}");
//Console.WriteLine($"Volume 3:{str2}");
Console.WriteLine("------------------------------------------------------------");
Console.WriteLine(Volume.High.Value);
Console.WriteLine(Volume.High.DisplayName);
var volume = Volume.From(2);
var volume2 = Volume.FromName("high");
var none = Volume.From(27);
Console.ReadKey();
}四、應用
代碼如下：
Error文件下：
public interface ICommonError
{
int GetErrCode();
string GetErrMsg();
ICommonError SetErrMsg(string errMsg);
}public class Enumeration : IComparable
{
private readonly int _value;
private readonly string _displayName;
protected Enumeration()
{
}
protected Enumeration(int value, string displayName)
{
_value = value;
_displayName = displayName;
}
public int Value
{
get { return _value; }
}
public string DisplayName
{
get { return _displayName; }
}
public override string ToString()
{
return DisplayName;
}
public static IEnumerable<T> GetAll<T>() where T : Enumeration, new()
{
var type = typeof(T);
var fields = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly);
foreach (var info in fields)
{
var instance = new T();
var locatedValue = info.GetValue(instance) as T;
if (locatedValue != null)
{
yield return locatedValue;
}
}
}
public override bool Equals(object obj)
{
var otherValue = obj as Enumeration;
if (otherValue == null)
{
return false;
}
var typeMatches = GetType().Equals(obj.GetType());
var valueMatches = _value.Equals(otherValue.Value);
return typeMatches && valueMatches;
}
public override int GetHashCode()
{
return _value.GetHashCode();
}
public static int AbsoluteDifference(Enumeration firstValue, Enumeration secondValue)
{
var absoluteDifference = Math.Abs(firstValue.Value - secondValue.Value);
return absoluteDifference;
}
public static T FromValue<T>(int value) where T : Enumeration, new()
{
var matchingItem = parse<T, int>(value, "value", item => item.Value == value);
return matchingItem;
}
public static T FromDisplayName<T>(string displayName) where T : Enumeration, new()
{
var matchingItem = parse<T, string>(displayName, "display name", item => item.DisplayName == displayName);
return matchingItem;
}
private static T parse<T, K>(K value, string description, Func<T, bool> predicate) where T : Enumeration, new()
{
var matchingItem = GetAll<T>().FirstOrDefault(predicate);
if (matchingItem == null)
{
var message = string.Format("'{0}' is not a valid {1} in {2}", value, description, typeof(T));
throw new ApplicationException(message);
}
return matchingItem;
}
public int CompareTo(object other)
{
return Value.CompareTo(((Enumeration)other).Value);
}
}public class EmBusinessError : Enumeration, ICommonError
{
private int errCode;
private String errMsg;
public static readonly EmBusinessError parameterValidationError = new EmBusinessError(10001, "參數不合法");
private EmBusinessError() { throw new Exception("私有構造函數不能調用"); }
private EmBusinessError(int value, string displayName) : base(value, displayName) {
this.errCode = value;
this.errMsg = displayName;
}
public int GetErrCode()
{
return this.errCode;
}
public string GetErrMsg()
{
return this.errMsg;
}
public void SetErrCode(int errCode)
{
this.errCode = errCode;
}
public ICommonError SetErrMsg(string errMsg)
{
this.errMsg = errMsg;
return this;
}
}//包裝器業務異常類實現
public class BusinessException : Exception, ICommonError
{
private ICommonError commonError;
//直接接收EmBusinessError的傳參用于構造業務異常
public BusinessException(ICommonError commonError):base()
{
this.commonError = commonError;
}
public BusinessException(ICommonError commonError, string errMsg):base()
{
this.commonError = commonError;
this.commonError.SetErrMsg(errMsg);
}
public int GetErrCode()
{
return this.commonError.GetErrCode();
}
public string GetErrMsg()
{
return this.commonError.GetErrMsg();
}
public ICommonError SetErrMsg(string errMsg)
{
this.commonError.SetErrMsg(errMsg);
return this;
}
public ICommonError GetCommonError()
{
return commonError;
}
}異常中間件：
public class ExceptionHandlerMiddleWare
{
private readonly RequestDelegate next;
/// <summary>
///
/// </summary>
/// <param name="next"></param>
public ExceptionHandlerMiddleWare(RequestDelegate next)
{
this.next = next;
}
public async Task Invoke(HttpContext context)
{
try
{
await next(context);
}
catch (Exception ex)
{
await HandleExceptionAsync(context, ex);
}
}
private static async Task HandleExceptionAsync(HttpContext context, Exception exception)
{
if (exception == null) return;
await WriteExceptionAsync(context, exception).ConfigureAwait(false);
}
private static async Task WriteExceptionAsync(HttpContext context, Exception exception)
{
var response = context.Response;
response.ContentType = "application/json;charset=utf-8";
var result = new CommonReturnType();
if (exception is BusinessException)
{
var businessException = (BusinessException)exception;
var errModel = new { errCode= businessException.GetErrCode(), errMsg= businessException.GetErrMsg() };
result = CommonReturnType.Create(errModel, "fail");
}
await response.WriteAsync(JsonConvert.SerializeObject(new { data = result.GetData(), status = result.GetStatus() }) ).ConfigureAwait(false);
}
}Response文件夾：
public class CommonReturnType
{
//表明對應請求的返回處理結果 "success" 或 "fail"
private string status;
//若status=success,則data內返回前端需要的json數據
//若status=fail，則data內使用通用的錯誤碼格式
private object data;
//定義一個通用的創建方法
public static CommonReturnType Create(object result)
{
return CommonReturnType.Create(result, "success");
}
public static CommonReturnType Create(object result, string status)
{
CommonReturnType type = new CommonReturnType();
type.SetStatus(status);
type.SetData(result);
return type;
}
public string GetStatus()
{
return status;
}
public void SetStatus(string status)
{
this.status = status;
}
public object GetData()
{
return data;
}
public void SetData(object data)
{
this.data = data;
}
}ASP.NET 是開源，跨平臺，高性能，輕量級的 Web 應用構建框架，常用于通過 HTML、CSS、JavaScript 以及服務器腳本來構建網頁和網站。
上述內容就是如何在ASP.Net Core中使用枚舉類，你們學到知識或技能了嗎？如果還想學到更多技能或者豐富自己的知識儲備，歡迎關注億速云行業資訊頻道。
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