Question

我在内部应用程序上使用.Net Reflector来尝试理解之前的Dev正在做什么以及学习。我从来没有关于如何开发应用程序的实际指令，所以我从可以的地方采取（Hooray Stack Overflow）。话虽如此，我发现了让我困惑的事情。一个名为WinConstant的类库，包含以下代码。

以下是我的实际问题：

这可能有什么用处？
存储a有什么价值一堆常数库中？
这被认为是“最好的实践“？

赞赏的想法和指导！


Public Class clsConstant
    Public Const cAccess As String = "Access"
    Public Const cAddress As String = "Address"
    Public Const cCancel As String = "Cancel"
    Public Const cCity As String = "City"
    Public Const cClear As String = "Clear"
    Public Const cClickOnMessage As String = "Click on any row in top pane to see the detail fields in the bottom pane."
    Public Const cClientID As String = "ClientID"
    Public Const cColon As String = ": "
    Public Const cComma As String = ","
    Public Const cContactID As String = "ContactID"
    Public Const cCounty As String = "County"
    Public Const cDash As String = "-"
    Public Const cDelete As String = "Delete"
    Public Const cDepartment As String = "Department"
    Public Const cError As String = "Error"
    Public Const cExec As String = "Exec"
    Public Const cFalse As String = "False"
    Public Const cFavorite As String = "Favorite"
    Public Const cFederal As String = "Federal"
    Public Const cFriday As String = "Friday"
    Public Const cfrmMain As String = "frmMain"
    Public Const cfrmModuleLogin As String = "frmModuleLogin"
    Public Const cfrmModuleSplash As String = "frmModuleSplash"
    Public Const cHelp As String = "Help"
    Public Const cHint As String = "Hint"
    Public Const cImagePath As String = "../../image"
    Public Const cIn As String = "In"
    Public Const cInformation As String = "Information"
    Public Const cInitialScreenID As String = "InitialScreenID"
    Public Const cInsert As String = "Insert"
    Public Const cJuvenileID As String = "JuvenileID"
    Public Const cLetter As String = "Letter"
    Public Const cManual As String = "Manual"
    Public Const cMasterID As String = "MasterID"
    Public Const cModuleID As String = "ModuleID"
    Public Const cModuleName As String = "ModuleName"
    Public Const cMonday As String = "Monday"
    Public Const cName As String = "Name"
    Public Const cNegative As String = "Negative"
     _
    Public Shared ReadOnly cNLowDate As DateTime = New DateTime(&H851055320574000)
     _
    Public Shared ReadOnly cNullDate As DateTime = New DateTime
    Public Const cNullDateString As String = "12:00:00 AM"
    Public Const cOfficeIDDefault As String = "01"
    Public Const cOne As Integer = 1
    Public Const cOut As String = "Out"
    Public Const cPopUp As String = "PopUp"
    Public Const cPositive As String = "Positive"
    Public Const cProcess As String = "Process"
    Public Const cProviderID As String = "ProviderID"
    Public Const cQuestion As String = "Question"
    Public Const cRead As String = "Read"
    Public Const cReferralID As String = "ReferralID"
    Public Const cReminder As String = "Reminder"
    Public Const cReport As String = "Report"
    Public Const cReportEngine As String = "ReportEngine"
    Public Const cReportEnginePath As String = "ReportEnginePath"
    Public Const cReportingServices As String = "ReportingServices"
    Public Const cReportServer As String = "ReportServer"
    Public Const cReportService As String = "ReportService"
    Public Const cReportServiceLocal As String = "ReportServiceLocal"
    Public Const cReportServiceServer As String = "ReportServiceServer"
    Public Const cSaturday As String = "Saturday"
    Public Const cSearch As String = "Search"
    Public Const cSelect As String = "Select"
    Public Const cSpace As String = " "
    Public Const cSQLLoginError As String = "SQL Server login/password invalid"
    Public Const cStart As String = "Select a module"
    Public Const cState As String = "State"
    Public Const cSubjectID As String = "SubjectID"
    Public Const cSunday As String = "Sunday"
    Public Const cThursday As String = "Thursday"
    Public Const cTooltipCancel As String = "Reset form data values back to before all manual changes."
    Public Const cTooltipClear As String = "Clears all data entry fields prior to an Insert"
    Public Const cTooltipClient As String = "Display a Client popup window."
    Public Const cTooltipClose As String = "Close this form"
    Public Const cTooltipDelete As String = "Delete the current record being displayed, no undo possible."
    Public Const cTooltipExe As String = "Initiate a batch process."
    Public Const cTooltipInsert As String = "Insert a brand new record"
    Public Const cTooltipSearch As String = "Perform a Search for values entered."
    Public Const cTooltipSelect As String = "Perform a Select for values entered."
    Public Const cTooltipUpdate As String = "Update an existing record"
    Public Const cTrue As String = "True"
    Public Const cTuesday As String = "Tuesday"
    Public Const cUnderscore As String = "____________________________________________________________"
    Public Const cUpdate As String = "Update"
    Public Const cWarning As String = "Warning"
    Public Const cWeb As String = "Web"
    Public Const cWednesday As String = "Wednesday"
    Public Const cWorkerID As String = "WorkerID"
    Public Const cZero As Integer = 0
    Public Shared strLongDate As String() = DateAndTime.Now.ToLongDateString.Split(New Char() { ","c })
    Public Shared strModuleMainStatusStripFormID As String = Nothing
End Class

Answer 1

回到用c编码windows应用程序的时代，在Windows中有类似的文件#included包含 long #defines创建常量列表。各种c应用程序在自己的文件中模拟了这种方法。 “阶级”似乎是这种“c-ism”的“音译”。面向对象设计的基本原则是将代码和数据混合到相关的功能单元：对象中。正如jfullerton写道：

从编程的角度来看，面向对象涉及程序对象，封装，继承，和多态性。概念对象在程序中建模码。封装保持一个对象使用数据的数据和方法作为对象的一部分。

很明显，这个常数列表不符合OO实践，但是回归过去。

回答你的问题：

- 此类包含常量，即
- 老开发者可能这样做是因为那是他以前做的事情
- 这不是当前的最佳做法。

当然，如果这是你的应用程序的一部分，你不能把它扔掉。相反，假设您使用Test Driven Development和Refactoring

当前

Answer 2

将文字与其余代码分开是一个好主意。

奇怪的是，这些应该主要是资源而不是常量字符串。然后，如果需要，可以轻松地对其进行本地化，或者在不重新编译整个应用程序的情况下替换/更新。

其中一些甚至不是资源：cUnderscore例如看起来像使用文本来创建视觉效果 - 通常是一个坏主意。

在你的前任的辩护中，我认为这个代码比寻找分散在整个源代码中的相同常量更为可取，因为它会使资源的重构变得更简单。

Answer 3

常量永远不会改变，例如

Public Const NumberOne as Int = 1

所以这是我的第一句话：你总结的一些东西并不是真的。

另一个缺点是使用const关键字会创建二进制依赖项。这意味着您将不得不重建使用constants.dll的程序集。你不能只是替换它。这是由consts的工作方式引起的：编译器在编译时用替换名称。

此问题的解决方案是使用ReadOnly而不是Const。

我认为创建这样的库并不是一个好习惯。我不允许我的团队创建一个......

Answer 4

这看起来像开发人员有一个编码标准，说：不要在代码中使用字符串文字，并尽职尽责地将每个常量分开，无论它是否有意义。

例如，可能有一些元素需要代码中的数字1，而不是使用DefaultNumberOfLineItems或其他一些描述性常量，它们使用NumberOne = 1;

最佳做法是保持常量描述并接近其使用点。静态类的相关常量没有任何问题，这些常量具有某种类型的含义并且彼此相关。

例如，有一个系统我使用了唯一键来处理标签属性。这些键收集在静态类中，在属性上具有描述性名称，实际键由自动化系统生成

public static class AttributeIDs
{
   public const string Name = "UniqueGeneratedKeyForNameAttribute";
   public const string Description ="UnqiueGeneratedKeyForDescriptionAttribute";
   ... etc.
}

在实践中，这就像

一样使用

MyAccess.GetValueForAttribute(AttributeIDs.Name);

将所有相关常数放在一起。

Answer 5

这类课程可能有用。通常，诸如“幻数”或“魔术字符串”之类的内容会被转换为常量并放置在静态（共享）类中。这样做的原因是将这些“魔术”值隔离到一个位置，并允许它们被有意义的名称引用。（通常用于数值。）对于字符串值，它有助于确保每次都使用相同的值引用事物。最好的例子是你的app.config文件中的字符串键。

话虽这么说，常量应该用于不改变的东西（或者很少改变，它实际上是不变的）。在大多数情况下，可能会更改（或需要本地化）的字符串应作为资源存储在.resx文件中。

Answer 6

拥有一个常量类库是没有错的。常数是一种很好的习惯。毕竟，枚举在.NET中占有一席之地，它们只是数组常量。依赖于常量程序集与任何其他依赖项没有什么不同。理解常量的目的更多的是关于应用程序的逻辑。我的猜测是这些常量可以启用详细日志记录，而无需使用一堆字符串文字填充应用程序。

Answer 7

它看起来像是一个字符串表的天真实现。

这些值不是魔术字符串和“简单”的系统范围更改。我认为资源文件更容易实现和维护。

您同事的实施是最佳做法吗？我会说不。使用字符串表，特别是如果您需要在应用程序中进行国际化。

Answer 8

在许多情况下，将字符串常量放入单独的类中是最佳实践，但是，这是一个糟糕的例子。更好的方法是创建一个StringConstants命名空间，然后组织字符串，以便将相关的字符串常量组织成单独的类。这只是一个好主意的糟糕实现。

如果全球化是一个问题，那么（正如其他人所指出的那样），字符串应保存在资源文件中。

Answer 9

我们这样做是为了从代码库中分离出数据库特定的常量。这种解耦使我们可以在将来更新数据库（当前的MS Access）以更好地（可能是SQL Server）而不必更改大量的代码库。以下是特定于表的常量块的示例：

    Public Class Equalisations
    Public Const TableName As String = "Equalisations"
    Public Class SPs
        Public Const SelectAll As String = General.SPs.Prefix & TableName & General.SPs.SelectAll
        Public Const SelectDropDownList As String = General.SPs.Prefix & TableName & General.SPs.SelectDropDownList
        Public Const SelectAllChildRecords As String = General.SPs.Prefix & TableName & General.SPs.SelectAllChildRecords
        Public Const SelectRecord As String = General.SPs.Prefix & TableName & General.SPs.SelectRecord
        Public Const SelectMaxId As String = General.SPs.Prefix & TableName & General.SPs.SelectMaxId
        Public Const InsertRecord As String = General.SPs.Prefix & TableName & General.SPs.InsertRecord
        Public Const DeleteAllRecords As String = General.SPs.Prefix & TableName & "_DeleteAllRecords"
    End Class
    Public Class Cols
        Public Const CompanyAccountID As String = "CitiAccountID"
        Public Const NAVDate As String = "NAVDate"
        Public Const GLCodeID As String = "GLCodeID"
        Public Const Income As String = "Income"
        Public Const LoadedFileID As String = "LoadedFileID"
    End Class
    Public Class Parms
        Public Const CompanyAccountID As String = "pCitiAccountID"
        Public Const NAVDate As String = "pNAVDate"
        Public Const GLCodeID As String = "pGLCodeID"
        Public Const Income As String = "pIncome"
        Public Const LoadedFileID As String = "pLoadedFileID"
    End Class
End Class

Answer 10

我能想到的唯一解释是某种消息库 - 但这并不适用于90％的条目。

例如，这只是愚蠢的：

 Public Const cInsert As String = "Insert"

这闻起来非常糟糕。

Answer 11

c＃中有两种类型的常量：编译时常量和运行时常量。他们有不同的行为和使用错误的将花费你的性能或正确性。所以选择适合你的项目使用的常量类型..

http://dotnetacademy.blogspot.com/2011/09/constants-in-net.html

常数类库 - 最佳实践？

11 个答案: