VB.NET的隐藏功能？

您可以在一行中拥有2行代码.因此:

Dim x As New Something : x.CallAMethod

可以使用#围绕日期来初始化DateTime

Dim independanceDay As DateTime = #7/4/1776#

您还可以使用类型推断和此语法

Dim independanceDay = #7/4/1776#

这比使用构造函数好很多

Dim independanceDay as DateTime = New DateTime(1776, 7, 4)

可选参数

可选项比创建新的重载更容易,例如:

Function CloseTheSystem(Optional ByVal msg AS String = "Shutting down the system...")
   Console.Writeline(msg)
   ''//do stuff
End Function

VB.Net中的标题案例可以通过旧的VB6 fxn来实现:

StrConv(stringToTitleCase, VbStrConv.ProperCase,0) ''0 is localeID

带参数的属性

我一直在做一些C#编程,并发现了一个缺少VB.Net的功能,但这里没有提到.

可以在以下位置看到如何执行此操作的示例(以及c#限制):使用C#中的典型get set属性...带参数

我摘录了该答案的代码:

Private Shared m_Dictionary As IDictionary(Of String, Object) = _
             New Dictionary(Of String, Object)

Public Shared Property DictionaryElement(ByVal Key As String) As Object
    Get
        If m_Dictionary.ContainsKey(Key) Then
            Return m_Dictionary(Key)
        Else
            Return [String].Empty
        End If
    End Get
    Set(ByVal value As Object)
        If m_Dictionary.ContainsKey(Key) Then
            m_Dictionary(Key) = value
        Else
            m_Dictionary.Add(Key, value)
        End If

    End Set
End Property

使用语句堆叠/组合多个:

Dim sql As String = "StoredProcedureName"
Using cn As SqlConnection = getOpenConnection(), _
      cmd As New SqlCommand(sql, cn), _
      rdr As SqlDataReader = cmd.ExecuteReader()

    While rdr.Read()

        ''// Do Something

    End While

End Using

公平地说,你也可以用C#来做.但很多人都不知道这两种语言.

我发现其中一个非常有用且有助于解决许多错误的功能是将参数显式传递给函数,尤其是在使用可选项时.

这是一个例子:

Public Function DoSomething(byval x as integer, optional y as boolean=True, optional z as boolean=False)
' ......
End Function

然后你可以这样称呼它:

DoSomething(x:=1, y:=false)
DoSomething(x:=2, z:=true)
or
DoSomething(x:=3,y:=false,z:=true)

这样更干净,没有bug,然后调用这个函数

DoSomething(1,true)

导入其父级后,子命名空间在范围内.例如,不必导入System.IO或者说System.IO.File来使用File类,你可以说IO.File.这是一个简单的例子:有些地方的功能真的很方便,C#不会这样做.

你可以在一行中有一个If.

If True Then DoSomething()

如果你从来不知道以下内容,你真的不相信它是真的,这真的是C#缺乏时间的东西:

(它被称为XML文字)

Imports 

Module Module1

  Sub Main()
    Dim xml =
      
        
          John
          17
        
        
          Doe
          99
        
      

    Dim id = 1
    Dim name = "Beth"
    DoIt(
      
        
          <%= id %>
          <%= name %>
        
      
    )

    Dim names = xml...
    For Each n In names
      Console.WriteLine(n.Value)
    Next

    For Each customer In xml.
      Console.WriteLine("{0}: {1}", customer.@id, customer..Value)
    Next

    Console.Read()
  End Sub

  Private Sub CreateClass()
    Dim CustomerSchema =
      XDocument.Load(CurDir() & "\customer.xsd")

    Dim fields =
      From field In CustomerSchema...
      Where field.@type IsNot Nothing
      Select
        Name = field.@name,
        Type = field.@type

    Dim customer = 
       Public Class Customer 
<%= From field In fields Select  
Private m_<%= field.Name %> As <%= GetVBPropType(field.Type) %>.Value %>

                     <%= From field In fields Select 
 
Public Property <%= field.Name %> As <%= GetVBPropType(field.Type) %>
 Get 
Return m_<%= field.Name %> 
End Get
 Set(ByVal value As <%= GetVBPropType(field.Type) %>)
 m_<%= field.Name %> = value 
End Set
 End Property
.Value %> 
End Class

    My.Computer.FileSystem.WriteAllText("Customer.vb",
                                        customer.Value,
                                        False,
                                        System.Text.Encoding.ASCII)

  End Sub

  Private Function GetVBPropType(ByVal xmlType As String) As String
    Select Case xmlType
      Case "xs:string"
        Return "String"
      Case "xs:int"
        Return "Integer"
      Case "xs:decimal"
        Return "Decimal"
      Case "xs:boolean"
        Return "Boolean"
      Case "xs:dateTime", "xs:date"
        Return "Date"
      Case Else
        Return "'TODO: Define Type"
    End Select
  End Function

  Private Sub DoIt(ByVal param As XElement)
    Dim customers =
      From customer In param...
      Select New Customer With
      {
        .ID = customer..Value,
        .FirstName = customer..Value
      }

    For Each c In customers
      Console.WriteLine(c.ToString())
    Next
  End Sub

  Private Class Customer
    Public ID As Integer
    Public FirstName As String
    Public Overrides Function ToString() As String
      Return 
ID : <%= Me.ID %>
Name : <%= Me.FirstName %>
             .Value
    End Function

  End Class
End Module
'Results:

ID : 1
Name : Beth
John
Doe
345: 17
365: 99

看看Beth Massi的XML Literals Tips/Tricks.

使用When时精炼错误处理

注意when在行中的使用Catch ex As IO.FileLoadException When attempt < 3

Do
  Dim attempt As Integer
  Try
    ''// something that might cause an error.
  Catch ex As IO.FileLoadException When attempt < 3
    If MsgBox("do again?", MsgBoxStyle.YesNo) = MsgBoxResult.No Then
      Exit Do
    End If
  Catch ex As Exception
    ''// if any other error type occurs or the attempts are too many
    MsgBox(ex.Message)
    Exit Do
  End Try
  ''// increment the attempt counter.
  attempt += 1
Loop

最近在VbRad中查看

这是一个我没见过的有趣的; 我知道它在VS 2008中起作用,至少:

如果你不小心用分号结束你的VB行,因为你做了太多的C#,分号就会被自动删除.实际上不可能(至少在VS 2008中)不小心用分号结束VB行.试试吧!

(它并不完美;如果您在最终的班级名称中间输入分号,则不会自动填写班级名称.)

与breakVB中的C语言不同,您可以Exit或Continue您想要的块:

For i As Integer = 0 To 100
    While True
        Exit While
        Select Case i
            Case 1
                Exit Select
            Case 2
                Exit For
            Case 3
                Exit While
            Case Else
                Exit Sub
        End Select
        Continue For
    End While
Next

在VB8和前面的版本中,如果没有为引入的变量指定任何类型,则自动检测对象类型.在VB9(2008)中,如果Option Infer设置为On(默认情况下),Dim它将像C#的var关键字一样

选择Case代替多个If/ElseIf/Else语句.

在此示例中假设简单的几何对象:

Function GetToString(obj as SimpleGeomertyClass) as String
  Select Case True
    Case TypeOf obj is PointClass
      Return String.Format("Point: Position = {0}", _
                            DirectCast(obj,Point).ToString)
    Case TypeOf obj is LineClass
      Dim Line = DirectCast(obj,LineClass)
      Return String.Format("Line: StartPosition = {0}, EndPosition = {1}", _
                            Line.StartPoint.ToString,Line.EndPoint.ToString)
    Case TypeOf obj is CircleClass
      Dim Line = DirectCast(obj,CircleClass)
      Return String.Format("Circle: CenterPosition = {0}, Radius = {1}", _
                            Circle.CenterPoint.ToString,Circle.Radius)
    Case Else
      Return String.Format("Unhandled Type {0}",TypeName(obj))
  End Select
End Function

与Parsa的答案类似,类似的运算符在简单的通配符之上有很多可以匹配的东西.在阅读MSDN doco时,我几乎摔倒在椅子上:-)

IIf(False, MsgBox("msg1"), MsgBox("msg2"))

结果是什么？两个消息框!!!! 这种情况发生,因为IIf函数在到达函数时会计算两个参数.

VB有一个新的If运算符(就像C#?:运算符):

If(False, MsgBox("msg1"), MsgBox("msg2"))

将仅显示第二个msgbox.

一般情况下,我建议更换你的vb代码中的所有IIF,除非你想要它们两个项目:

Dim value = IIf(somthing, LoadAndGetValue1(), LoadAndGetValue2())

你可以确定两个值都已加载.

如果用[和]括起名称,可以对属性和变量名使用保留关键字

Public Class Item
    Private Value As Integer
    Public Sub New(ByVal value As Integer)
        Me.Value = value
    End Sub

    Public ReadOnly Property [String]() As String
        Get
            Return Value
        End Get
    End Property

    Public ReadOnly Property [Integer]() As Integer
        Get
            Return Value
        End Get
    End Property

    Public ReadOnly Property [Boolean]() As Boolean
        Get
            Return Value
        End Get
    End Property
End Class

'Real examples:
Public Class PropertyException : Inherits Exception
    Public Sub New(ByVal [property] As String)
        Me.Property = [property]
    End Sub

    Private m_Property As String
    Public Property [Property]() As String
        Get
            Return m_Property
        End Get
        Set(ByVal value As String)
            m_Property = value
        End Set
    End Property
End Class

Public Enum LoginLevel
    [Public] = 0
    Account = 1
    Admin = 2
    [Default] = Account
End Enum

在vb.net中声明数组时,始终使用"0到xx"语法.

Dim b(0 to 9) as byte 'Declares an array of 10 bytes

它清楚地表明了数组的跨度.将它与等效物进行比较

Dim b(9) as byte 'Declares another array of 10 bytes

即使你知道第二个例子由10个元素组成,它也感觉不太明显.而且我不记得我从程序员那里看到代码的次数,而不是写的

Dim b(10) as byte 'Declares another array of 10 bytes

这当然是完全错误的.因为b(10)创建一个11字节的数组.并且它很容易导致错误,因为它看起来对任何不知道要寻找什么的人都是正确的.

"0到xx"语法也适用于以下内容

Dim b As Byte() = New Byte(0 To 9) {} 'Another way to create a 10 byte array
ReDim b(0 to 9) 'Assigns a new 10 byte array to b

通过使用完整语法,您还将向将来阅读您的代码的任何人展示您知道自己在做什么.