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vb.net语法详解 vbnet implements

IT技术snoozePresse

VB.NET编程语法你这是vb.netvb.net语法详解的代码,vb中不允许那么写:
Dim
strdx()
As
String
=
{"0",
"0",
"0"}
'定义个数组,从后面vb.net语法详解的值能看的出最大下标是2,也就是strdx(0),strdx(1)和strdx(2),3个的默认值都为0
Dim
calcount1
As
String
=
"0"
'定义个字符串变量
Dim
calcount2
As
String
=
"0"
Dim
strvalue
As
Boolean
=
False
'定义strvalue为bool值,改类型变量只有true和false
2种值
If
strdx(0)
=
"0"
Then
TextBox1.Text
=
strdx(0)
"."
这是字符串连接符号,和" "的区别是,他把左右2边的内容直接连接的,而" "可能会编程运算符,例如
2
3
=
"23"
而
2
3
=
5
ElseIf
strvalue
=
False
Then
strdx(0)
=
strdx(0)
"0"
TextBox1.Text
=
strdx(0)
"."
strvalue
=
True
Else
strdx(0)
=
strdx(0)
"0"
TextBox1.Text
=
strdx(0)
Select
Case
calcount1
'
这里开始是分支语句
Case
" "
TextBox1.Text
=
Str(Val(strdx(1))
Val(strdx(0)))
VB.NET语句中continue while的用法VB.NET 2005,已经实现了continue语法，具体是这样操作：
如果 Continue 语句在 Do...Loop 循环中，请将该语句更改为 Continue Do 。
如果 Continue 语句在 For...Next 循环中 ， 请将该语句更改为 Continue For 。
如果 Continue 语句在 While...End While 循环中，请将该语句更改为 Continue While 。
否则，请移除 Continue 语句 。
用法：
For i As Integer = 0 To 100
' If i = 50 跳过 Console.Writeline statement
If i = 50 Then Continue For
Console.WriteLine(i.ToString)
Next
' Do While using Continue statement.
Dim ii As Integer = 1
Do While ii100
ii= 1
' If ii = 50 跳过 Console.Writeline statement
If ii = 50 Then Continue Do
Console.WriteLine(ii.ToString)
Loop
' While using Continue statement.
Dim iii As Integer = 1
While iii100
iii= 1
' If iii = 50 跳过 Console.Writeline statement
If iii = 50 Then Continue While
Console.WriteLine(iii.ToString)
End While
vb.net update语法其他的没法看 ， 不过下面这句是肯定有问题的，应该连编译都过不了：
Dim querystring As String = "update 班级信息表 set 班级名称="TextBox1.Text",班级编号="TextBox2.Text""
改称这样试试：
Dim querystring As String
querystring = "update 班级信息表 set 班级名称="chr(39)TextBox1.Textchr(39)", 班级编号="chr(39)TextBox2.Textchr(39)
如何使用VB.NET中可选参数调用方法VB.NET可选参数的默认值必须是一个常数表达式 。
过程定义中跟在可选参数后的每个参数也都必须是可选的 。
下面的语法显示带VB.NET可选参数的过程声明：
Sub sub name（ByVal parameter 1 As data type 1,
Optional ByVal parameter 2 As data type 2 = default value）
调用带VB.NET可选参数的过程
过程在运行时无法检测到给定的参数是否已被省略，或者调用代码是否已显式提供默认值 。如果需要弄清楚这一点，可以设置一个不可能的值作为默认值 。下面的过程定义了可选参数 office,并测试其默认值 QJZ 以查看它在调用中是否已被省略：
Visual Basic
Sub notify（ByVal company As String, Optional ByVal office As String = "QJZ"）
If office = "QJZ" Then
Debug.WriteLine（"office not supplied -- using Headquarters"）
office = "Headquarters" End If
' Insert code to notify headquarters or specified office.
End Sub
如果可选参数是像 String 这样的引用类型，只要它不是该变量所预期的值 ， 就可以使用 Nothing 作为默认值 。
VB.NET可选参数和重载
定义带可选参数的过程的另一种方法是使用重载 。如果有一个可选参数，可以定义过程的两个重载版本，一个接受此参数，另一个则不带参数 。此方法随可选参数数目的增加而变得更复杂 。然而，这样做的优点是可以完全确定调用程序是否提供了每个VB.NET可选参数 。
vb.net中如何用事件和委托，会C#中的事件和委托，但不知VB.net中的语法，望给个简单的例子熟悉语法 。一委托vb.net语法详解：此示例演示如何将方法与委托关联然后通过委托调用该方法 。
创建委托和匹配过程
创建一个名为 MySubDelegate vb.net语法详解的委托 。
Delegate Sub MySubDelegate(ByVal x As Integer)
声明一个类vb.net语法详解，该类包含与该委托具有相同签名的方法 。
Class class1
Sub Sub1(ByVal x As Integer)
MsgBox("The value of x is: "CStr(x))
End Sub
End Class
定义一个方法，该方法创建该委托的实例并通过调用内置的 Invoke 方法调用与该委托关联的方法 。
Protected Sub DelegateTest()
Dim c1 As New class1
' Create an instance of the delegate.
Dim msd As MySubDelegate = AddressOf c1.Sub1
' Call the method.
msd.Invoke(10)
End Sub
二、事件
下面的示例程序阐释如何在一个类中引发一个事件，然后在另一个类中处理该事件 。AlarmClock 类定义公共事件 Alarm，并提供引发该事件的方法 。AlarmEventArgs 类派生自 EventArgs，并定义 Alarm 事件特定的数据 。WakeMeUp 类定义处理 Alarm 事件的 AlarmRang 方法 。AlarmDriver 类一起使用类，将使用 WakeMeUp 的 AlarmRang 方法设置为处理 AlarmClock 的 Alarm 事件 。
该示例程序使用事件和委托和引发事件中详细说明的概念 。
示例
【vb.net语法详解 vbnet implements】' EventSample.vb.
'
Option Explicit
Option Strict
Imports System
Imports System.ComponentModel
Imports Microsoft.VisualBasic
Namespace EventSample
' Class that contains the data for
' the alarm event. Derives from System.EventArgs.
'
Public Class AlarmEventArgs
Inherits EventArgs
Private _snoozePressed As Boolean
Private nrings As Integer
'Constructor.
'
Public Sub New(snoozePressed As Boolean, nrings As Integer)
Me._snoozePressed = snoozePressed
Me.nrings = nrings
End Sub
' The NumRings property returns the number of rings
' that the alarm clock has sounded when the alarm event
' is generated.
'
Public ReadOnly Property NumRings() As Integer
Get
Return nrings
End Get
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public ReadOnly Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
End Property
' The AlarmText property that contains the wake-up message.
'
Public ReadOnly Property AlarmText() As String
Get
If _snoozePressed Then
Return "Wake Up!!! Snooze time is over."
Else
Return "Wake Up!"
End If
End Get
End Property
End Class
' Delegate declaration.
'
Public Delegate Sub AlarmEventHandler(sender As Object, _
e As AlarmEventArgs)
' The Alarm class that raises the alarm event.
'
Public Class AlarmClock
Private _snoozePressed As Boolean = False
Private nrings As Integer = 0
Private stopFlag As Boolean = False
' The Stop property indicates whether the
' alarm should be turned off.
'
Public Property [Stop]() As Boolean
Get
Return stopFlag
End Get
Set
stopFlag = value
End Set
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
Set
_snoozePressed = value
End Set
End Property
' The event member that is of type AlarmEventHandler.
'
Public Event Alarm As AlarmEventHandler
' The protected OnAlarm method raises the event by invoking
' the delegates. The sender is always this, the current instance
' of the class.
'
Protected Overridable Sub OnAlarm(e As AlarmEventArgs)
RaiseEvent Alarm(Me, e)
End Sub
' This alarm clock does not have
' a user interface.
' To simulate the alarm mechanism it has a loop
' that raises the alarm event at every iteration
' with a time delay of 300 milliseconds,
' if snooze is not pressed. If snooze is pressed,
' the time delay is 1000 milliseconds.
'
Public Sub Start()
Do
nrings= 1
If stopFlag Then
Exit Do
Else
If _snoozePressed Then
System.Threading.Thread.Sleep(1000)
If (True) Then
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
Else
System.Threading.Thread.Sleep(300)
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
End If
Loop
End Sub
End Class
' The WakeMeUp class has a method AlarmRang that handles the
' alarm event.
'
Public Class WakeMeUp
Public Sub AlarmRang(sender As Object, e As AlarmEventArgs)
Console.WriteLine((e.AlarmTextControlChars.Cr))
If Not e.SnoozePressed Then
If e.NumRings Mod 10 = 0 Then
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Press Snooze? Enter N")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
If input.Equals("N") Or input.Equals("n") Then
CType(sender, AlarmClock).SnoozePressed = True
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End If
Else
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End Sub
End Class
' The driver class that hooks up the event handling method of
' WakeMeUp to the alarm event of an Alarm object using a delegate.
' In a forms-based application, the driver class is the
' form.
'
Public Class AlarmDriver
Public Shared Sub Main()
' Instantiates the event receiver.
Dim w As New WakeMeUp()
' Instantiates the event source.
Dim clock As New AlarmClock()
' Wires the AlarmRang method to the Alarm event.
AddHandler clock.Alarm, AddressOf w.AlarmRang
clock.Start()
End Sub
End Class
End Namespace
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