13518219792
Imports System
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Imports System.Drawing
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Data.OleDb
Imports System.Data
Public Class Form1
Inherits Form
Private components As System.ComponentModel.Container = Nothing
Private WithEvents lastrec As Button
Private WithEvents nextrec As Button
Private WithEvents previousrec As Button
Private WithEvents firstrec As Button
Private t_books As TextBox
Private t_nl As TextBox
Private t_xb As TextBox
Private t_xm As TextBox
Private t_id As TextBox
Private l_books As Label
Private l_nl As Label
Private l_xb As Label
Private l_xm As Label
Private l_id As Label
Private label1 As Label
Private myDataSet As DataSet
Private WithEvents button1 As Button
Private WithEvents button2 As Button
Private WithEvents button3 As Button
Private WithEvents button4 As Button
Private myBind As BindingManagerBase
Public Sub New ( )
MyBase.New ( )
GetConnected ( )
InitializeComponent ( )
End Sub
'清除在程序中使用过的资源
Protected Overloads Overrides Sub Dispose (ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose ( )
End If
End If
MyBase.Dispose ( disposing )
End Sub
Public Sub GetConnected ( )
'创建一个数据连接
Dim strCon As String = " Provider = Microsoft.Jet.OLEDB.4.0 ;
Data Source = db.mdb "
Dim myConn As OleDbConnection = New OleDbConnection ( )
myConn.ConnectionString = strCon
Dim strCom As String = " SELECT * FROM person "
'创建一个 DataSet
myDataSet = New DataSet ( )
myConn.Open ( )
'通过OleDbDataAdapter对象得到一个数据集
Dim myCommand As OleDbDataAdapter = New OleDbDataAdapter
( strCom , myConn )
'把Dataset绑定books数据表
myCommand.Fill ( myDataSet , "person" )
'关闭此数据连接
myConn.Close ( )
End Sub
'插入数据记录操作代码
Private Sub button2_Click (ByVal sender As Object , _
ByVal e As System.EventArgs) Handles button2.Click
'判断所有字段是否添完，添完则执行，反之弹出提示
If ( t_id.Text "" And t_xm.Text ""
And t_xb.Text "" And t_nl.Text ""
And t_books.Text "" ) Then
Dim myConn1 As String = " Provider = Microsoft.Jet.OLEDB.4.0 ;
Data Source = db.mdb"
Dim myConn As OleDbConnection = New OleDbConnection ( myConn1 )
myConn.Open ( )
Dim strInsert As String = " INSERT INTO person ( id , xm , xb , nl
, zip ) VALUES ( " _
t_id.Text + " , '" _
t_xm.Text + "' , '" _
t_xb.Text + "' , " _
t_nl.Text + " , " _
t_books.Text + ")"
Dim inst As OleDbCommand = New OleDbCommand ( strInsert , myConn )
inst.ExecuteNonQuery ( )
myConn.Close ( )
myDataSet.Tables ( "person" ).Rows ( myBind.Position ).BeginEdit ( )
myDataSet.Tables ( "person" ).Rows ( myBind.Position ).EndEdit ( )
myDataSet.Tables ( "person" ).AcceptChanges ( )
Else
MessageBox.Show ( "必须填满所有字段值！" , "错误！" )
End If
End Sub
1.不正确
Dim abc As myClass，定义一个可以引用myClass类型对象的变量abc。这个abc变量存在于栈上。
abc=New myClass。New myClass创建myClass实例对象，这个对象存在于托管堆上。然后（同时）让abc引用（指向）这个对象。
abc变量在栈上，而对象在托管堆上。
abc储存的是对象的地址，而不是对象本身。
看下面的代码
Dim a As myClass,b As myClass,c As myClass
a=New myClass
b=a
c=a
整个过程中只创建了一个myClass对象，位于托管堆上。
三个myClass类型的变量a、b、c位于栈上，都指向了这一个myClass对象
2.类的成员分 实例成员 和 静态成员
实例成员 必须在实例对象上调用
静态成员 可以直接调用，不需要实例对象。
该实例有很多实现方法,下面介绍一种不同的给你:
首先要在窗体中载入以下控件:progressbar(进度条),label(用来实时显示文本提示),两个timer(分别控制进度条进度的增减),然后用以下代码就能实现:
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Timer1.Enabled = True
Timer1.Interval = 500
Timer2.Interval = 500
ProgressBar1.Value = 0
ProgressBar1.Maximum = 100
ProgressBar1.Minimum = 0
End Sub
'上述过程是设置控件的初始值,也可以在属性面板设置
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
ProgressBar1.Value += 1
Label1.Text = "当前完成" ProgressBar1.Value "%"
If (ProgressBar1.Value = 100) Then
Timer1.Enabled = False
Timer2.Enabled = True
End If
End Sub
'timer1用来控制进度的增加
Private Sub Timer2_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer2.Tick
ProgressBar1.Value -= 1
Label1.Text = "当前完成" ProgressBar1.Value "%"
If (ProgressBar1.Value = 0) Then
Timer1.Enabled = True
Timer2.Enabled = False
End If
End Sub
'time2用来控制进度的减少
End Class
