我有这个大的sql命令,通常返回20 000 – 100 000行数据.
但是只要我调用executeMyQuery函数,程序就会挂起几秒钟,具体取决于返回的大小.
但是只要我调用executeMyQuery函数,程序就会挂起几秒钟,具体取决于返回的大小.
我只返回一列.
如何在运行此命令时显示进度条？
也许在线程或其他东西(我没有线程经验)
这是我的代码(参数是从3个不同的comboBox.selectedItem发送的)：
Public Function executeMyQuery(dbname As String,colname As String,tblname As String)
Try
ListBox1.Items.Clear()
If Not String.IsNullOrWhiteSpace(connString) Then
Using cn As sqlConnection = New sqlConnection(connString)
cn.Open()
Using cmd As sqlCommand = New sqlCommand()
cmd.Connection = cn
Dim qry As String
qry = String.Format("select distinct [{0}] from {1}.dbo.{2} where [{0}] is not null",colname,dbname,tblname)
cmd.CommandText = qry
cmd.CommandTimeout = 0
Dim count As Integer
Using myReader As sqlDataReader = cmd.ExecuteReader()
While (myReader.Read())
count += 1
ListBox1.Items.Add(count.ToString & ". " & myReader.GetString(0))
End While
End Using
End Using
End Using
End If
cn.Close()
Catch ex As Exception
MsgBox("Error Occured : " & ex.Message)
cn.Close()
End
End Function
这是一个如何使用VB.Net 4.0进行Asychrounous工作的简要示例.
原文链接：https://www.f2er.com/vb/255914.html让我们假设您有一个具有以下导入的表单,
Imports System.Windows.Forms Imports System.Threading Imports System.Threading.Tasks
该表格有两个控件
Private WithEvents DoSomthing As Button Private WithEvents Progress As ProgressBar
在你的应用程序的某个地方我们有一个名为ExecuteSlowStuff的函数,这个函数相当于你的executeMyQuery.重要的部分是Action参数,该函数用于显示它正在取得进展.
Private Shared Function ExecuteSlowStuff(ByVal progress As Action) As Integer
Dim result = 0
For i = 0 To 10000
result += i
Thread.Sleep(500)
progress()
Next
Return result
End Function
让我们说这项工作是通过点击DoSomething按钮开始的.
Private Sub Start() Handled DoSomething.Click
Dim slowStuff = Task(Of Integer).Factory.StartNew(
Function() ExceuteSlowStuff(AddressOf Me.ShowProgress))
End Sub
你可能想知道ShowProgress来自哪里,那就是更麻烦的一点.
Private Sub ShowProgress()
If Me.Progress.Invokerequired Then
Dim cross As new Action(AddressOf Me.ShowProgress)
Me.Invoke(cross)
Else
If Me.Progress.Value = Me.Progress.Maximum Then
Me.Progress.Value = Me.Progress.Minimum
Else
Me.Progress.Increment(1)
End If
Me.Progress.Refresh()
End if
End Sub