VB.NET读取数据库时多线程显示进度条

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我是靠谱客的博主冷艳乐曲，这篇文章主要介绍VB.NET读取数据库时多线程显示进度条，现在分享给大家，希望可以做个参考。

VB.net通过ADO.NET连接数据库，或执行查询语句等，都需要等待一段时间，这段时间界面无法操作，程序显示出假死现象，无任何响应，为了不让用户误认为电脑死机，需要显示一个进度条来提示用户。但是问题在于，ADO.NET（包括其它数据库引擎）在执行指令时并不返回实时状态信息，只有在命令执行完毕后，才返回结果。因此，需要通过VB.NET多线程技术，在ADO.NET执行命令期间，显示一个不断变化的进度条，这个进度条是一个单独窗口：
这里写图片描述
窗体命名为TaskProgress，放置一个ProgressBar控件命名为ProgressIndicator，代码如下：

复制代码

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Public Class TaskProgress
Private Sub TaskProgress_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ProgressIndicator.Maximum = 100
ProgressIndicator.Minimum = 0
ProgressIndicator.MarqueeAnimationSpeed = 30
ProgressIndicator.Style = ProgressBarStyle.Marquee
End Sub
End Class

主窗口增加BackgroundWorker组件，此类组件就是用于多线程编程应用的，将其WorkerSupportsCancellation属性设为真(TRUE)，这个属性决定组件是否响应主线程的中断，如图：
这里写图片描述
属性设置：

代码如下：

复制代码

#Region "---------------再开一个线程显示进度条---------------"
Private Sub waitstart()
Me.Cursor = Cursors.WaitCursor
'光标为沙漏
BackgroundWorker1.RunWorkerAsync()
'开启多线程显示进度条
End Sub
Private Sub waitend()
BackgroundWorker1.CancelAsync()
'停止多线程
Me.Cursor = Cursors.Default
'光标为箭头
End Sub
Private Sub BackgroundWorker1_DoWork1(sender As Object, _
e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim worker As System.ComponentModel.BackgroundWorker = _
CType(sender, System.ComponentModel.BackgroundWorker)
' Assign the result of the computation
' to the Result property of the DoWorkEventArgs
' object. This is will be available to the 
' RunWorkerCompleted eventhandler.
showProgress(worker)
End Sub
Private Sub showProgress(ByVal worker As System.ComponentModel.BackgroundWorker)
Dim progressForm As New TaskProgress()
progressForm.Show()
' Refresh causes an instant (non-posted) display of the label.
progressForm.Refresh()
' Slowly increment the progress bar.
While Not worker.CancellationPending
If progressForm.ProgressIndicator.Value = 100 Then
progressForm.ProgressIndicator.Value = 0
Else
progressForm.ProgressIndicator.Value += 10
End If
' 50 millisecond delay
System.Threading.Thread.Sleep(50)
End While
progressForm.ProgressIndicator.MarqueeAnimationSpeed = 0
' Remove the form after the "task" finishes.
progressForm.Hide()
progressForm.Dispose()
End Sub
#End Region

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#Region "---------------再开一个线程显示进度条---------------"
Private Sub waitstart()
Me.Cursor = Cursors.WaitCursor
'光标为沙漏
BackgroundWorker1.RunWorkerAsync()
'开启多线程显示进度条
End Sub
Private Sub waitend()
BackgroundWorker1.CancelAsync()
'停止多线程
Me.Cursor = Cursors.Default
'光标为箭头
End Sub
Private Sub BackgroundWorker1_DoWork1(sender As Object, _
e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim worker As System.ComponentModel.BackgroundWorker = _
CType(sender, System.ComponentModel.BackgroundWorker)
' Assign the result of the computation
' to the Result property of the DoWorkEventArgs
' object. This is will be available to the 
' RunWorkerCompleted eventhandler.
showProgress(worker)
End Sub
Private Sub showProgress(ByVal worker As System.ComponentModel.BackgroundWorker)
Dim progressForm As New TaskProgress()
progressForm.Show()
' Refresh causes an instant (non-posted) display of the label.
progressForm.Refresh()
' Slowly increment the progress bar.
While Not worker.CancellationPending
If progressForm.ProgressIndicator.Value = 100 Then
progressForm.ProgressIndicator.Value = 0
Else
progressForm.ProgressIndicator.Value += 10
End If
' 50 millisecond delay
System.Threading.Thread.Sleep(50)
End While
progressForm.ProgressIndicator.MarqueeAnimationSpeed = 0
' Remove the form after the "task" finishes.
progressForm.Hide()
progressForm.Dispose()
End Sub
#End Region