问题描述
我有两节课.
Public Class MainForm
Private Project As clsProject
Private Sub btnDo_Click
...
Backgroundworker.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Project = New clsProject
End Sub
和MainForm中的两个方法
Public Shared Sub setLabelTxt(ByVal text As String, ByVal lbl As Label)
If lbl.InvokeRequired Then
lbl.Invoke(New setLabelTxtInvoker(AddressOf setLabelTxt), text, lbl)
Else
lbl.Text = text
End If
End Sub
Public Delegate Sub setLabelTxtInvoker(ByVal text As String, ByVal lbl As Label)
end class
我想从clsProject构造函数更新MainForm的标签.
MainForm.setLabelTxt("Getting prsadasdasdasdasdry..", MainForm.lblProgress)
,但不会更新它们.我在做什么错了?
您不能直接从BackgroundWorker
对GUI元素执行任何操作.一种克服"的方法是通过Me.Invoke
强制从主线程执行给定的动作;但这不是理想的过程.此外,您的代码混合了主要形式和外部类(+共享/非共享对象),这使整个结构不太牢固.
ProgressChanged Event
.示例代码:Public Class MainForm
Private Project As clsProject
Public Shared bgw As System.ComponentModel.BackgroundWorker
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
bgw = BackgroundWorker1 'Required as far as you want to called it from a Shared method
BackgroundWorker1.WorkerReportsProgress = True
BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Project = New clsProject
End Sub
Public Shared Sub setLabelTxt(ByVal text As String)
bgw.ReportProgress(0, text) 'You can write any int as first argument as far as will not be used anyway
End Sub
Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
Me.Label1.Text = e.UserState 'You can access the given GUI-element directly
Me.Label1.Update()
End Sub
End Class
Public Class clsProject
Public Sub New()
MainForm.setLabelTxt("Getting prsadasdasdasdasdry..")
End Sub
End Class
I have two classes.
Public Class MainForm
Private Project As clsProject
Private Sub btnDo_Click
...
Backgroundworker.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Project = New clsProject
End Sub
and two methods inside MainForm
Public Shared Sub setLabelTxt(ByVal text As String, ByVal lbl As Label)
If lbl.InvokeRequired Then
lbl.Invoke(New setLabelTxtInvoker(AddressOf setLabelTxt), text, lbl)
Else
lbl.Text = text
End If
End Sub
Public Delegate Sub setLabelTxtInvoker(ByVal text As String, ByVal lbl As Label)
end class
I want to update the labels of MainForm from the clsProject constructor.
MainForm.setLabelTxt("Getting prsadasdasdasdasdry..", MainForm.lblProgress)
but it does not update them.What am I doing wrong?
You cannot execute any action on GUI-elements from the BackgroundWorker
directly. One way to "overcome" that is by forcing the given actions to be performed from the main thread via Me.Invoke
; but this is not the ideal proceeding. Additionally, your code mixes up main form and external class (+ shared/non-shared objects) what makes the whole structure not too solid.
A for-sure working solution is relying on the specific BGW methods for dealing with GUI elements; for example: ProgressChanged Event
. Sample code:
Public Class MainForm
Private Project As clsProject
Public Shared bgw As System.ComponentModel.BackgroundWorker
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
bgw = BackgroundWorker1 'Required as far as you want to called it from a Shared method
BackgroundWorker1.WorkerReportsProgress = True
BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Project = New clsProject
End Sub
Public Shared Sub setLabelTxt(ByVal text As String)
bgw.ReportProgress(0, text) 'You can write any int as first argument as far as will not be used anyway
End Sub
Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
Me.Label1.Text = e.UserState 'You can access the given GUI-element directly
Me.Label1.Update()
End Sub
End Class
Public Class clsProject
Public Sub New()
MainForm.setLabelTxt("Getting prsadasdasdasdasdry..")
End Sub
End Class
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