跨线程操作无效... - VB.NET

Question

我正在使用 vb.net，在我的程序中，当我运行后台工作程序时，我会收到此“跨线程操作无效”错误，这将使此文本框启用为 true。我的主子程序将首先将启用设置为 false，当后台工作程序运行时，它会将其设置为 true，然后退出。为什么它给我一个错误？仅供参考：还有更多代码，但我不想让它变得更加混乱......

这是堆栈跟踪：

at System.Windows.Forms.Control.get_Handle()
   at System.Windows.Forms.Control.OnEnabledChanged(EventArgs e)
   at System.Windows.Forms.Control.set_Enabled(Boolean value)
   at Helium.Form1.BackgroundWorker1_DoWork(Object sender, DoWorkEventArgs e) in C:\Users\Kevin\documents\visual studio 2010\Projects\Helium\Helium\Form1.vb:line 167
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

这是确切的错误消息：

{"Cross-thread operation not valid: Control 'mainText' accessed from a thread other than the thread it was created on."}

有人可以帮帮我吗！

谢谢，

凯文

Answer 1

BackgroundWorker

类的目的是在非GUI线程上执行工作，同时GUI保持响应。除非您将

Control.CheckForIllegalCrossThreadCalls

设置为

false

（您不应该这样做），或者按照其他答案中的建议使用

Invoke

（我也不推荐），否则您将获得非法交叉线程操作异常。

如果您希望在 BackgroundWorker 运行时发生与 GUI 相关的“事情”，我通常建议使用

BackgroundWorker.ReportProgress

方法并将适当的处理程序附加到

BackgroundWorker.ProgressChanged

事件。如果您希望在

BackgroundWorker

finished

后 GUI 上发生某些事情，则只需附加处理程序即可将 GUI 更新到 BackgroundWorker.RunWorkerCompleted 事件。

Answer 2

Enabled

属性？如果您在

DoWork

事件处理程序中执行此操作，则此代码将在与创建按钮不同的线程上运行，这应该会给出您遇到的异常。要解决这个问题，您应该使用

BeginInvoke

。为了方便起见，可以将其包装到一个方法中，如下所示：

Private Sub SetControlEnabled(ByVal ctl As Control, ByVal enabled As Boolean)
    If ctl.InvokeRequired Then
        ctl.BeginInvoke(New Action(Of Control, Boolean)(AddressOf SetControlEnabled), ctl, enabled)
    Else
        ctl.Enabled = enabled
    End If
End Sub

现在您可以安全地调用该方法来启用或禁用任何线程的任何控件：

SetControlEnabled(someButton, False)

Answer 3

Form1_Load

（或任何您的表单）子中键入以下代码：

System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = False

它修复了所有阻塞跨线程操作的问题。

Answer 4

Extension

它为跨线程 GUI 控制调用编写了非常漂亮的代码。

只需将这行代码添加到您拥有的任何模块中即可。

<System.Runtime.CompilerServices.Extension()> _
Public Sub Invoke(ByVal control As Control, ByVal action As Action)
    If control.InvokeRequired Then
        control.Invoke(New MethodInvoker(Sub() action()), Nothing)
    Else
        action.Invoke()
    End If
End Sub

现在您可以编写任何控制调用都只有 1 行长的跨线程控制代码。

像这样，假设您想清除一个组合框，并且它是从线程调用的，或者没有线程，您现在就可以使用它

cboServerList.Invoke(Sub() cboServerList.Items.Clear())

清除后还想添加一些东西吗？

cboServerList.Invoke(Sub() cboServerList.Items.Add("Hello World"))

Answer 5

Private Sub SetText(ByVal [text] As String)

    ' InvokeRequired required compares the thread ID of the'
    ' calling thread to the thread ID of the creating thread.'
    ' If these threads are different, it returns true.'
    If Me.textBox1.InvokeRequired Then
        Dim d As New SetTextCallback(AddressOf SetText)
        Me.Invoke(d, New Object() {[text]})
    Else
        Me.textBox1.Text = [text]
    End If
End Sub

Answer 6

'## crossed-thread parts will not be controlled by this option...

System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = False

Answer 7

例如，当我按 F5 键时，下面的代码调用执行按钮。同样，如果您希望线程或后台工作人员调用事件或函数，您可以使用 Automation Peer。在您的情况下，您可以使用文本框及其适当的属性来调用，而不是按钮（我在这里使用的）。

'Button name=btnExecute

'Imports System.Windows.Automation.Peers

'Imports System.Windows.Automation.Provider

If e.Key = Key.F5 Then

   Dim peer As New ButtonAutomationPeer(btnExecute)

   Dim invokeProv As IInvokeProvider = TryCast(peer.GetPattern(PatternInterface.Invoke), IInvokeProvider)

   invokeProv.Invoke()

End If

问候
房车

Answer 8

Answer 9

BackgroundWorker

中编写 UI 交互代码并且不会遇到跨线程操作的方法。有一天我把这个放在一起做一个项目，买家要小心！

' Init background worker
Dim _BGWorker As BackgroundWorker

' Your Windows Form's _Load event handler:
Private Sub Form_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    ' Just for this example, we're newing up the _BGWorker here
    _BGWorker = New BackgroundWorker()
    _BGWorker.WorkerReportsProgress = True
End Sub

' Magical UI Action Handling ProgressChanged Event Handler Thing (v24.4.550-alpha9) ™ ©
Private Sub _BGWorker_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs) Handles _BGWorker.ProgressChanged
    ' Take the UserState object and cast to an Action delegate type
    Dim uiAction As Action = CType(e.UserState, Action)

    ' Check if an action was passed
    If uiAction IsNot Nothing Then
        ' Run it if so!
        uiAction()
    End If
End Sub

' Standard DoWork handler for BackroundWorker
Private Sub _BGWorker_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles _BGWorker.DoWork
    '...your background worker code...

    ' EXAMPLE:
    '
    ' Me.Text = "Background worker is (trying to) change form title! :-O"
    '
    ' This line would normally fail with an exception when written directly in the DoWork
    ' handler of a BackgroundWorker. Exception you would see is:
    '   System.InvalidOperationException: Cross-thread operation not valid: Control 'FormName'
    '   accessed from a thread other than the thread it was created on.'

    ' BUT...

    ' If we write something like this:

    _BGWorker.ReportProgress(-1, New Action(
    Sub()
        '...and put that line inside this action:
        Me.Text = "Background worker is changing form title! :-O"

        ' Then NO PROBLEM! UI-interactive code MAGIC!

        ' Well, it's not magic... This works because this code is not executed here immediately.
        ' It is an Action Delegate: https://learn.microsoft.com/en-us/dotnet/api/system.action-1?view=net-7.0
        ' You can write ANY UI-interactive code inside blocks like this in your BackgroundWorkers
        ' and they will all execute on the main thread, because the Action delegate is being 
        ' shipped to the ProgressChanged event handler on the main Form thread.

        'TODO: Add your other UI code...

    End Sub))

    ' Now simply repeat the above section every time you wish write UI-interactive
    ' code in your BG workers! SHAZAM!

    '...your background worker code...
End Sub