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Question

Form1.vb

Imports System.Threading

Public Class Form1

Dim demoThread As Thread

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    Dim Start As New Class1
    Me.demoThread = New Thread( _
            New ThreadStart(AddressOf Start.ThreadProcSafe))

    Me.demoThread.Start()

End Sub
Delegate Sub SetTextCallback([text] As String)
Public 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
End Class

Class1.vb

Public Class Class1

Public Sub ThreadProcSafe()
    Form1.SetText("This text was set safely.")
End Sub
End Class

谁能告诉我为什么这不更新文本框？

当 ThreadProcSafe 在 Form1 内部被调用（并且仍然由线程启动）但当它从类外移到另一个类时，它可以工作，没有警告或错误但不会更新。

Answer 1

原因是您在第二个代码 sn-p 中引用了默认实例。默认实例是线程特定的，因此第二个代码 sn-p 将创建一个 Form1 类型的新实例，而不是使用现有实例。您的 Class1 需要引用 Form1 的原始实例。

如果这不切实际，那么解决方案是不在表单中进行委托，而是在访问表单的类中使用SynchronizationContext 类进行。