如何将文本从VB.NET Winform中的另一个类追加到richTextBox？

Question

I've got a winform named Form1.vb and a class named FZConsole.vb On the winform I've got a Richtextbox1 and I'm trying to append text to it from the class but it won't work.

From the Form1.vb I can easily do

Richtextbox1.AppendText("Console is currently ON.")

In the class I'm trying to do this, but it won't work:

Class FZConsole
Public Sub FZConsole()
    While True
            Form1.Richtextbox1.AppendText(Environment.NewLine & "Test From Class")

        Threading.Thread.Sleep(1)
    End While
End Sub
End Class

Answer 1

When accessing controls from another thread you must typically invoke the accessing/updating of the control. This is done to synchronize the updating of the controls, so that two threads does not update one control at the same time.

You can think of it like this: two people cannot write at the same paper at the same time.

Invocation is usually nothing hard. It's basically just doing these two things:

1. Check if invocation is required by the control or it's container.
2. Invoke if necessary.

Invocation is performed using Delegate methods. If you target .NET Framework 4.0 or higher you can use the Sub() lambda expression to create a very simple delegate.

Public Sub FZConsole()
    While True
        If Form1.InvokeRequired = True Then 'Invocation is required.'
            Form1.Invoke(Sub() Form1.Richtextbox1.AppendText(Environment.NewLine & "Test From Class"))
        Else 'Invocation is not required.'
            Form1.Richtextbox1.AppendText(Environment.NewLine & "Test From Class")
        End If

        Threading.Thread.Sleep(1)
    End While
End Sub

---

However if you target .NET Framework 3.5 or lower things become a little trickier. When targeting an earlier framework you have to declare the delegate yourself, and it's not as simple as using the lambda since it works differently when passing variables.

Delegate Sub TextUpdaterDelegate(ByVal Text As String)

Public Sub FZConsole()
    While True
        If Form1.InvokeRequired = True Then 'Invocation is required.'
            Form1.Invoke(New TextUpdaterDelegate(AddressOf RichTextBox1.AppendText), Environment.NewLine & "Test From Class")
        Else 'Invocation is not required.'
            Form1.Richtextbox1.AppendText(Environment.NewLine & "Test From Class")
        End If

        Threading.Thread.Sleep(1)
    End While
End Sub

Answer 2

Public Class Form1

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim newInstanceToClass As New SomeClass
        RichTextBox1.AppendText(newInstanceToClass.returenText)
    End Sub


    Class SomeClass
        Function returenText() As String
            Dim txt As String = "some text..."
            Return txt
        End Function
    End Class
End Class