如何以編程方式從ReadOnly RichTextBox中刪除文本？

Question

下面的代碼旨在保留一個文本緩衝區在一個ReadOnly RichTextBox中，最大數量的字符存儲，並始終保持滾動到底部。它傳輸實時日誌。

但在我試圖保持最大字符數，rtMessages.TextLength()rtMessages.SelectedText = String.Empty因此之後沒有改變，沒有防守If塊，我結束了一個無限循環試圖多次刪除緩衝區的第一行。

當我刪除RichTextBox的ReadOnly時，此功能成功。似乎有點奇怪，因爲AppendText成功，但我明白，選擇是一個不同的野獸。

我可以讓這個一個ReadOnlyRichTextBox是編程修改？

Private Sub onNewData(ByRef data As String) Handles _server.clientSentData 

    ' Add new text 
    rtMessages.SelectionStart = rtMessages.TextLength() 
    rtMessages.AppendText(data) 

    ' Delete oldest text line-by-line until the whole buffer is shorter than MAX_TEXT_LENGTH characters 
    Const MAX_TEXT_LENGTH = 200 
    Dim textLength = rtMessages.TextLength() 
    While textLength > MAX_TEXT_LENGTH 
     Dim i As Int16 = 0 
     Do While rtMessages.GetLineFromCharIndex(i) < 1 
      i += 1 
     Loop 

     rtMessages.Select() 
     rtMessages.SelectionStart = 0 
     rtMessages.SelectionLength = i 
     rtMessages.SelectedText = String.Empty 
     rtMessages.SelectionLength = 0 

     If rtMessages.TextLength() = textLength Then 
      rtMessages.Clear() 
      rtMessages.AppendText("[buffer trimming algorithm failed]") 
      Exit While 
     End If 

     textLength = rtMessages.TextLength() 
    End While 

    ' Scroll down 
    rtMessages.SelectionStart = rtMessages.TextLength() 
    rtMessages.ScrollToCaret() 
End Sub 

Answer 1

雖然試圖取代SelectedText在一個只讀的RichTextBox不工作，使用SelectedRtf做工作：

'rtMessages.Select() 
    'rtMessages.SelectionStart = 0 
    'rtMessages.SelectionLength = i 
    'rtMessages.SelectedText = String.Empty 
    'rtMessages.SelectionLength = 0 

    rtMessages.Select(0, i) 
    rtMessages.SelectedRtf = "{\rtf1\ansi}" 

Answer 2

rtMessages.SelectionLength = i - 1 

應該

rtMessages.SelectionLength = i 

編輯＃1

代替通過添加-1到SelectionLength，你錯過了第一行的最後一個字符。第二次運行時，第一行中只有1個字符（第一次運行時錯過的那個字符）。然後，您將嘗試刪除SelectionLength爲0，並且您將爲其他所有運行獲得相同的TextLength，然後您將使用無限循環！

Answer 3

您可以刪除只讀參數，編寫附加的文本代碼，然後再次將richtextbox設置爲只讀。

Answer 4

我知道這是一個古老的線程，但你可以避開ReadOnly問題替換下面的代碼：

rtMessages.Select() 
rtMessages.SelectionStart = 0 
rtMessages.SelectionLength = i 
rtMessages.SelectedText = String.Empty 
rtMessages.SelectionLength = 0 

與此：

rtMessages.Text = rtMessages.Text.Substring(i) 

我不知道，如果這性能會好轉還是差一些，但是它會在RichTextBox左右被設置爲ReadOnly

編輯：

這裏是用來測試這個完整的代碼（注：我添加的代碼到Button.Click用於測試）

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 
    Static X As Integer = 0 
    X += 1 

    Dim Data As String = "Line " & X.ToString & ControlChars.NewLine 
    Me.onNewData(Data) 
End Sub 

Private Sub onNewData(ByRef data As String) 

    ' Add new text 
    rtMessages.SelectionStart = rtMessages.TextLength() 
    rtMessages.AppendText(data) 

    ' Delete oldest text line-by-line until the whole buffer is shorter than MAX_TEXT_LENGTH characters 
    Const MAX_TEXT_LENGTH As Integer = 200 
    Dim textLength As Integer = rtMessages.TextLength() 
    While textLength > MAX_TEXT_LENGTH 
     Dim i As Integer = 0 
     Do While rtMessages.GetLineFromCharIndex(i) < 1 
      i += 1 
     Loop 

     'rtMessages.Select() 
     'rtMessages.SelectionStart = 0 
     'rtMessages.SelectionLength = i 
     'rtMessages.SelectedText = String.Empty 
     'rtMessages.SelectionLength = 0 

     rtMessages.Text = rtMessages.Text.Substring(i) 

     If rtMessages.TextLength() = textLength Then 
      rtMessages.Clear() 
      rtMessages.AppendText("[buffer trimming algorithm failed]") 
      Exit While 
     End If 

     textLength = rtMessages.TextLength() 
    End While 

    ' Scroll down 
    rtMessages.SelectionStart = rtMessages.TextLength() 
    rtMessages.ScrollToCaret() 

End Sub