Vb.net 避免文本框中的现有项

我编写了一个代码，用于将项目从ListBox移动到RichTextBox

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如何验证列表项是否已存在

我找到了问题的答案

我使用[.contains（）]函数验证文本是否已存在

  Private Sub BtnMoveItemstoTemplate_Click(sender As Object, e As EventArgs) Handles BtnMoveItemstoTemplate.Click
    Try
        If LBMessageContents.SelectedItem Is Nothing Then
            ShowMessage("Select Some Details to Send a Message")
        Else
           RTMsgContent.Text = RTMsgContent.Text & LBMessageContents.SelectedItem
        End If

    Catch ex As Exception
        HandleClassException(ex)
    End Try
End Sub

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正如vinayak所说，您可以使用

.contains（）

来了解文本框是否包含字符串

   Private Sub BtnMoveItemstoTemplate_Click(sender As Object, e As EventArgs) Handles BtnMoveItemstoTemplate.Click
    Try
    If LBMessageContents.SelectedItem Is Nothing Then
        ShowMessage("Select Some Details to Send a Message")
    Else

   **If RtMsgContent.Text.Contains(LBMessageContents.SelectedItem) then Exit Sub**

       RTMsgContent.Text = RTMsgContent.Text & LBMessageContents.SelectedItem
    End If

  Catch ex As Exception
    HandleClassException(ex)
  End Try
  End Sub

Private Sub BtnMoveItemstoTemplate_Click(sender As Object, e As EventArgs) Handles BtnMoveItemstoTemplate.Click
  Try
    If LBMessageContents.SelectedItem Is Nothing Then
        ShowMessage("Select Some Details to Send a Message")
    Else
        'check if the item already exists
        If RtMsgContent.Text.Contains(LBMessageContents.SelectedItem) then
            'do what you want to do if the item already exists. like showing message
            MsgBox("Error! This item already exists")
        Else
            'doesn't already exists, add to the textbox
            RTMsgContent.Text = RTMsgContent.Text & LBMessageContents.SelectedItem
        End If
    End If
Catch ex As Exception
    HandleClassException(ex)
  End Try
End Sub