删除多行文本框中的单行代码答案

【问题标题】：Remove single line of code in multi-line textbox删除多行文本框中的单行代码
【发布时间】：2018-03-21 09:14:43
【问题描述】：

我正在尝试编写一个按钮，单击该按钮会删除多行文本框中的最后一行文本。如果文本框中有两行文本，它可以删除最后一行文本，但如果文本框中只有一行，则会导致错误。

例如。将此添加到框中：

line of text 1
line of text 2

使用删除按钮两次，我可以删除两行文本

但如果我这样做：将此行添加到文本框：

line of text 1

然后尝试删除它，它会出错。

我知道这是错误的，因为我使用了两次

            ' remove box text
        QuoteHistoryBox.Text = QuoteHistoryBox.Text.Remove(QuoteHistoryBox.Text.LastIndexOf(Environment.NewLine))
        QuoteHistoryBox.Text = QuoteHistoryBox.Text.Remove(QuoteHistoryBox.Text.LastIndexOf(Environment.NewLine))

但是由于程序的工作原理，这段代码是必须保留的，并且想知道是否有解决方法。

这是删除最后一个按钮的代码：

    Private Sub Button12_Click(sender As Object, e As EventArgs) Handles RemoveLastBtn.Click
    ' do absolutelty nothing if the box is already empty
    If QuoteHistoryBox.Lines.Count = 1 Or QuoteHistoryBox.Text = "" Then
        QuoteHistoryBox.Text = ""
        FinalQuoteBox.Text = 0
        removeOne = 0
        ' else, remove the last line of text, which would be the last item
    ElseIf removeOne = 0 Then
        ' create a place to store the last line in the texbox
        Dim lastBoxLine As String

        'get the last line in the textbox
        lastBoxLine = QuoteHistoryBox.Lines(QuoteHistoryBox.Lines.Length - 1)

        'if the last line is empt, get the second line instead
        If (lastBoxLine = String.Empty Or lastBoxLine = "") Then
            lastBoxLine = QuoteHistoryBox.Lines(QuoteHistoryBox.Lines.Length - 2)
        End If

        ' compare the gotten line with the number of strings
        ' if the last line matches this string, delete it, and then minus the number associated with this string, or plus if it is the contract string
        If lastBoxLine.Equals("+ Base 3D Printer: $799") Then
            lastNum = 799
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ High-end Printer: $3999") Then
            lastNum = 3999
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic small print: $30") Then
            lastNum = 30
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic medium print: $50") Then
            lastNum = 50
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic large print: $110") Then
            lastNum = 110
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ High quality fdm print: %110") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 210
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ Fdm print using ABS: %20") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 120
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ High quality SLA print: %210") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 310
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ Contract: - %15") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 85
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ Prioritise request: $20") Then
            lastNum = 20
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        End If

        ' remove box text
        QuoteHistoryBox.Text = QuoteHistoryBox.Text.Remove(QuoteHistoryBox.Text.LastIndexOf(Environment.NewLine))
        QuoteHistoryBox.Text = QuoteHistoryBox.Text.Remove(QuoteHistoryBox.Text.LastIndexOf(Environment.NewLine))
        removeOne = removeOne + 1

    Else

        ' create a place to store the last line in the texbox
        Dim lastBoxLine As String

        'get the last line in the textbox
        lastBoxLine = QuoteHistoryBox.Lines(QuoteHistoryBox.Lines.Length - 1)

        'if the last line is empt, get the second line instead
        If (lastBoxLine = String.Empty Or lastBoxLine = "") Then
            lastBoxLine = QuoteHistoryBox.Lines(QuoteHistoryBox.Lines.Length - 2)
        End If

        ' compare the gotten line with the number of strings
        ' if the last line matches this string, delete it, and then minus the number associated with this string, or plus if it is the contract string

        If lastBoxLine.Equals("+ Base 3D Printer: $799") Then
            lastNum = 799
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ High-end Printer: $3999") Then
            lastNum = 3999
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic small print: $30") Then
            lastNum = 30
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic medium print: $50") Then
            lastNum = 50
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ Basic large print: $110") Then
            lastNum = 110
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        ElseIf lastBoxLine.Equals("+ High quality fdm print: %110") Then
            ' correctly gets the old money value before the increase
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 210
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ Fdm print using ABS: %20") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 120
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ High quality SLA print: %210") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 310
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
        ElseIf lastBoxLine.Equals("+ Contract: - %15") Then
            Dim currentVal As Double = Val(FinalQuoteBox.Text)
            lastNum = currentVal / 85
            lastNum = lastNum * 100
            FinalQuoteBox.Text = lastNum
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) + lastNum
        ElseIf lastBoxLine.Equals("+ Prioritise request: $20") Then
            lastNum = 20
            FinalQuoteBox.Text = Val(FinalQuoteBox.Text) - lastNum
        End If

        QuoteHistoryBox.Text = QuoteHistoryBox.Text.Remove(QuoteHistoryBox.Text.LastIndexOf(Environment.NewLine))
        removeOne = removeOne + 1

    End If

End Sub

不胜感激。

【问题讨论】：

标签： vb.net

【解决方案1】：

没关系，我找到了答案。我只是把它放在一个 try catch 块中并添加：

Catch ex As ArgumentOutOfRangeException
        QuoteHistoryBox.Text = ""
        FinalQuoteBox.Text = 0
        removeOne = 0
    End Try

当行只有一个项目时捕获，如果它在捕获块中，则执行特定的操作。问题解决了。

【讨论】：