substring and the indexOf function

Question

可能重复：
子串与方法的索引

我遇到了这个问题，我正在兜圈子。错误消息是"不能用这些参数调用可访问的IndexOf。">

我的教授说"要搜索字符串Los Angeles和substring会从文本框中返回它，但它需要知道从哪个位置开始返回单词，这就是IndexOf的来源。"这是否意味着substring和IndexOf一起使用？我就是这么做的，这可能就是问题所在。这是代码：

Private Sub btnOrder_Click(ByVal sender As Object, ByVal e As EventArgs)     Handles    btnOrder.Click
    'Declare variables
    Dim Price As Decimal
    Dim txtAddress As String = "Los Angeles"
    Dim DialogResults As String
    'Begin If Statements to determine whether value is a number
    If IsNumeric(txtPrice.Text) Then
        MessageBox.Show("Please enter a nummeric value.", "Error Message")
    End If
    If IsNumeric(txtQuantity.Text) Then
        MessageBox.Show("Please enter a numeric value.", "Error Message")
    End If
    Try
        'Condition for Pickup days
        If radPickUp.Checked = True Then
            Price = CDec(txtPrice.Text)
        ElseIf radNextDay.Checked = True Then
            Price = CDec(CDbl(txtPrice.Text) * 0.01)
        ElseIf radDays.Checked = True Then
            Price = CDec(CDbl(txtPrice.Text) * 0.05)
        End If
        'Condition for Weekdays or Weekends pickup
        If CDbl(Str(cboDays.Text)) = -1 Then
            Price = CDec(CDbl(txtPrice.Text) * 0.0925)
        End If
        If CBool(Int(txtAddress.Substring(0, 10))) Then
            Str(txtAddress.IndexOf(11, 0))
            DialogResults = CStr(MessageBox.Show("Your order is $ " & CDbl(txtPrice.Text) - 0.05))
        Else : DialogResults = CStr(MessageBox.Show("You order is $ " & CDbl(txtPrice.Text)))
        End If
    Catch ex As InvalidCastException
        MessageBox.Show("Please enter a valid numeric value to continue.")
    End Try    
End Sub
Private Sub btnReset_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReset.Click
    'Reset controls
    txtPrice.Clear()
    txtQuantity.Clear()
    txtName.Clear()
    txtAddress.Clear()
    cboDays.Text = String.Empty
    txtPrice.Focus()
End Sub
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
    'Quit the application
    Me.Close()
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    MessageBox.Show("Hello", "A greeting.")
End Sub

有什么建议吗？

Answer 1

文档是的朋友

你打电话给

Str(txtAddress.IndexOf(11, 0))

这是无效语法。正确的语法是

string.IndexOf(searchString)

这将返回找到的字符串的索引位置

-如果未找到，则为1。

如果为空，则为0