Question

我有一个分配，用户将在列表框中输入数字。当用户输入数字时，它将计算平均值和标准偏差。（我们的教授不希望我们使用内置的标准差函数）程序将有一个上下文菜单，这些是创建菜单的指南：您必须创建一个名为SetMenu的子例程。它用于根据列表的内容启用和禁用上下文菜单。当列表为空时，禁用清除。当列表中至少包含一个数字时，将启用“清除”。如果未选择任何内容，则禁用“删除项目”。选择某些内容后，将启用“删除项目”。这就是我需要帮助的地方，创建了这个子程序。

这是我的代码：

Option Strict On
Public Class Form1

Private Sub AddBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AddBtn.Click
    ListBox.Items.Add(InputBox.Text)
    InputBox.Text = ""
End Sub

Private Sub ComputeBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComputeBtn.Click
    Dim sum, x, number, numberSum, subtractedNum As Integer
    Dim average, insideRoot, squaredRoot As Double


    For x = 0 To ListBox.Items.Count - 1
        ListBox.SelectedIndex = x

        number = Integer.Parse(ListBox.SelectedItem.ToString)
        sum = sum + number
        average = sum / ListBox.Items.Count
    Next
    AverageLbl.Text = average.ToString

    For x = 0 To ListBox.Items.Count - 1
        ListBox.SelectedIndex = x
        number = Integer.Parse(ListBox.SelectedItem.ToString)

        subtractedNum = CInt((number - average) ^ 2)
        numberSum = numberSum + subtractedNum
        insideRoot = (numberSum / (ListBox.Items.Count - 1))
        squaredRoot = insideRoot ^ (1 / 2)
    Next
    DeviationLbl.Text = squaredRoot.ToString("N2")

End Sub

Private Sub ClearMenu_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ClearMenu.Click
    ClearMenu.Enabled = False
    SetMenu()
    ListBox.Items.Clear()
End Sub

Private Sub DeleteMenu_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DeleteMenu.Click
    ListBox.Items.Remove(ListBox.SelectedItem)
End Sub

Private Sub InputBox_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles InputBox.TextChanged
    If IsNumeric(InputBox.Text) And InputBox.Text <> "" Then
        AddBtn.Enabled = True
    Else
        AddBtn.Enabled = False
    End If
End Sub

Private Sub SetMenu()
    'Need help here
End Sub

结束班

Answer 1

怎么样：

Private Sub toggleContextMenuItems()

    ClearToolStripMenuItem.Visible = (ListBox1.Items.Count > 0)

    DeleteToolStripMenuItem.Visible = (ListBox1.SelectedIndex > -1)

End Sub

然后在需要时调用此方法。

Visual Basic中的ListBoxes

1 个答案: