VB.NET - MessageBox YesNo 条件语句不起作用 [英] VB.NET - MessageBox YesNo Conditional Statement not working

问题描述

我有一个程序，用于清除用户用来回答多项选择题的组合框.如果用户单击清除，则会弹出一个消息框并询问用户是否确定要清除表单.如果他们按是，它会清除所有组合框.截至目前，如果用户按否"，它仍会清除组合框.

I have a program where I am clearing out comboboxes that the user is using to answer multiple choice questions. If the user clicks Clear, a messagebox pops up and asks the user if they are sure they want to clear out the form. If they press yes, it clears out all comboboxes. As of right now, if the user presses no, it still clears out the comboboxes.

代码:

  Private Sub btnClear_Click(sender As Object, e As EventArgs) Handles btnClear.Click

    MessageBox.Show("Are you sure you want to clear your answers?", "Attention!",             MessageBoxButtons.YesNo)
    If Windows.Forms.DialogResult.Yes Then
        For Each cbo As ComboBox In Controls.OfType(Of ComboBox)()
            cbo.Items.Clear()
        Next
    End If


End Sub

推荐答案

您需要捕获 MessageBox 结果:

You need to capture the MessageBox result:

Dim dlgR as DialogResult

DlgR = MessageBox.Show("Are you sure you want to clear your answers?", 
            "Attention!", MessageBoxButtons.YesNo)

' then test it:
If dlgR = DialogResult.Yes Then
    For Each cbo As ComboBox In Controls.OfType(Of ComboBox)()
        cbo.Items.Clear()
    Next
End If

MessageBox 是一个返回 DialogResult 的函数.你的代码

MessageBox is a function which returns a DialogResult. Your code

If Windows.Forms.DialogResult.Yes Then...

不评估用户的响应；DialogResult.Yes 不是 False (0)，因此它将始终为 True 并导致 CBO 无论他们回答什么都会被清除.

isnt evaluating the user's response; DialogResult.Yes is not False (0), so it will always be True and cause the CBOs to be cleared no matter what they answer.

此外，该代码在 Option Strict 下是不合法的.如果 Option Strict 开启，VB/VS 会通知你并提示你改变它；这将避免在其他地方出现许多类似且更严重的错误.

Also, that code is not legal under Option Strict. VB/VS would inform you of this and prompt you to change it if Option Strict is on; this will avoid many similar - and more serious - errors elsewhere.

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