.net - 尝试验证我的组合框时遇到问题

Question

我决定在我的组合框中添加一些验证，我想要实现的是确保用户只能输入组合框中的字段，但我现在遇到的问题是，如果用户单击组合框，不输入任何内容并尝试离开组合框，消息框出现。

Private Sub Combobox1_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles Combobox1.Validating
    If Combobox1.Items.Contains(Combobox1.Text) = False Then
        e.Cancel = True
    End If
End Sub

Private Sub Combobox1_Leave(sender As Object, e As System.EventArgs) Handles Combobox1.Leave
    If Combobox1.Items.Contains(Combobox1.Text) = False Then
        Combobox1.Select()
        MessageBox.Show("select item from combobox")
    End If
End Sub

如前所述，编码确实有效，但我试图确保如果用户未在组合框中输入任何内容，则不会出现消息框。

Answer 1

根据您的评论，我认为您需要做的就是添加一个空字符串检查:

Private Sub ComboBox1_Validating(ByVal sender As Object, ByVal e As CancelEventArgs) Handles ComboBox1.Validating
  If ComboBox1.Items.Contains(ComboBox1.Text) = False Then      
    e.Cancel = (ComboBox1.Text <> String.Empty)
  End If
End Sub

Private Sub ComboBox1_Leave(ByVal sender As Object, ByVal e As EventArgs) Handles ComboBox1.Leave
  If Not ComboBox1.Items.Contains(ComboBox1.Text) Then
    If ComboBox1.Text <> String.Empty Then
      ComboBox1.Select()
      MessageBox.Show("select item from combobox")
    End If
  End If
End Sub