VB.net空错误
我在尝试处理ArgumentNullExection时遇到问题 值不能为空 参数名称项 到目前为止,我尝试了以下方法VB.net空错误,vb.net,null,argumentnullexception,Vb.net,Null,Argumentnullexception,我在尝试处理ArgumentNullExection时遇到问题 值不能为空 参数名称项 到目前为止,我尝试了以下方法 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim ArgumentNullException As New Boolean If (ListBox2.Items.Add(Lis
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim ArgumentNullException As New Boolean
If (ListBox2.Items.Add(ListBox1.SelectedItem.ToString = "")) Then
MessageBox.Show("please pick from list", "error")
End If
ListBox1.Items.Remove(ListBox1.SelectedItem)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim ArgumentNullException As New Boolean
If (ListBox2.Items.Add(ListBox1.SelectedItem Is Nothing)) Then
MessageBox.Show("please pick from list", "error")
End If
ListBox1.Items.Remove(ListBox1.SelectedItem)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim ArgumentNullException As New BooleanListBox2
ListBox2.Items.Add(ListBox1.SelectedItem)
If (ListBox1.SelectedItem) = ""
MessageBox.Show("please pick from list", "error")
ListBox1.Items.Remove(ListBox1.SelectedItem)
还有错误,有人能帮忙吗
更新:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
ListBox2.Items.Add(ListBox1.SelectedItem)
If IsNothing (ListBox1.SelectedItem)
MessageBox.Show("please pick from list", "error")
ListBox1.Items.Remove(ListBox1.SelectedItem)
给出错误仍然问题很不清楚,但我会尝试一下
当您的应用程序具有
列表框
并使用.SelectedItem
属性时,您应该始终使用Try/Catch,甚至更好地检查用户是否选择了以下项:
If IsNothing(ListBox1.SelectedItem) Then Exit Sub
你也可以使用
If ListBox1.SelectedItems.Count = 0 Then Exit Sub
您也可以使用If/Else,但在我看来,将语句放在代码的第一行可以使它更具可读性
当没有选定的项目时,使用此代码将使按钮不执行任何操作。
否则,您可以使用多行If来放置MsgBox(“请选择项目”)
,以警告用户:
If IsNothing(ListBox1.SelectedItem) Then
MsgBox("Please pick an Item first.")
Exit Sub
End If
// Your Code after that
您最好粘贴整个相关代码,例如列表变量的初始化。这到底是什么:
If(ListBox2.Items.Add(ListBox1.SelectedItem.ToString=”“)然后
?Noob试用和错误我读了一篇不起作用的帖子,然后就尝试了不同的组合。我的目标是,如果用户只是按下按钮而没有选择项目,消息框就会出现感谢错过了结尾子项很高兴我能帮上忙。始终记住:打开的所有内容都需要在某个位置关闭:If/End If、While/EndWhile、Function/End Function、Sub/End Sub、Select Case/End Select、(…)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
// Leave the Sub and Message the User, when there is no SelectedItem
If IsNothing(ListBox1.SelectedItem) Then
MsgBox("Please pick an Item first.")
Exit Sub
End If
// Code will only reach here, when there is a SelectedItem
ListBox2.Items.Add(ListBox1.SelectedItem)
ListBox1.Items.Remove(ListBox1.SelectedItem)
End sub