Question

如果在比较结束时没有从数据库中提取数据，我正在尝试显示一个消息框

Private Sub submitbutton_Click(sender As Object,
e As EventArgs) Handles submitbutton.Click myConnection.Open()
 tutorboxr.Clear()
 compboxr.Clear()
 Dim str As String
 Dim etr As String
 str="SELECT * FROM 2014Results WHERE (Competitor = '" & Competitor.Text &"')"
 etr="SELECT * FROM 2014Results WHERE (Event = '" & EventBox.Text &"')"
 
Dim cmd As OleDbCommand=New OleDbCommand(str,
myConnection) 

Dim emd As OleDbCommand=New OleDbCommand(etr,
myConnection) dr=cmd.ExecuteReader

While dr.Read() 
compboxr.Text=dr("Rank").ToString 
textbox.Text=dr("Reg").ToString

If Competitor.Text="" Then MessageBox.Show("This student wasn't a ranking placeholder!",
MessageBoxButtons.OK,
MessageBoxIcon.Error) 
End If 
End While myConnection.Close() 

If Competitor.Text="" Then MessageBox.Show("Please enter a students name",
"No entry",
MessageBoxButtons.OK,
MessageBoxIcon.Error) With Competitor .Focus() .SelectAll() End With Exit Sub 
End If
End Sub

我收到此错误：

重载分辨率失败，因为在没有缩小转换的情况下无法调用可访问的“Show”::参数匹配参数从“MessageBoxButtons”缩小为“String”。：参数匹配参数从'MessageBoxButtons'缩小。：参数匹配参数从'String'缩小到。：参数匹配参数'text'从'MessageBoxButtons'缩小为'String'。：参数匹配参数从'String'缩小。

Answer 1

看起来您在第一次MessageBox.Show来电时缺少参数：

If Competitor.Text="" Then
    MessageBox.Show("This student wasn't a ranking placeholder!",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error) 
End If

应该像第二个电话：

If Competitor.Text="" Then
    MessageBox.Show("This student wasn't a ranking placeholder!",
                    "** a caption here **",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error) 
End If

如果搜索后文本框为空，如何显示消息框

1 个答案: