Question

我正在尝试显示“找不到记录”消息框，但我不知道如何编写代码。这是我的代码：

Public Class Form1
    Dim cnn As New OleDb.OleDbConnection

    Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
        Dim cmd As New OleDb.OleDbCommand
        If Not cnn.State = ConnectionState.Open Then
            cnn.Open()
        End If

        cmd.Connection = cnn

        If Me.TextBox1.Text <> "" Then
            cmd.CommandText = "INSERT INTO Student(StudentName, StudentID) " & _
                " VALUES('" & Me.TextBox1.Text & "','" & Me.TextBox2.Text & "')"
                cmd.ExecuteNonQuery()

            MsgBox("Record added")
        Else
            MsgBox("Please fill in required fields")
        End If

        cnn.Close()
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
        cnn = New OleDb.OleDbConnection
        cnn.ConnectionString = "Provider=Microsoft.Jet.Oledb.4.0; Data Source=" & Application.StartupPath & "\Testing.mdb"

    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If Not cnn.State = ConnectionState.Open Then
            cnn.Open()
        End If

        Dim da As New OleDb.OleDbDataAdapter("SELECT * FROM Student WHERE StudentName='" & Me.TextBox1.Text & "'", cnn)

        Dim dt As New DataTable
        da.Fill(dt)

        Me.TextBox3.Text = dt.Rows(0).Item("StudentName")
        Me.TextBox4.Text = dt.Rows(0).Item("StudentID")

        cnn.Close()

    End Sub
End Class

请告知如何编写If Else代码，以便在没有记录的情况下，将显示“未找到记录”消息。感谢。

Answer 1

如果我理解了您的问题，您需要先检查数据集中是否有数据，然后再显示在文本框中（Button1_Click事件中的代码）。你可以试试这个;

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If Not cnn.State = ConnectionState.Open Then
        cnn.Open()
    End If

    Dim da As New OleDb.OleDbDataAdapter("SELECT * FROM Student WHERE StudentName='" & Me.TextBox1.Text & "'", cnn)

    Dim dt As New DataTable
    da.Fill(dt)

    // Assuming that at this stage, dt already contains the data
    If dt.Rows.Count > 0 then
       Me.TextBox3.Text = dt.Rows(0).Item("StudentName")
       Me.TextBox4.Text = dt.Rows(0).Item("StudentID")
    Else
       MsgBox("No records found")
    EndIf

    cnn.Close()

End Sub

Visual Basic - 如果没有找到记录，如何显示消息？

1 个答案: