mysql - 如果 mysql 查询为空，则程序崩溃

Question

我有这个表格，显示未完成的传输操作，以便经理可以完成它们，它只显示正在进行的操作，如果没有正在进行的操作，程序就会崩溃，我试图通过放置一个 MsgBox 来避免这种情况，但是它不起作用。我怎样才能使这个 msgbox 解决方案发挥作用？

Private Sub editarops_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Timer1.Enabled = True
    conexao.ConnectionString = "server = localhost; user =root; database = frota;"
    conexao.Open()
    comando.Connection = conexao
    strsql = "SELECT codtrab, carga, origem, destino, estado, dataini FROM trabalhos where estado = 'En Route'"
    comando.Connection = conexao
    strsql = "SELECT codtrab, carga, origem, destino, estado, dataini FROM trabalhos where estado = 'En Route'"
    comando.CommandText = strsql
    r3 = comando.ExecuteReader
    If bs.Count = 0 Then

        bs.DataSource = r3


        ComboBox1.Text = bs.Current(0)
        tboxfunc.Text = bs.Current(1)
        TextBox1.Text = bs.Current(2)
        TextBox2.Text = bs.Current(3)
        TextBox3.Text = bs.Current(5)
        Atualizar.Enabled = True
        Cancelar.Enabled = True
        r3.Close()

        Dim sStmt1 As String = "Select codtrab from trabalhos where estado = 'En Route' "
        Dim cmd1 As New MySqlCommand(sStmt1, conexao)
        Dim da1 As MySqlDataAdapter = New MySqlDataAdapter(cmd1)
        Dim dt1 As New DataTable("trabalhos")
        da1.Fill(dt1)
        If dt1.Rows.Count > 0 Then
            ComboBox1.DataSource = dt1
            ComboBox1.DisplayMember = "codtrab"
        Else
            MsgBox("Não existem Funcionários", vbExclamation)
            Me.Close()
            Inicio.Show()
        End If
        da1.Dispose()
        repor()
        TextBox1.Enabled = False
        TextBox2.Enabled = False
        TextBox3.Enabled = False
        TextBox4.Enabled = False
        TextBox5.Enabled = False
        TextBox6.Enabled = False
        tboxfunc.Enabled = False
        btcancelar.Visible = False

    Else
        MsgBox("Não existem Operações En Route", vbExclamation)
        Me.Close()
        Inicio.Show()
    End If
End Sub

Answer 1

1. 您应该将连接字符串放在Using block 中，或者手动处理它。不过，这通常不会导致崩溃。
2. 如果 Inicio 是“调用”表单，您可以关闭此表单而不显示 Inicio。
3. 尝试在 Me.Close 之后添加“Exit Sub”。