Mysql VB.NET函数返回错误并退出子对象

我在VB.NET项目中有这个连接函数

Public Function OpenMysqlCon() As MySqlConnection
    Dim mMysqlconnection = New MySqlConnection()
    Try
        Dim strconDB As String = "server='192.168.100.2'; database='mydb';Port=3306; UID='epb'; password='hahaha'; pooling=true"
        mMysqlconnection = New MySqlConnection
        mMysqlconnection.ConnectionString = strconDB
        mMysqlconnection.Open()
        OpenMysqlCon = mMysqlconnection
    Catch exceptionThatICaught As System.Exception
        OpenMysqlCon = Nothing
    End Try
End Function

我将在我的VB项目中调用函数

Private Sub frmTest_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Using Con=OpenMysqlCon()
        'mycode here
    End Using
End Sub

但是，当连接不可用时，它将引发异常

我如何通过给msgbox提供像

连接这样的连接来避免异常，此时不可用，请稍后重试

，然后退出正在使用该功能的子系统

---

End Sub

它将是这样的

Public Function OpenMysqlCon() As MySqlConnection
    Dim mMysqlconnection As MySqlConnection()
    Try
        Dim strconDB As String = "server='192.168.100.2'; database='mydb';Port=3306; UID='epb'; password='hahaha'; pooling=true"
        mMysqlconnection = New MySqlConnection
        mMysqlconnection.ConnectionString = strconDB
        mMysqlconnection.Open()
    Catch exceptionThatICaught As System.Exception
        mMysqlconnection = Nothing
    End Try
    Return mMysqlconnection
End Function

Private Sub frmTest_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim con As MySqlConnection = OpenMysqlCon
    If con Is Nothing Then
        MessageBox.Show("connection not available at the moment, please try again later")
        'Me.Close 'uncomment if the app should end
    End If
End Sub

编辑-未对其进行测试

    Using con As MySqlConnection = OpenMysqlCon
        If con Is Nothing Then
            MessageBox.Show("connection not available at the moment, please try again later")
            'Me.Close 'uncomment if the app should end
        Else
            'your code
        End If
    End Using

---

最好的方法不是将连接保存在表单的字段中，而是在需要的地方创建并初始化它。连接池将确保不需要创建物理连接

因此，不要使用

OpenMysqlCon

方法，而是使用这样的代码（

GetAllUsers

只是一个示例）：

---

可能有帮助，因为相关（您也在重复使用连接）：

这是OpenMysqlCon，我已经更正了输入错误，抱歉，朋友。我正在尝试使用

使用
语句，所以我不必费心在代码结束时关闭连接。当
不返回任何内容时，
它仍然是一样的，因为我还是会有例外。@JosephGoh:那你想要什么就给我什么。这不是重点。关键是，您不应该将连接保持在使用它的方法之外。当然，无论在哪里调用该方法，都必须处理该方法返回
Nothing
的情况。
Public Function GetAllUsers() As List(Of User)
    Dim userList = New List(Of User)

    Try
        Using mMysqlconnection = New MySqlConnection("server='192.168.100.2'; database='mydb';Port=3306; UID='epb'; password='hahaha'; pooling=true")
            mMysqlconnection.Open()
            Using command = New MySqlCommand("SELECT * FROM USER ORDER By UserName", mMysqlconnection)
                Using rdr = command.ExecuteReader()
                    While rdr.Read()
                        Dim user = New User()
                        user.UserName = rdr.GetString(0)
                        userList.Add(user)
                    End While
                End Using
            End Using
        End Using
    Catch exceptionThatICaught As System.Exception
        MessageBox.Show("meaningful message here, logging would be useful too")
        Return Nothing
    End Try

    Return userList
End Function