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我的 VB.NET 项目中有这个连接功能

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 项目中调用该函数，例如

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，它会抛出异常。

我怎样才能通过给一个 msgbox 类似的东西connection not available at the moment, please try again later然后退出正在使用该函数的子程序来避免异常？

结束子

4

2 回答 2

0

它会是这样的。

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 - 这未经测试

    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
于 2017-04-07T09:18:40.373 回答
0

最好的方法是不在表单的字段中保持连接，而是在需要的地方创建和初始化它。连接池将确保不需要创建物理连接。

所以不要使用任何OpenMysqlCon方法，而是这样的代码（GetAllUsers只是一个例子）：

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

可能有帮助，因为相关（您也在重用连接）：ExecuteReader 需要一个开放且可用的连接。连接的当前状态是 Connecting

于 2017-04-07T09:29:47.003 回答