Question

在这个程序（VB，ASP.NET 2010）中，我创建了三个字段：accno，name和balance，以及以下按钮：create，{{ 1}}，destroy和set。但是，在点击get或set方法时，它会出现以下异常：get

Default.aspx.vb

object reference not set to an instance of an object

Account.vb

Partial Class _Default
    Inherits System.Web.UI.Page

    Dim obj As account 'declaring the obj of class account

    Protected Sub btn_create_Click(sender As Object, e As System.EventArgs) Handles btn_create.Click
        obj = New account 'initializing the object obj on class accounts
    End Sub    

    Protected Sub btn_set_Click(sender As Object, e As System.EventArgs) Handles btn_set.Click
        'sending the values from textboxes to accounts class through method setdata
        Try
            obj.setdata(CInt(txt_accno.Text), (txt_name.Text), CInt(txt_bal.Text))
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Protected Sub btn_get_Click(sender As Object, e As System.EventArgs) Handles btn_get.Click
        'calling the method getdata to view the output
        Try
            obj.getdata()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Protected Sub btn_destroy_Click(sender As Object, e As System.EventArgs) Handles btn_destroy.Click
        'calling the constructor
        obj = Nothing
    End Sub
End Class

Answer 1

您已使用新关键字初始化对象...

Dim obj作为新帐户

Default.aspx.vb Partial Class _Default Inherits System.Web.UI.Page

'declaring the obj of class account

Dim obj As NEW account    


Protected Sub btn_create_Click(sender As Object, e As System.EventArgs) Handles btn_create.Click

    'initializing the object obj on class accounts
    obj = New account



End Sub


Protected Sub btn_set_Click(sender As Object, e As System.EventArgs) Handles btn_set.Click

    'sending the values from textboxes to accounts class through method setdata

    Try
        obj.setdata(CInt(txt_accno.Text), (txt_name.Text), CInt(txt_bal.Text))

    Catch ex As Exception

        MsgBox(ex.Message)
    End Try


End Sub

Protected Sub btn_get_Click(sender As Object, e As System.EventArgs) Handles btn_get.Click

    'calling the method getdata to view the output

    Try

        obj.getdata()

    Catch ex As Exception

        MsgBox(ex.Message)
    End Try

End Sub

Protected Sub btn_destroy_Click(sender As Object, e As System.EventArgs) Handles btn_destroy.Click

    'calling the constructor

    obj = Nothing

End Sub
End Class

如果有效，请将其标记为答案。

Answer 2

使用下面的代码。你需要初始化页面加载方法，需要检查是回发属性。

 Default.aspx.vb Partial Class _Default Inherits System.Web.UI.Page

        'declaring the obj of class account

        Dim obj As account 

        Sub Page_Load(ByVal Sender As System.Object, ByVal e As System.EventArgs)
            if not ispostback then
                 obj = New account
            end
       End Sub

        Protected Sub btn_create_Click(sender As Object, e As System.EventArgs) Handles btn_create.Click

            'initializing the object obj on class accounts
            obj = New account



        End Sub


        Protected Sub btn_set_Click(sender As Object, e As System.EventArgs) Handles btn_set.Click

            'sending the values from textboxes to accounts class through method setdata

            Try
                obj.setdata(CInt(txt_accno.Text), (txt_name.Text), CInt(txt_bal.Text))

            Catch ex As Exception

                MsgBox(ex.Message)
            End Try


        End Sub

        Protected Sub btn_get_Click(sender As Object, e As System.EventArgs) Handles btn_get.Click

            'calling the method getdata to view the output

            Try

                obj.getdata()

            Catch ex As Exception

                MsgBox(ex.Message)
            End Try

        End Sub

        Protected Sub btn_destroy_Click(sender As Object, e As System.EventArgs) Handles btn_destroy.Click

            'calling the constructor

            obj = Nothing

        End Sub
        End Class

如何修复错误“对象引用未设置为对象的实例”？

2 个答案: