Avoid submit event Refresh in Asp.net

'Declare variables for use

    Private _refreshState As Boolean

    Private _isRefresh As Boolean

'Functions to Use

#Region " ISREFRESH "

    Protected Overrides Sub LoadViewState(ByVal savedState As Object)

        Dim AllStates As Object() = savedState

        MyBase.LoadViewState(AllStates(0))

        _refreshState = Boolean.Parse(AllStates(1))

        _isRefresh = _refreshState = Session("__ISREFRESH")

    End Sub

    Protected Overrides Function SaveViewState() As Object

        Session("__ISREFRESH") = _refreshState

        Dim AllStates() As Object = New Object(2) {}

        AllStates(0) = MyBase.SaveViewState

        AllStates(1) = Not (_refreshState)

        Return AllStates

    End Function

#End Region

'Call function in Button Click Event

Protected Sub btnLogin_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles btnLogin.Click

      If _isRefresh = True Then

            Exit Sub

      End If

End Sub