案件背景：

工作中的一個報表之前一直工作正常，但是有一天突然使用者開啟報錯，提示view state 無效。檢查程式碼發現沒有問題，檢查前臺頁面後發現報表顯示後的viewstate大小居然達到40M以上。

通過在頁面增加下面兩個事件的程式碼，把view state 儲存到文字檔案中。可以讓頁面顯示速度大大提高。

VB.NET 版

    Protected Overrides Sub SavePageStateToPersistenceMedium(ByVal state As Object)
        Dim x As New ObjectStateFormatter()
        Dim value As String = x.Serialize(state)
        Dim viewStateID As String = DateTime.Now.Ticks + Me.GetHashCode().ToString
        Dim fn As String = System.IO.Path.Combine(Request.PhysicalApplicationPath, "App_Data/ViewState/" + viewStateID)
        System.IO.File.WriteAllText(fn, value)
        Cache.Insert(viewStateID, value)
        MyBase.SavePageStateToPersistenceMedium(viewStateID)
    End Sub
 

    Protected Overrides Function LoadPageStateFromPersistenceMedium() As Object
        Dim viewStateID As String
        viewStateID = CType(MyBase.LoadPageStateFromPersistenceMedium, Pair).Second.ToString
        Dim stateStr As String = ""
        Dim result As New Object
        If Cache(viewStateID) IsNot Nothing Then
            stateStr = Cache(viewStateID).ToString()
        End If


        If stateStr.ToString.Equals("") = False Then
            Dim fn As String = System.IO.Path.Combine(Request.PhysicalApplicationPath, "App_Data/ViewState/" + viewStateID)
            stateStr = System.IO.File.ReadAllText(fn)
        End If
        Dim x As New ObjectStateFormatter()
        If stateStr.Equals("") = False Then
            result = x.Deserialize(stateStr)
        End If
        Return result


    End Function
 

C# 版

    Protected Overrides Sub SavePageStateToPersistenceMedium(ByVal state As Object)

        string value = new ObjectStateFormatter().Serialize(state);
        string viewStateID = (DateTime.Now.Ticks + (long)this.GetHashCode()).ToString(); //產生離散的id號碼
        string fn = Path.Combine(this.Request.PhysicalApplicationPath, @"App_Data/ViewState/" + viewStateID);
        //ThreadPool.QueueUserWorkItem(File.WriteAllText(fn, value));
        File.WriteAllText(fn, value); 
        Cache.Insert(viewStateID, value);
        base.SavePageStateToPersistenceMedium(viewStateID);

    End Sub