ASP.NET Using VB.NET - Button event handler not fired and the text box value not stored when navigating to another pages

Actually i am just learning asp.net. Well i have a little problem with asp.net web page. I have 2 web forms, WebForm1 with just a single DataGrid control, and WebForm2 with a pair of Label and TextBox, and 2 Buttons. Well straight to the point, here is my code for WebForm1:

Imports System.Configuration.ConfigurationManager
Imports System.Data.SqlClient

Public Class WebForm1
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim strConn As String = ConnectionStrings("ConnStr").ConnectionString
        Dim sqlConn As SqlConnection = New SqlConnection(strConn)
        Dim sqlComd As SqlCommand = New SqlCommand
        Dim sqlRead As SqlDataReader = Nothing
        Dim sqlParm As SqlParameter

        sqlParm = New SqlParameter("@Criteria", SqlDbType.NVarChar, 50)
        sqlParm.Value = ""

        sqlComd.Connection = sqlConn
        sqlComd.CommandText = "ShowCategory"
        sqlComd.Parameters.Add(sqlParm)
        sqlComd.CommandType = CommandType.StoredProcedure

        Try
            sqlConn.Open()
            sqlRead = sqlComd.ExecuteReader()
            grdCategory.DataSource = sqlRead
            grdCategory.DataBind()
        Catch ex As Exception
            Throw ex
        Finally
            sqlConn.Close()
        End Try
    End Sub

    Private Sub grdCategory_SelectedIndexChanged(sender As Object, e As EventArgs) Handles grdCategory.SelectedIndexChanged
        Server.Transfer("~/WebForm2.aspx", False)
    End Sub
End Class

And here is my code for WebForm2:

Imports System.Configuration.ConfigurationManager
Imports System.Data.SqlClient

Public Class WebForm2
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            Dim prevPage As Page = Me.Page.PreviousPage
            If prevPage IsNot Nothing Then
                Dim ctn As ContentPlaceHolder = CType(prevPage.Master.FindControl("MainContent"), ContentPlaceHolder)
                Dim grd As GridView = CType(ctn.FindControl("grdCategory"), GridView)
                ViewState("ID") = grd.SelectedRow.Cells(1).Text
                txtName.Text = grd.SelectedRow.Cells(2).Text
                txtDesc.Text = grd.SelectedRow.Cells(3).Text
            End If
        End If
    End Sub

    Protected Sub btnBack_Click(sender As Object, e As EventArgs) Handles btnBack.Click
        Response.Redirect("~/WebForm1.aspx")
    End Sub

    Protected Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
        Dim strConn As String = ConnectionStrings("ConnStr").ConnectionString
        Dim sqlConn As SqlConnection = New SqlConnection(strConn)
        Dim sqlComd As SqlCommand = New SqlCommand
        Dim sqlParm(2) As SqlParameter

        sqlParm(0) = New SqlParameter("@CategoryID", SqlDbType.Int, 0)
        sqlParm(1) = New SqlParameter("@CategoryName", SqlDbType.NVarChar, 15)
        sqlParm(2) = New SqlParameter("@Description", SqlDbType.NText)

        sqlParm(0).Value = ViewState("ID").ToString
        sqlParm(1).Value = txtName.Text.Trim
        sqlParm(2).Value = txtDesc.Text.Trim

        sqlComd.Parameters.AddRange(sqlParm)
        sqlComd.CommandText = "InsertCategory"
        sqlComd.CommandType = CommandType.StoredProcedure

        Try
            sqlConn.Open()
            sqlComd.ExecuteNonQuery()
        Catch ex As Exception
            Throw ex
        Finally
            sqlConn.Close()
        End Try
    End Sub
End Class

The logic is, I select a row in datagrid control and pass the values of the selected row to the textbox control in WebForm2.

The problem is, after I change the value of the textbox and I press save button, the btnSave_Click did not executed and it seem the value of the textbox did not change too. I try debugging, and after I press the save button, it execute the page_load event and did not execute the btnSave_Click event.

The questions, is anyone know the reason why the btnSave_Click event did not executed, and how to fix it, so the btnSave_Click can executed after I press the button. Thank you before and sorry for my bad english.