麻烦高手帮我看看这个页面按了search按钮之后为什么得不出结果(问题一解决立即结帐!)

如题
这个是我用的存储过程:
CREATE PROCEDURE dbo.Searchresult 
@bookname nvarchar(50)=null,
@author  nvarchar(50)=null,
@press nvarchar(50)=null,
@ISBN nvarchar(50)=null
AS
select * 
from Product 
where Product_name like '%'+isnull(@bookname,'')+'%' 
      and Author like '%'+isnull(@author,'')+'%' 
      and Press like '%'+isnull(@press,'')+'%' 
      and ISBN like '%'+isnull(@ISBN,'')+'%'
GO这个是.aspx和后台代码
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>搜索结果</title>  
</head>
<body>
    <form id="form1" runat="server">
        <table border="0" cellpadding="0" cellspacing="0" style="width: 587px" align=center>
            <tr>
                <td colspan="3">
                    <uc1:Top ID="Top1" runat="server" />
                </td>
            </tr>
            <tr>
                <td colspan="3">
                    <img height="5" src="img/spacer.gif" /></td>
            </tr>
            <tr>
                <td colspan="3">
                    <table border="0" cellpadding="0" cellspacing="0" style="font-size: 11pt; width: 833px">
                        <tr>
                            <td colspan="11">
                                <hr style="border-right: #437ac5 1px solid; border-top: #437ac5 1px solid; border-left: #437ac5 1px solid;
                                    border-bottom: #437ac5 1px solid" />
                                <img src="UserControls/img/spacer.gif" /></td>
                        </tr>
                        <tr>
                            <td style="width: 3px">
                                <img height="1" src="img/spacer.gif" width="20" /></td>
                            <td style="width: 51px">
                                按书名:</td>
                            <td>
                                <asp:TextBox ID="TextBox1" runat="server" Height="13px" Width="108px"></asp:TextBox></td>
                            <td>
                                按作者:</td>
                            <td>
                                <asp:TextBox ID="TextBox2" runat="server" Height="13px" Width="108px"></asp:TextBox></td>
                            <td>
                                按出版社:</td>
                            <td>
                                <asp:TextBox ID="TextBox3" runat="server" Height="13px" Width="108px"></asp:TextBox></td>
                            <td>
                                按ISBN:</td>
                            <td style="width: 129px">
                                <asp:TextBox ID="TextBox4" runat="server" Height="13px" Width="108px"></asp:TextBox></td>
                            <td><asp:ImageButton ID="search" runat="server" ImageUrl="~/img/ss.gif" />
                            </td>
                            <td style="width: 2px">
                                <img height="1" src="UserControls/img/spacer.gif" width="20" /></td>
                        </tr>
                        <tr>
                            <td colspan="11">
                                <hr style="border-right: #437ac5 1px solid; border-top: #437ac5 1px solid; border-left: #437ac5 1px solid;
                                    border-bottom: #437ac5 1px solid" />
                                <img src="UserControls/img/spacer.gif" /></td>
                        </tr>
                    </table>
                    <img src="img/spacer.gif" /></td>
            </tr>
            <tr>
                <td colspan="3">
                    <img height="5" src="img/spacer.gif" /></td>
            </tr>
            <tr>
                <td colspan="3">
                    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
                        Width="833px">
                    </asp:GridView>
                    <img src="img/spacer.gif" /></td>
            </tr>
            <tr>
                <td>
                </td>
                <td>
                </td>
                <td>
                </td>
            </tr>
        </table>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:boyabookshopConnectionString %>" SelectCommand="Searchresult" SelectCommandType="StoredProcedure" DataSourceMode="DataReader">
            <SelectParameters>
                <asp:ControlParameter ControlID="TextBox1" Name="bookname"
                    PropertyName="Text" Type="String" ConvertEmptyStringToNull="False" />
                <asp:ControlParameter ControlID="TextBox2" Name="author" PropertyName="Text"
                    Type="String" ConvertEmptyStringToNull="False" />
                <asp:ControlParameter ControlID="TextBox3" Name="press" PropertyName="Text" Type="String" ConvertEmptyStringToNull="False" />
                <asp:ControlParameter ControlID="TextBox4" Name="ISBN" PropertyName="Text" Type="String" ConvertEmptyStringToNull="False" />
            </SelectParameters>        </asp:SqlDataSource>
    </form>
</body>
</html>以下是后台代码:
Partial Class searchresult
    Inherits System.Web.UI.Page    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not TextBox1.Text = "" And TextBox2.Text = "" And TextBox3.Text = "" And TextBox4.Text = "" Then
            GridView1.DataSource = SqlDataSource1
            GridView1.DataBind()
        End If
    End Sub    Protected Sub search_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles search.Click
        If Not TextBox1.Text = "" And TextBox2.Text = "" And TextBox3.Text = "" And TextBox4.Text = "" Then
            GridView1.DataSource = SqlDataSource1
            GridView1.DataBind()
        End If
    End Sub
End Class