网页有错误，null为空或不是对象的问题，请教大家了

Question

i<sourceTb.rows.length;  错在这句,吧html代码也贴出来

Answer 1

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <div style="text-align: center">
        &nbsp;<asp:Label ID="Label1" runat="server" Font-Bold="True" Text="Label"></asp:Label>
        <asp:Label ID="Label2" runat="server" Font-Bold="True" Text="Label"></asp:Label>
        <strong>合同承接明细表测量</strong><br />
                <br />
                <asp:GridView ID="GridView1" runat="server" Font-Bold="False" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" AutoGenerateColumns="False" Width="531px" CellPadding="4" ForeColor="#333333" GridLines="None"
                 OnPageIndexChanging="GridView1_PageIndexChanging" OnRowCancelingEdit="GridView1_RowCancelingEdit" AllowPaging="True" DataKeyNames="Contract_Num">
                    <Columns>
                        <asp:BoundField DataField="Num" HeaderText="序号" />
                        <asp:BoundField DataField="Contract_Num" HeaderText="合同编号" />
                        <asp:BoundField DataField="Contract_Date" HeaderText="签订日期" />
                        <asp:BoundField DataField="Contract_Sum" HeaderText="合同金额" />
                        <asp:BoundField DataField="Contract_Person" HeaderText="经办人" />
                        <asp:BoundField DataField="Res" HeaderText="备注" />
                    </Columns>
                    <EmptyDataTemplate>
                        <table id="tbHeader" style="width: 497px; height: 23px">
                            <tr>
                                <td style="width: 120px; height: 27px">
                                    序号</td>
                                <td style="width: 181px; height: 27px">
                                    合同编号</td>
                                <td style="width: 212px; height: 27px">
                                    签订日期</td>
                                <td style="width: 544px; height: 27px; text-align: center;">
                                    合同金额</td>
                                <td style="width: 173px; height: 27px">
                                    经办人</td>
                                <td style="width: 259px; height: 27px">
                                    备注</td>
                                <td style="width: 212px; height: 27px">
                                </td>
                            </tr>
                        </table>
                    </EmptyDataTemplate>
                    <FooterStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
                    <RowStyle BackColor="#E3EAEB" />
                        <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
                        <PagerStyle BackColor="#666666" ForeColor="White" HorizontalAlign="Center" />
                        <HeaderStyle BackColor="#5BA5C8" Font-Bold="True" ForeColor="White" />
                        <EditRowStyle BackColor="#7C6F57" />
                        <AlternatingRowStyle BackColor="White" />
                </asp:GridView>
        <br />
                <table style="width: 413px" id="tbForm">
                    <tr>
                        <td style="width: 20px; height: 26px;">
                            <asp:TextBox ID="TextBox1" runat="server" Width="70px"></asp:TextBox></td>
                        <td style="width: 99px; height: 26px;">
                            <asp:TextBox ID="TextBox2" runat="server" Width="70px"></asp:TextBox></td>
                        <td style="width: 129px; height: 26px;">
                            <asp:TextBox ID="TextBox3" runat="server" Width="70px"></asp:TextBox></td>
                        <td style="width: 99px; height: 26px;">
                            <asp:TextBox ID="TextBox4" runat="server" Width="92px"></asp:TextBox></td>
                        <td style="width: 81px; height: 26px;">
                            <asp:TextBox ID="TextBox5" runat="server" Width="70px"></asp:TextBox></td>
                        <td style="width: 36px; height: 26px;">
                            <asp:TextBox ID="TextBox6" runat="server" Width="70px"></asp:TextBox></td>
                    </tr>
                    <tr>
                        <td style="width: 20px">
                        </td>
                        <td style="width: 99px">
                        </td>
                        <td style="width: 129px">
                        </td>
                        <td style="width: 99px">
                            <asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" ControlToValidate="TextBox4"
                                Display="Dynamic" ErrorMessage="请输入数字" Font-Size="10pt" ValidationExpression="^-?([1-9]\d*\.\d*|0\.\d*[1-9]\d*|0?\.0+|0)$|^-?\d+$"
                                Width="67px"></asp:RegularExpressionValidator></td>
                        <td style="width: 81px">
                        </td>
                        <td style="width: 36px">
                        </td>
                    </tr>
                </table>
        <br />
        <asp:LinkButton ID="LinkButton1" runat="server" OnClick="LinkButton1_Click" Font-Size="12pt">添加</asp:LinkButton><br />
        <br /><span style="font-size: 12pt">&nbsp; &nbsp;<a href="../measuredval.aspx">返回</a></span>
        &nbsp;</div>
     <script language="javascript">
        function MergeTable(source,dest)
    {
        var row;
        var cell;
        var sourceTb = document.all(source);
        var destTb = document.all(dest);
        for (var i=0; i<sourceTb.rows.length; i++)
        {
             row = document.createElement("TR");
            for (var j=0; j<sourceTb.rows(i).cells.length; j++)
            {
                cell = document.createElement("TD");
                row.appendChild(cell);
                //复制对象
                for(k=0;k<sourceTb.rows(i).cells(j).all.length;k++)
                    cell.appendChild(sourceTb.rows(i).cells(j).all.item(k));
            }
            destTb.tBodies(0).appendChild(row);
        }
        for (var i=sourceTb.rows.length-1; i>=0; i--)
        {
            sourceTb.deleteRow(i)
        }
    }//    function ChangeTableLayout()
//    {
//        if(document.all('tbHeader') == null)
//            MergeTable('tbForm','GridView1');
//        else
//            MergeTable('tbForm','tbHeader');
//    }
    function ChangeTableLayout()
    {
        if(document.all('tbHeader') == null){
         if(document.all('tbForm') != null&&document.all('GridView1') != null)
            MergeTable('tbForm','GridView1');
            else
             alert("tbForm或GridView1不存在!");
        }else{
         if(document.all('tbForm') != null)
            MergeTable('tbForm','tbHeader');
            else
            alert("tbForm不存在!");
        }
    }    ChangeTableLayout();
   </script>
</asp:Content>