如何写事件代码？

Question

以下是一个联合使用GridView和DetailsView控件的实例代码，DetailsView可以插入新的记录，但由于数据表的主键(CustomerID)为字符型的，最多5个字符，且不能输入重复值，如果我想实现当用户提交新记录时发现有重复值或值过长的情况时系统可以捕捉并提示报警信息的话，应该在哪个控件的什么事件上写代码，如何写呢？谢谢！<form id="form1" runat="server">
    <div>
        <asp:GridView ID="GridView1" runat="server" AllowPaging="True" AutoGenerateColumns="False"
            AutoGenerateSelectButton="True" BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None"
            BorderWidth="1px" CellPadding="3" CellSpacing="2" DataKeyNames="CustomerID" DataSourceID="SqlDataSource1"
            PageSize="5">
            <FooterStyle BackColor="#F7DFB5" ForeColor="#8C4510" />
            <PagerStyle ForeColor="#8C4510" HorizontalAlign="Center" />
            <HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" />
            <Columns>
                <asp:BoundField DataField="CustomerID" HeaderText="CustomerID" ReadOnly="True" SortExpression="CustomerID" />
                <asp:BoundField DataField="CompanyName" HeaderText="CompanyName" SortExpression="CompanyName" />
                <asp:BoundField DataField="ContactName" HeaderText="ContactName" SortExpression="ContactName" />
                <asp:BoundField DataField="ContactTitle" HeaderText="ContactTitle" SortExpression="ContactTitle" />
                <asp:BoundField DataField="Address" HeaderText="Address" SortExpression="Address" />
                <asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />
                <asp:BoundField DataField="Region" HeaderText="Region" SortExpression="Region" />
                <asp:BoundField DataField="PostalCode" HeaderText="PostalCode" SortExpression="PostalCode" />
                <asp:BoundField DataField="Country" HeaderText="Country" SortExpression="Country" />
                <asp:BoundField DataField="Phone" HeaderText="Phone" SortExpression="Phone" />
                <asp:BoundField DataField="Fax" HeaderText="Fax" SortExpression="Fax" />
            </Columns>
            <SelectedRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="White" />
            <RowStyle BackColor="#FFF7E7" ForeColor="#8C4510" />
        </asp:GridView>
        <p>
            <b>Customer Details:</b></p>
        <asp:DetailsView ID="DetailsView1" runat="server" AutoGenerateInsertButton="true"
            AutoGenerateRows="False" BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None"
            BorderWidth="1px" CellPadding="3" CellSpacing="2" DataKeyNames="CustomerID" DataSourceID="SqlDataSource2">
            <FooterStyle BackColor="#F7DFB5" ForeColor="#8C4510" />
            <RowStyle BackColor="#FFF7E7" ForeColor="#8C4510" />
            <PagerStyle ForeColor="#8C4510" HorizontalAlign="Center" />
            <Fields>
                <asp:BoundField DataField="CustomerID" HeaderText="CustomerID" ReadOnly="True" SortExpression="CustomerID" />
                <asp:BoundField DataField="CompanyName" HeaderText="CompanyName" SortExpression="CompanyName" />
                <asp:BoundField DataField="ContactName" HeaderText="ContactName" SortExpression="ContactName" />
                <asp:BoundField DataField="ContactTitle" HeaderText="ContactTitle" SortExpression="ContactTitle" />
                <asp:BoundField DataField="Address" HeaderText="Address" SortExpression="Address" />
                <asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />
                <asp:BoundField DataField="Region" HeaderText="Region" SortExpression="Region" />
                <asp:BoundField DataField="PostalCode" HeaderText="PostalCode" SortExpression="PostalCode" />
                <asp:BoundField DataField="Country" HeaderText="Country" SortExpression="Country" />
                <asp:BoundField DataField="Phone" HeaderText="Phone" SortExpression="Phone" />
                <asp:BoundField DataField="Fax" HeaderText="Fax" SortExpression="Fax" />
            </Fields>
            <HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" />
            <EditRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="White" />
        </asp:DetailsView>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
            SelectCommand="SELECT * FROM [Customers]"></asp:SqlDataSource>
        <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
            DeleteCommand="DELETE FROM [Customers] WHERE&#13;&#10;                 [CustomerID] = @original_CustomerID"
            FilterExpression="CustomerID='{0}'" InsertCommand="INSERT INTO [Customers] ([CustomerID], [CompanyName],&#13;&#10;                 [ContactName], [ContactTitle], [Address], [City], [Region], [PostalCode], &#13;&#10;                 [Country], [Phone], [Fax]) VALUES (@CustomerID, @CompanyName,&#13;&#10;                 @ContactName, @ContactTitle, @Address, @City, @Region, @PostalCode,&#13;&#10;                 @Country, @Phone, @Fax)"
            SelectCommand="SELECT * FROM [Customers]">
            <FilterParameters>
                <asp:ControlParameter ControlID="GridView1" Name="CustomerID" PropertyName="SelectedValue" />
            </FilterParameters>
            <InsertParameters>
                <asp:Parameter Name="CustomerID" Type="String" />
                <asp:Parameter Name="CompanyName" Type="String" />
                <asp:Parameter Name="ContactName" Type="String" />
                <asp:Parameter Name="ContactTitle" Type="String" />
                <asp:Parameter Name="Address" Type="String" />
                <asp:Parameter Name="City" Type="String" />
                <asp:Parameter Name="Region" Type="String" />
                <asp:Parameter Name="PostalCode" Type="String" />
                <asp:Parameter Name="Country" Type="String" />
                <asp:Parameter Name="Phone" Type="String" />
                <asp:Parameter Name="Fax" Type="String" />
            </InsertParameters>
        </asp:SqlDataSource>

Answer 1

(写个伪码表达意思)在插入事件中加入:
try
{
  if(inputtxt > yourrequireLength) throw new ApplicationException("Too long!")
  //其他判定逻辑的代码放这里，当然也可以把这些逻辑放到独立的函数中并在此调用该函数
  // 插入你的数据的代码放这里
  //...
}
catch(Exception err)
{
   Response.Redirect("ErrorPage.aspx?...");
}