防止在detailview ASP.NET C＃中插入null

Question

我有一个带有插入按钮的DetailsView，我想阻止插入空值，但我不想使用RequiredFieldsValidator。

我有以下代码，但我不知道应该把它放在哪里，因为我想在保存到数据库之前显示任何空文本框时显示错误消息

TextBox txt1 = (TextBox)DetailsView2.FindControl("TextBox1") as TextBox;

 if (txt1.Text == "")
 {
    string message = "Please Fill All the Fields";
    System.Text.StringBuilder sb = new System.Text.StringBuilder();
    sb.Append("<script type = 'text/javascript'>");
    sb.Append("window.onload=function(){");
    sb.Append("alert('");
    sb.Append(message);
    sb.Append("')};");
    sb.Append("</script>");
    ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", sb.ToString());
 }

DetailsView代码

<asp:DetailsView ID="DetailsView2" runat="server" AutoGenerateRows="False" 
        CellPadding="4" DataKeyNames="Username" DataSourceID="SqlDataSource1" 
        ForeColor="#333333" GridLines="None" Height="50px" 
        Width="231px" style="margin-top: 0px; text-align: left;" 
        onitemupdated="DetailsView2_ItemUpdated" DefaultMode="Insert" 
        onitemdeleted="DetailsView2_ItemDeleted" 
        oniteminserted="DetailsView2_ItemInserted" 
        ondatabinding="DetailsView2_DataBinding">
        <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
        <CommandRowStyle BackColor="#E2DED6" Font-Bold="True" />
        <EditRowStyle BackColor="#999999" />
        <FieldHeaderStyle BackColor="#E9ECF1" Font-Bold="True" />
        <Fields>
            <asp:TemplateField HeaderText="Username" SortExpression="Username">
                <EditItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Eval("Username") %>'></asp:Label>
                </EditItemTemplate>
                <InsertItemTemplate>
                    <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("Username") %>'></asp:TextBox>
                </InsertItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label2" runat="server" Text='<%# Bind("Username") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Password" SortExpression="Password">
                <EditItemTemplate>
                    <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("Password") %>'></asp:TextBox>
                </EditItemTemplate>
                <InsertItemTemplate>
                    <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("Password") %>'></asp:TextBox>
                </InsertItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label3" runat="server" Text='<%# Bind("Password") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="UserType" SortExpression="UserType">
                <EditItemTemplate>
                    <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("UserType") %>'></asp:TextBox>
                </EditItemTemplate>
                <InsertItemTemplate>
                    <asp:DropDownList ID="DropDownList1" runat="server" SelectedValue='<%# Bind("UserType") %>'>
                    <asp:ListItem>--Select--</asp:ListItem>
                    <asp:ListItem>employee</asp:ListItem>
                    <asp:ListItem>doctor</asp:ListItem>
                    <asp:ListItem>student</asp:ListItem>
                    </asp:DropDownList>
                </InsertItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("UserType") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:CommandField ButtonType="Button" ShowInsertButton="True" />
        </Fields>
        <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
        <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
        <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
        <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
    </asp:DetailsView>