尝试将值插入本地数据库时出现运行时错误

Question

return new Dismissible(
                       key: new Key(mainList[index].id.toString()),
                        direction: DismissDirection.horizontal,
                        resizeDuration: null,
                        background: new LeaveBehindViewArchive(),
                        secondaryBackground: new LeaveBehindViewDelete(),
                        dismissThresholds: _dismissThresholds(),
                        onDismissed: (DismissDirection direction) {
                          if (direction == DismissDirection.startToEnd){
                              _setArchiveWhenSwipe(mainList[index]);
                              handleUndo(mainList[index]);
                          } else if (direction ==
                              DismissDirection.endToStart) {
                            setDelete(mainList[index]);
                          }
                        },
 )

C＃代码：

<asp:TextBox ID="txtfrname" runat="server" placeholder="First Name" Height="25px" Width="250px">
<asp:TextBox ID="txtlaname" runat="server" placeholder="Last Name" Height="25px" Width="250px" />
<asp:TextBox ID="txtmob" runat="server" placeholder="Mobile Number" TextMode="Number" Height="25px" Width="250px"></asp:TextBox>
<asp:Button ID="Signup" runat="server" Class="btn" OnClientClick="validate()" OnClick="Signup_Click" Text="Register" style="width:120px; height:35px;font-weight:normal;font-family:Arial; font-size:small; color:white; background-color:#ff4500; border-width:0PX; border-style:None" onmouseover="this.style.backgroundColor='#ff6933';return true;"  onmouseout="this.style.backgroundColor='#ff4500'; return true;" />