Question

学习ASP。得到了这个问题，制作了9个图像按钮，并希望用相同的处理程序处理它们：

    protected void jugar_Click(object sender, ImageClickEventArgs e)
    {
        String turno = (string)Session["Turno"];
        ImageButton boton = (ImageButton)sender;
        if (turno == "1")
        {
            boton.ImageUrl = "C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\Tic-tac-toe-cross.png";
            Session["Turno"] = 2;
        }
        else if (turno == "2")
        {
            boton.ImageUrl = "C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\Tic-tac-toe-nought-e1461667111145.png";
            Session["Turno"] = 1;
        }
    }

抛出一个施法异常，

有什么想法错了吗？

这些是引用此处理程序的按钮：

    <asp:Table ID="Table2" runat="server" HorizontalAlign="Center">
        <asp:TableRow runat="server">
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" Style="border-bottom: solid 2px red; border-right: solid 2px red">
                <asp:ImageButton ID="btn00" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-left:solid 2px red;border-bottom:solid 2px red;border-right:solid 2px red">
                <asp:ImageButton ID="btn01" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-left:solid 2px red;border-bottom:solid 2px red">
                <asp:ImageButton ID="btn02" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
        </asp:TableRow>
        <asp:TableRow runat="server">
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-bottom:solid 2px red;border-right:solid 2px red">
                <asp:ImageButton ID="btn10" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-bottom:solid 2px red;border-left:solid 2px red;border-right:solid 2px red">
                <asp:ImageButton ID="btn11" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-bottom:solid 2px red;border-left:solid 2px red">
                <asp:ImageButton ID="btn12" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
        </asp:TableRow>
        <asp:TableRow runat="server">
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-right:solid 2px red">
                <asp:ImageButton ID="btn20" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-left:solid 2px red;border-right:solid 2px red">
                <asp:ImageButton ID="btn21" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
            <asp:TableCell runat="server" Height="100" Width="100" HorizontalAlign="Center" VerticalAlign="Middle" style="border-top:solid 2px red;border-left:solid 2px red">
                <asp:ImageButton ID="btn22" runat="server" class="imagen" ImageUrl="C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\White_square.jpg" OnClick="jugar_Click"></asp:ImageButton>
            </asp:TableCell>
        </asp:TableRow>
    </asp:Table>

抱歉缺少信息，我是新手

Answer 1

很可能这一行会根据您发布的代码抛出异常ImageButton boton = (ImageButton)sender; ...如果是，则sender绝对不是ImageButton而是其他一些控件类型

Answer 2

protected void jugar_Click(object sender, ImageClickEventArgs e) {

 if (sender is ImageButton) {

  var turNo = Session["Turno"];

  var buttonSender = (ImageButton)sender;

  switch (turNo) {
   case 1:
    buttonSender.ImageUrl = "C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\Tic-tac-toe-cross.png";
    Session["Turno"] = 2;
    break;
   case 2:
    buttonSender.ImageUrl = "C:\Users\Epyros\documents\visual studio 2015\Projects\EnTA TE TI\EnTA TE TI\Imagenes\Tic-tac-toe-nought-e1461667111145.png";
    Session["Turno"] = 1;
    break;
   default:
    // Logic for turNo != 1 or 2
    break;
  }
 }
 else
 {
     // sender is not the expected type (ImageButton)
     Trace.WriteLine(string.Format("Sender is an unexpected type. Expected: (ImageButton), got ({0}).", sender.GetType().Name),"WARN");
 }
}

此代码可以防止您遇到强制转换异常，并告知您作为罪魁祸首的发件人类型。

在事件单击处理程序上强制转换异常

2 个答案: