当没有从下拉列表中选择值时隐藏/显示表单视图

Question

我的页面中有两个下拉列表、一个详细信息视图和一个表单视图控件。第一个下拉列表具有书籍类别列表，而第二个下拉列表具有基于第一个下拉列表的所选值的书籍列表，最后是显示第二个下拉列表详细信息的详细信息视图。另一方面，表单视图没有任何控件，我只是使用它从详细信息视图中获取值，以便根据第二个选定的下拉列表插入记录。所以我想要做的是，如果第二个下拉列表为空，则隐藏表单视图。

它有点不清楚，但为了简短起见，我只想隐藏表单视图，如果第二个下拉列表中没有选择值（并显示是否有）。

我已附上我的示例代码。我希望你能理解。

提前致谢

<p>
        Book Reservation</p>
    <p>
        <asp:DropDownList ID="DropDownList1" runat="server" AppendDataBoundItems="True" 
            AutoPostBack="True" DataSourceID="categoryDataSource" DataTextField="name" 
            DataValueField="categoryid" >
            <asp:ListItem Selected="True" Value="">-- Choose a category --</asp:ListItem>
        </asp:DropDownList>
        <asp:SqlDataSource ID="categoryDataSource" runat="server" 
            ConnectionString="<%$ ConnectionStrings:LibrarySystemConnectionString %>" 
            SelectCommand="SELECT [categoryid], [name] FROM [TblCategory]" >
        </asp:SqlDataSource>
    </p>
    <p>
        <asp:DropDownList ID="DropDownList2" runat="server"
            AutoPostBack="True" DataSourceID="booktitleDataSource"
            DataTextField="booktitle" DataValueField="bookid" OnDataBound="DetailsView1_DataBound" >
        <asp:ListItem Selected="True" Value="-1">-- Choose a book --</asp:ListItem>
        </asp:DropDownList>

        <asp:SqlDataSource ID="booktitleDataSource" runat="server"
            ConnectionString="<%$ ConnectionStrings:LibrarySystemConnectionString %>" 
            SelectCommand="SELECT [bookid], [booktitle], [categoryid] FROM [TblBooks] WHERE ([categoryid] = @categoryid)">
            <SelectParameters>
                <asp:ControlParameter ControlID="DropDownList1" Name="categoryid" 
                    PropertyName="SelectedValue" Type="Int32" />
            </SelectParameters>
        </asp:SqlDataSource> 
    </p>
    <p>
        <asp:DetailsView ID="DetailsView1" runat="server" AutoGenerateRows="False" 
            DataKeyNames="bookid" DataSourceID="bookdetailsDataSource" >
            <HeaderTemplate>
            <b>BOOK DETAILS</b>
            </HeaderTemplate>

            <FooterTemplate>
            <b>RESERVED BY</b>
            <asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True" 
            AutoGenerateColumns="False" DataKeyNames="reservationid"
            DataSourceID="reserveDataSource">
            <Columns>
            <asp:BoundField DataField="EmployeeID" HeaderText="Employee PIN" 
                    SortExpression="EmployeeID" />

            <asp:BoundField DataField="reservedate" HeaderText="Reserve date" 
                    SortExpression="reservedate" />
            </Columns>
            </asp:GridView>
            <asp:SqlDataSource ID="resereDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:LibrarySystemConnectionString %>"
            SelectCommand="SELECT dbo.BookReservation.reservationid,dbo.BookReservation.bookid, dbo.BookReservation.EmployeeID, 
            dbo.BookReservation.reservedate, dbo.BookReservation.isapproved, dbo.BookReservation.reschedule, dbo.BookReservation.isdeleted, 
            dbo.TblBooks.booktitle FROM dbo.BookReservation INNER JOIN dbo.TblBooks ON dbo.BookReservation.bookid = dbo.TblBooks.bookid WHERE (dbo.BookReservation.isdeleted IS NULL) OR (dbo.BookReservation.deleted = 0)">

            </asp:SqlDataSource>
            </FooterTemplate>
            <Fields>
                <asp:BoundField DataField="bookid" HeaderText="ISBN" ReadOnly="True" 
                    SortExpression="bookid" />
                <asp:BoundField DataField="booktitle" HeaderText="Title" 
                    SortExpression="booktitle" />
                <asp:BoundField DataField="lastname" HeaderText="Author" 
                    SortExpression="lastname" />
                <asp:BoundField DataField="firstname" HeaderText="" 
                    SortExpression="firstname" />
                <asp:BoundField DataField="description" HeaderText="Description" 
                    SortExpression="description" />
                <asp:BoundField DataField="name" HeaderText="Category" 
                    SortExpression="name" />
                <asp:BoundField DataField="quantity" HeaderText="Quantity" 
                    SortExpression="quantity" />
                <asp:BoundField DataField="dateadded" HeaderText="Date added" 
                    SortExpression="dateadded" />
                <asp:CheckBoxField DataField="isdeleted" HeaderText="Deleted" 
                    SortExpression="isdeleted" />
            </Fields>
        </asp:DetailsView>
        <asp:SqlDataSource ID="bookdetailsDataSource" runat="server" 
            ConnectionString="<%$ ConnectionStrings:LibrarySystemConnectionString %>" 
            SelectCommand="SELECT dbo.TblBooks.bookid, dbo.TblBooks.booktitle, dbo.TblBooks.lastname, dbo.TblBooks.firstname, dbo.TblBooks.description, dbo.TblBooks.categoryid, dbo.TblBooks.dateadded, dbo.TblBooks.statusid, dbo.TblBooks.quantity, dbo.TblBooks.isdeleted, dbo.BookStatus.statusname, dbo.TblCategory.name, dbo.LendTable.EmployeeID, dbo.LendTable.dateborrowed, dbo.LendTable.expdateofreturn, dbo.LendTable.datereturned FROM dbo.TblBooks INNER JOIN dbo.TblCategory ON dbo.TblBooks.categoryid = dbo.TblCategory.categoryid INNER JOIN dbo.BookStatus ON dbo.TblBooks.statusid = dbo.BookStatus.statusid INNER JOIN dbo.LendTable ON dbo.TblBooks.bookid = dbo.LendTable.bookid WHERE (dbo.TblBooks.bookid = @bookid) ">
            <SelectParameters>
                <asp:ControlParameter ControlID="DropDownList2" Name="bookid" 
                    PropertyName="SelectedValue" Type="Int64" />
            </SelectParameters>
        </asp:SqlDataSource>
    </p>
    <p>
        <asp:FormView ID="FormView1" runat="server" DataKeyNames="reservationid" 
            DataSourceID="reserveDataSource" DefaultMode="Insert" 
            OnDataBound="FormView1_DataBound" >

            <EditItemTemplate>
                reservationid:
                <asp:Label ID="reservationidLabel1" runat="server" 
                    Text='<%# Eval("reservationid") %>' />
                <br />
                bookid:
                <asp:TextBox ID="bookidTextBox" runat="server" Text='<%# Bind("bookid") %>' />
                <br />
                EmployeeID:
                <asp:TextBox ID="EmployeeIDTextBox" runat="server" 
                    Text='<%# Bind("EmployeeID") %>' />
                <br />
                reservedate:
                <asp:TextBox ID="reservedateTextBox" runat="server" 
                    Text='<%# Bind("reservedate") %>' />
                <br />
                <asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" 
                    CommandName="Update" Text="Update" />
                    &nbsp;<asp:LinkButton ID="UpdateCancelButton" runat="server" 
                    CausesValidation="False" CommandName="Cancel" Text="Cancel" />
            </EditItemTemplate>

            <InsertItemTemplate>

                Reserve date:
                <asp:TextBox ID="reservedateTextBox" runat="server" 
                    Text='<%# Bind("reservedate") %>' />
                <a href="#" onclick="cdp1.showCalendar(this, 'ctl00$ContentPlaceHolder1$FormView1$reservedateTextBox'); return false;">Date Picker</a>
                <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="reservedateTextBox" ErrorMessage="* " ValidationGroup="reservebook">
                </asp:RequiredFieldValidator>
                <br />

                <asp:Button ID="InsertButton" runat="server" CausesValidation="True" 
                    CommandName="Insert" Text="Insert" />
                    &nbsp;<asp:Button ID="InsertCancelButton" runat="server" 
                    CausesValidation="False" CommandName="Cancel" Text="Cancel" />

                <%--ISBN:--%>
                <asp:TextBox ID="bookidTextBox" runat="server" Visible="false" 
                    Text='<%# Bind("bookid") %>' />
                <br />
                <%--Employee PIN:--%>
                <asp:TextBox ID="EmployeeIDTextBox" runat="server" Visible="false" 
                    Text='<%# Bind("EmployeeID") %>' />
                <br />

            </InsertItemTemplate>

Answer 1

1) 最初从标记设置 FromView Visible="False"。
2) 将 OnSelectedIndexChanged="DropDownList2_SelectedIndexChanged" 分配给 DropDownList2 并设置其 AutoPostBack="True"

3) 在后面的代码中添加以下内容：

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
    if(!DropDownList2.SelectedValue.Equals("-1"))
        FromView1.Visible=true;
    else
        FromView1.Visible=false;
}