c# - 如何在不占用空间的情况下使用 CSS 包含隐藏的 DIV？

Question

我有一个带有单个下拉列表的简单 MVC 5 页面。根据从此下拉列表中所做的选择，我启用了页面上三个 div 之一的可见性。我遇到的问题是每个 div 都会占用页面上的空间，即使它不可见也是如此。因此，当我从下拉列表中选择使第二个 div 可见的内容时，我会看到该内容在页面上向下移动。

下面是来自 Controller 的代码，用于为下拉列表创建数据。

public ActionResult Index()
{
  var searchBy = new List<SearchBy>
  {
    new SearchBy { Name = "Email Address", Value = "EmailAddress" },
    new SearchBy { Name = "Last name, First name", Value = "Name" },
    new SearchBy { Name = "Username", Value = "Username" }
  };

  ViewBag.SearchByOptions = new SelectList(searchBy, "Value", "Name");

  return View();
}

这是我对 Index.cshtml 的标记

@{
<script type="text/javascript">
    $(document).ready(function() {
        // Make all three <div>s hidden when the page loads...
        document.getElementById("searchByEmail").style.visibility = "hidden";
        document.getElementById("searchByName").style.visibility = "hidden";
        document.getElementById("searchByUsername").style.visibility = "hidden";
    });

    function searchBy(selectedItem) {
        if (selectedItem == "EmailAddress") {
            // Make visible
            document.getElementById("searchByEmail").style.visibility = "visible";
            // Make in-visible
            document.getElementById("searchByName").style.visibility = "hidden";
            document.getElementById("searchByUsername").style.visibility = "hidden";
        }                

        if (selectedItem == "Name") {
            // Make visible
            document.getElementById("searchByName").style.visibility = "visible";
            // Make in-visible
            document.getElementById("searchByEmail").style.visibility = "hidden";
            document.getElementById("searchByUsername").style.visibility = "hidden";
        } 

        if (selectedItem == "Username") {
            // Make visible
            document.getElementById("searchByUsername").style.visibility = "visible";
            // Make in-visible
            document.getElementById("searchByEmail").style.visibility = "hidden";
            document.getElementById("searchByName").style.visibility = "hidden";
        }
    };
</script>
}

<h2>Index</h2>
<div>    
    Search for existing users by: @Html.DropDownList("SelectedItem", (SelectList)ViewBag.SearchByOptions, "-- Select One --", new { onchange = "searchBy($('#SelectedItem').val());" }) 
</div>

<div id="searchByEmail">
    Emails...
</div>

<div id="searchByName">
    Names...
</div>

<div id="searchByUsername">
    Usernames...
</div>
}

我不确定需要什么技巧才能让所有 div 在页面上占用相同的“不动产”，因为我一次只显示其中一个。

Answer 1

假设您使用 jQuery，请尝试:

@{
<script type="text/javascript">
    $(document).ready(function() {
        $("#searchByEmail").hide();
        $("#searchByName").hide();
        $("#searchByUsername").hide();
    });

    function searchBy(selectedItem) {
        if (selectedItem == "EmailAddress") {
            $("#searchByEmail").show();
            $("#searchByName").hide();
            $("#searchByUsername").hide();
        }                
        if (selectedItem == "Name") {
            $("#searchByName").show();
            $("#searchByEmail").hide();
            $("#searchByUsername").hide();
        } 

        if (selectedItem == "Username") {
            $("#searchByUsername").show();
            $("#searchByEmail").hide();
            $("#searchByName").hide();
        }
    };
</script>
}

<h2>Index</h2>
<div>    
    Search for existing users by: @Html.DropDownList("SelectedItem", (SelectList)ViewBag.SearchByOptions, "-- Select One --", new { onchange = "searchBy($('#SelectedItem').val());" }) 
</div>

此外，检查 CSS 规则之间的区别:

visibility:hidden

和

display:none

第一个只是隐藏元素，但保留占位符与它可见时相同的大小。第二个将其从大小和尺寸计算中删除。