如何在ASP.NET中通过Class而不是ID选择一个元素？ [英] How to select an element by Class instead of ID in ASP.NET?

问题描述

我在aspx页面上有一些散布的< p> 元素，我使用类 - < p class =instructionsrunat =server>

在我的代码中，使用C＃我想隐藏这些元素，像
instructions.Visible = false;

但是我意识到我只能在codebehind if我使用ID，但这将导致无效的HTML / CSS选择器，因为您不能有多个ID具有相同的ID名称...

或者有另一种方法如果不是按类分组控件？

编辑：我不能使用JavaScript，所以选择必须在C＃codebehind / ASP.NET

解决方案

除了将单个容器控件中的所有控件分组之外，没有简单的方法来找到一组给定ASP中的属性的控件。 NET服务器端代码。

在客户端，您可以使用 jQuery 找到这些元素并隐藏它们：

  $（。 
  

我可能会在页面完全加载时做出响应：

  $（document）.ready（function（）{
 $（instructions）。hide（）; 
} ; 
 

在Javascript中隐藏元素的一个缺点是，如果有足够的数据，可能需要一秒钟，闪烁。另一个区别是，隐藏内容客户端不会从DOM中删除它 - 内容刚刚隐藏。隐藏控件服务器端阻止其内容甚至被发送到HTML。

在C＃中做同样的事情有点困难 - 它需要递归遍历控制树和在匹配的 Control 集合中查找元素。这是一个足够普遍的操作，效用函数是有用的。 C＃迭代器语法（yield return）有助于使得这个干净：

  //实用方法递归地找到匹配谓词的控制
 IEnumerable& FindRecursive（Control c，Func< Control，bool>谓词）
 {
 if（谓词（c））
 yield return c; 
 
 foreach（c.Controls中的var子项）
 {
 if（谓词（c））
 yield return c; 
} 
 
 foreach（c.Controls中的var child）
 foreach（FindRecursive（c，predicate）中的var匹配）
 yield return match; 
} 
 
 //使用实用程序方法来查找匹配的控件... 
 FindRecursive（Page，c =>（c是WebControl）&& 
（（WebControl）c）.CssClass ==instructions）; 
 

现在隐藏控件相对容易：

  foreach（WebControl c in FindRecursive（Page，c =>（c是WebControl）&& 
（（WebControl）c）.CssClass ==instructions ））
 {
 c.Visible = false; 
} 
  




I have a few scattered <p> elements on the aspx page which I am grouping together using a class like so - <p class="instructions" runat="server">

In my code behind, using C# I want to hide these elements, using something like instructions.Visible = false;

However I realize I can only do this in codebehind if I use ID but this will result in invalid HTML/CSS Selector since you can't have multiple ID's with the same ID name...

Alternatively is there another way to group the controls if not by class?

EDIT: I can't use JavaScript, so the selection must be done in C# codebehind/ASP.NET

解决方案

Aside from grouping all of the controls in a single container control, there is no easy way to find a group of controls given some property in ASP.NET server-side code.

On the client side, you could use something like jQuery to find these elements and hide them:

$(".instructions").hide();

I would probably do this in response when the page is fully loaded:

$(document).ready(function() { 
   $(".instructions").hide(); 
});

One downside to hiding elements in Javascript is that if there's enough data it may take a second and cause content to flicker. Another difference is that hiding content client-side does not remove it from the DOM - the content is there just hidden. Hiding controls server-side prevents their content from even being emitted to the HTML.

Doing the same thing in C# is a bit harder - it requires recursively traversing the control tree and looking for elements in the Control collection that match. This is a common enough operation that a utility function is useful. C# iterator syntax (yield return) is helpful in making this clean:

// utility method to recursively find controls matching a predicate
IEnumerable<Control> FindRecursive( Control c, Func<Control,bool> predicate )
{
    if( predicate( c ) )
        yield return c;

    foreach( var child in c.Controls )
    {
        if( predicate( c ) )
            yield return c;
    }

    foreach( var child in c.Controls )
        foreach( var match in FindRecursive( c, predicate ) )
           yield return match;
}

// use the utility method to find matching controls...
FindRecursive( Page, c => (c is WebControl) && 
                          ((WebControl)c).CssClass == "instructions" );

Hiding the controls now is relatively easy:

foreach( WebControl c in FindRecursive( Page, c => (c is WebControl) && 
                           ((WebControl)c).CssClass == "instructions" ) )
{
    c.Visible = false;
}

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