inject code into masterpage / html head from a user control_问答_开发者

I am struggling with something that I guess should be standard practice really. I have a number of user controls that use some JQuery plugins. I do not really want to link to the extra CSS and JS files from my main masterpage as this would cause extra load to the user the first time they hit the site, (admittedly it would only be the once), so I was just putting them links into the top of the user control. Then I looked at my开发者_如何学JAVA source HTML, not nice! Even worse for controls that repeat multiple times on a page.

So I was thinking is there a way of injecting them into the Head of the page when they are needed from the User Control. For that matter is there a way of doing it to the footer for JS stuff?

To dynamically register a script (and ensure that duplicates are merged) in ASP.NET you can call:

Page.ClientScript.RegisterClientScriptInclude(
    "mykey", "~/scripts/jquery-1.3.2.js");

And read the full details on this method on MSDN.

To add CSS dynamically you can do something like this:

HtmlLink cssLink = new HtmlLink();
cssLink.Href = "path to CSS";
cssLink.Attributes["some attr1"] = "some value1";
cssLink.Attributes["some attr2"] = "some value2";
Page.Header.Controls.Add(cssLink);

This example of injecting CSS will not merge duplicate entries. To avoid duplication you'll have to keep track of duplicates yourself. One place you can store a list of scripts you've already registered is in HttpContext.Items. Stick a HashSet in there that keeps a list of all registered scripts so that you don't register the same CSS file twice (which is generally harmless, but something to avoid anyway).

I followed a similar approach, but I use CSS directly in the user control so I don't have to import a CSS file. The following is code entirely from a sample user control:

<style id="style1" type="text/css" visible="false" runat="server">
    td { font-family: Tahoma; font-size: 8pt; }
</style>

In code-behind:

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);

    HtmlGenericControl style = new HtmlGenericControl("style");
    style.Attributes.Add("type", "text/css");
    style.InnerHtml = style1.InnerHtml;
    Page.Header.Controls.Add(style);
}

You'll notice that the CSS is rendered in the head tag and not inside the body tag.

You can use ClientScript.RegisterClientScriptInclude() for the JavaScript.

For the CSS, one trick is to include them in your Master page, but with Visible="false", so that they aren't rendered into the markup by default.

Then, in your user controls, set a flag in the Items collection, from an early event, such as OnLoad(). For example, this.Context.Items["mycss"] = true;

Finally, in your Master page, from a later event, such as OnPreRender(), check to see if those flags are set. If they are, then set the Visible property to true for the corresponding CSS.

This also allows you to use the control with Master pages that don't use the CSS, since the Items entries could simply be ignored. If you have many Master pages that need the same behavior, you could put this code in a base class or use nested Master pages.

I assume you're using Asp.NET.

Try putting a content placeholder in the of the MasterPage...

<head>
<asp:ContentPlaceHolder ID="AdditionalPageHeader" />
</head>

If you're working in an aspx file or an ascx you need only define a content control...

<asp:Content ContentPlaceHolderID="AdditionalPageHeader" />

If you're working on a code-behind only type of server control, you can can get a pointer to that content place holder:

this.Page.Master.FindControl("AdditionalPageHeader")

... and manipulate it's contents programatically.

To add stylesheets or javascript (inline or not) dynamical I wrote these three functions:

  Public Function addScript(ByVal path2js As String) As System.Web.UI.Control
    Dim si As New HtmlGenericControl
    si.TagName = "script"
    si.Attributes.Add("type", "text/javascript")
    si.Attributes.Add("src", path2js)
    Return si
  End Function
  Public Function addScript_inline(ByVal js As String) As System.Web.UI.Control
    Dim si As New HtmlGenericControl
    si.TagName = "script"
    si.Attributes.Add("type", "text/javascript")
    si.InnerHtml = js
    Return si
  End Function
  Public Function addStyle(ByVal path2css As String) As System.Web.UI.Control
    Dim css As New HtmlLink
    css.Href = path2css
    css.Attributes.Add("rel", "stylesheet")
    css.Attributes.Add("type", "text/css")
    css.Attributes.Add("media", "all")
    Return css
  End Function

I call them in page_load on my masterpage, like this:

Me.Page.Header.Controls.Add(modGlobal.addScript("script/json/json2.js"))

Me.Page.Header.Controls.Add(modGlobal.addStyle("style/flexigrid/flexigrid.css"))

Regards

inject code into masterpage / html head from a user control

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