I was wondering if its possible to have an ASP.NET AJAX custom usercontrol 'register' its use of CSS files like it does with JS files. ?
Eg: Implementing the IScriptControl interface allows for the GetScriptReferences() to be called by the Script Manager, is there a similar thing for CSS files?
No.
You could write your own methods to use embedded resources and generate html to write them to the page.
As a best-practice approach, though, I wouldn't recommend this. You should have a clear separation of style and markup. If you want to write a custom control that is dependent on a stylesheet, then I suggest that you provide a default css file along with your control.
EDIT (to answer questions in the comments)
You can run this code to add a reference to the CSS file to your page (at runtime). Note that because you're using the RegisterClientScriptBlock method, you can manage insert duplication. Here is an excerpt from the link for the method:
A client script is uniquely identified by its key and its type. Scripts with the same key and type are considered duplicates. Only one script with a given type and key pair can be registered with the page. Attempting to register a script that is already registered does not create a duplicate of the script.
StringBuilder sb = new StringBuilder();
sb.Append(#"<link rel=""stylesheet"" type=""text/css"" href=""");
sb.Append(this.Page.ClientScript.GetWebResourceUrl(this.GetType(), resourceName));
sb.Append(#""" />");
this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "MyCSS", sb.ToString());
Related
As a web developer I feel too much of my time is spent on CSS. I am trying to come up with a solution where I can write re-usable CSS i.e. classes and reference these classes in the HTML without additional code in ASPX or ASCX files etc. or code-behind files. I want an intermediary which links up HTML elements with CSS classes.
What I want to achieve:
Modify HTML immediately before transmission
Select elements in the HTML
Based on rules defined elsewhere (e.g. in a text file relating to
the page currently being processed):
Add a CSS class reference to multiple HTML elements
Add multiple CSS class references to a single HTML element
How I envisage this working:
Extend ASP.NET functions which generate final HTML
Grab all the HTML as a string
Pass the string into a contructor for an object with querying (e.g. XPATH) methods
Go through list of global rules e.g. for child ul of first div then class = "navigation"
Go through list of page specific rules e.g. for child ul of first div then class &= " home"
Get processed HTML from object e.g. obj.ToString
ASP.NET to resume page generation using processed HTML
So what I need to know is:
Where / how can I extend ASP.NET page generation functions (to get all HTML of page)
What classes have element / node querying methods and access to attributes
Thanks for your help in advance.
P.S. I am developing ASP.NET web forms websites with VB.net code-behinds running on ISS 7
Check out my CsQuery project: https://github.com/jamietre/csquery or on nuget as "CsQuery".
This is a C# (.NET 4) port of jQuery. In basic performance tests (included in the project test suite) selectors are about 100 times faster than HTML Agility Pack + Fizzler (a css selector add-on for HAP); it's plenty fast for manipulating the output stream in real time on a typical web site. If you are amazon.com or something, of course, YMMV.
My initial purpose in developing this was to manipulate HTML from a content management system. Once I had it up and running, I found that using CSS selectors and the jQuery API is a whole lot more fun than using web controls and started using it as a primary HTML manipulation tool for server-rendered pages, and built it out to cover pretty much all of CSS, jQuery and the browser DOM. I haven't touched a web control since.
To intercept HTML in webforms with CsQuery you do this in the page codebehind:
using CsQuery;
using CsQuery.Web;
protected override void Render(HtmlTextWriter writer)
{
var csqContext = WebForms.CreateFromRender(Page, base.Render, writer);
// CQ object is like a jQuery object. The "Dom" property of the context
// returned above represents the output of this page.
CQ doc = csqContext.Dom;
doc["li > a"].AddClass("foo");
// write it
csqContext.Render();
}
To do the same thing in ASP.NET MVC please see this blog post describing that.
There is basic documentation for CsQuery on GitHub. Apart from getting HTML in and out, it works pretty much like jQuery. The WebForms object above is just to help you handle interacting with the HtmlTextWriter object and the Render method. The general-purpose usage is very simple:
var doc = CQ.Create(htmlString);
// or (useful for scraping and testing)
var doc = CQ.CreateFromUrl(url);
// do stuff with doc, a CQ object that acts like a jQuery object
doc["table tr:first"].Append("<td>A new cell</td>");
Additonally, pretty much the entire browser DOM is available using the same methods you use
in a browser. The indexer [0] returns the first element in the selection set like jquery; if you are used to write javascript to manipulate HTML it should be very familiar.
// "Select" method is the same as the property indexer [] we used above.
// I go back and forth between them to emphasise their interchangeability.
var element = dom.Select("div > input[type=checkbox]:first-child")[0];
a.Checked=true;
Of course in C# you have a wealth of other general-purpose tools like LINQ at your disposal. Alternatively:
var element = dom["div > input[type=checkbox]:first-child"].Single();
a.Checked=true;
When you're done manipulating the document, you'll probably want to get the HTML out:
string html = doc.Render();
That's all there is to it. There are a vast number of methods on the CQ object, covering all the jQuery DOM manipulation techniques. There are also utility methods for handling JSON, and it has extensive support for dynamic and anonymous types to make passing data structures (e.g. a set of CSS classes) as easy as possible -- much like jQuery.
Some More Advanced Stuff
I don't recommend doing this unless you are familiar with lower-level tinkering with asp.net's http workflow. There's nothing at all undoable but there will be a learning curve if you've never heard of an HttpHandler.
If you want to skip the WebForms engine altogether, you can create an IHttpHandler that automatically parses HTML files. This would definitely perform better than overlaying on a the ASPX engine -- who knows, maybe even faster than doing a similar amount of server-side processing with web controls. You can then then register your handler using web.config for specific extensions (like htm and html).
Yet another way to automatically intercept is with routing. You can use the MVC routing library in a webforms app with no trouble, here's one description of how to do this. Then you can create a route that matches whatever pattern you want (again, perhaps *.html) and pass handling off to a custom IHttpHandler or class. In this case, you're doing everything: you will need to look at the path, load the file from the file system, parse it with CsQuery, and stream the response.
Using either mechanism, you'll need a way to tell your project what code to run for each page, of course. That is, just because you've created a nifty HTML parser, how do you then tell it to run the correct "code behind" for that page?
MVC does this by just locating a controller with the name of "PageNameController.cs" and calling a method that matches the name of the parameter. You could do whatever you want; e.g. you could add an element:
<script type="controller" src="MyPageController"></script>
Your generic handler code could look for such an element, and then use reflection to locate the correct named class & method to call. This is pretty involved, and beyond the scope of this answer; but if you're looking to build a whole new framework or something this is how you would go about it.
Intercepting the content of the page prior to it being sent is rather simple. I did this a while back on a project that compressed content on the fly: http://optimizerprime.codeplex.com/ (It's ugly, but it did its job and you might be able to salvage some of the code). Anyway, what you want to do is the following:
1) Create a Stream object that saves the content of the page until Flush is called. For instance I used this in my compression project: http://optimizerprime.codeplex.com/SourceControl/changeset/view/83171#1795869 Like I said before, it's not pretty. But my point being you'll need to create your own Stream class that will do what you want (in this case give you the string output of the page, parse/modify the string, and then output it to the user).
2) Assign the page's filter object to it. (Page.Response.Filter) Note that you need to do it rather early on so you can catch all of the content. I did this with a HTTP Module that ran on the PreRequestHandlerExecute event. But if you did something like this:
protected override void OnPreInit(EventArgs e)
{
this.Response.Filter = new MyStream();
base.OnPreInit(e);
}
That would also most likely work.
3) You should be able to use something like Html Agility Pack to parse the HTML and modify it from there.
That to me seems like the easiest approach.
I have a tree view created using HTML and Jquery only.
I would like to know can i create a custom control using just HTML and jquery to make it re-usable. If yes then can someone please throw some light on how i can achieve this
Thanks in advance
In order to make it reusable as an ASP.NET control, it also has to be naming container safe, if you want to be sure it can be safely dropped anywhere, or used more than once on a page. This means you need to be sure that you are passing the script a reference to a unique ID of the root of the control's markup (e.g. the ClientID), and any other references are relative to that.
But generally, you can make a custom control self-contained in several ways. If it has no controls, then you could include all the resources (HTML and script) as embedded resources. The control can at the simplest level stream its own embedded resources to the client in the Render method.
To deal with scripts, you can similarly use ScriptManager to register it's own embedded javascript as a client script block. This is not ideal, though, because your script will always be included in a block, and therefore probably not cached very well by the clients.
A better way is to serve embedded resources using WebResource.axd. Here is an article that explains how to do this.
Personally, I find WebResource and embedded resources to be a huge pain in the neck. You need to keep AssemblyInfo.cs in sync with the resources, and assembly name & namespace conventions always seem to be impossibly difficult to get correct. I have found it much easier to simply expose a static method of the custom control, e.g.:
public static Stream GetEmbeddedResource(someResourceIdentifier, out string mimeType) {
/// return a stream of my own embedded resource ... can be used for anything
/// css, js, html
}
Then just create your own web handler to use as a resource loader and stream the contents. This is so much easier, and you also don't end up with WebResource.axd includes with 200 character long query strings.
I have a form in my content page for which I am doing some client side validations via Javascript. The Javascript behaves as expected if I place the JS code directly in the content page. But if I place the JS code in it's own file and try accessing that from the content/master page (through the script tag's src attribute), I get a run time error when the validation function in JS being called.
To be specific, I get the below error.
Microsoft JScript runtime error: Objected expected/required at this line - document.getElementById('<%=txtemailId.ClientID %>').value
txtemailId is in the content page.
Javascript code is placed in validation.js and accessed via master page.
The reason I guess is that when .net is parsing the files, it is unable to substitute txtemailId.ClientID with the client side value that would be generated later on. So, how should one go about it? Thanks!
The answer to this is quite simple.
Within your content page declare an in-line JScript variable, make sure this is above your tag.
<script>
var emailClientId = <%=txtemailId.ClientID%>;
</script>
Within your include.js file make use of the globally scoped emailClientId variable.
Obviously this is a bit clumsy because not all of the JScript code is contained within the include.js file, which makes it difficult to debug / diagnose as it is not clear specifically where the value is coming from. You should clearly comment / document this within your code to make maintenance of he codebase easier in the future.
You're right, the code <%=txtemailId.ClientID %> will only get replaced with the real client ID by ASP.Net if this code is in an ASP.Net file. So if you put this javascript in a separate .js file, ASP.Net will know nothing about it, and the code will not be parsed.
The easiest way to achieve this is to make the control IDs parameters of your functions. This way you can have the calling javascript code in your .aspx (or .ascx) file, along with the <%=txtemailId.ClientID %> code.
Standalone .js files are not run through the ASPX parser, so your expression is not being evaluated.
To solve the problem, you could set global variables (or function parameters, or something else) in the ASPX files with the IDs of the controls, then use them in the standalone .js file.
Alternatively, you could uses class names (which don't get mangled) instead of IDs. (This is very simple using jQuery)
An approach like this is best suited for something you want to achieve:
validation.js
var Validation = {
EmailId: null,
Validate: function() {
var email = document.getElementById(EmailId).value;
}
}
page.aspx
Validation.EmailId = '<%=txtemailId.ClientID %>'; //initialize
Validation.Validate(); //whenever you want to validate
I am trying to make use of the yahoo exceptional performance rule : avoiding duplicate script
To do so i would like to be able to know whether or not a script was already added to the page before injecting it in the page. It looks like i can't figure what has been added in asp.net code behind unless i have a scriptmanager added to the page. but i would like to avoid using asp.net AJAX. From the description of the rule, it looks like it is something possible in php though.
Assuming that i can't do the check in my code behind, i was considering using jQuery $.getString function but it doesn't check before fetching the script. If i was to choose the javascript file, would i have to parse the whole http response in order to figure out which script was loaded on the page?
If the page is registering the scripts with the ASP.NET Page.ClientScript Register APIs then you can use Page.ClientScript.IsClientScriptIncludeRegistered. On the other hand, if you are using those APIs you don't really need to call it, since it already ensures only one of each is registered.
http://msdn.microsoft.com/en/us/library/system.web.ui.clientscriptmanager.isclientscriptincluderegistered.aspx
If the page just has regular ole script elements statically in the markup, and you need to detect if a script is loaded on the client side, you will have to get all the script elements on the page and look at their .src values. The thing with that is that some browsers automatically resolve that url to a full path, not just the one you declared. So, you can account for that in various ways -- you can just search for the end of the string being the script you want, or you can cause the url you want to compare with to also be resolved by setting it onto a dynamically created script element (which you never add to the DOM but is still resolved for you).
This is just off the top of my head, sorry if I get something wrong:
var s = document.createElement("script");
s.src = "foo.js";
var loaded, scripts = document.getElementsByTagName("script");
for (var i = 0; i < scripts.length; i++) {
if (scripts[i].src === s.src) {
loaded = true;
break;
}
}
if (loaded) {
// this script is already loaded
// assuming you dont have multiple copies in different locations
}
You don't need to use any client-side scripting to do this... you can do this in your code behind using the ClientScriptManager without needing to make use of ASP.NET AJAX (I think you're confusing ClientScriptManager with ScriptManager*) in your control/page just use:
ClientScript.RegisterClientScriptInclude("some-script", "myScript.js");
or from your user controls:
Page.ClientScript.RegisterClientScriptInclude("some-script", "myScript.js");
This will use the key "some-script" & only register one copy of the script on the page.
*To be clear I think the confusion is arrising from the difference between these:
ClientScriptManager if a server-side helper class which is used to manage client side scripts (in other words its whole purpose is to do exactly what you are trying to do). It is accessed via the Page's ClientScript property.
ScriptManager is a Control used to aid client side Ajax scripting in ASP.NET AJAX
(hell I even confused myself & gave the wrong example code initially)
well that wouldn't actually work in a master detail scenario with multiple web user controls.
Then you wouldn't have control over who has to do the script initialization if the web user control is dynamic.
It's easier to link once, but a developer would have to weigh his options between ClientManager and using a script load.
yeah you have to parse the whole response...
why don't you create a javascript file and put all of your javascript there and then import that javascript file in your code??? in this way you can get rid of duplicate script insertion.
is there a way to find all script files added to a page in asp.net code behind? i am trying to add script dynamically but would like to check first if it already exist on the page.
AFAIK, no. Other developers can just add <script> tag on the fly and not through the .NET objects.
If you ensure that everyone uses ScriptManager, then you can use GetRegistered* methods on the object.
If it's inline script, you can use ClientScriptManager.RegisterClientScriptBlock which uniquely identifies a script by its type and key and will make sure it's registered only once.