I am having a rails app that basically changes replaces images at pre-decided time. Now i want to create a ruby timer that triggers an event every second and when any image time is reached, it throws the event and the image changes in the view. I was thinking of using observer pattern for this. Can anyone please advise me on how to go about doing this?
Any help is appreciated.
Have a look at gems that handle scheduled tasks for you. I've used Taskit quite successfully in the past.
http://ruby-toolbox.com/categories/scheduling.html
Sounds like you may also want image-rotating Javascript...
RubyOnRails is a server-side technology. It does not work in the way, which would let the rails application to change the 'view', after it has been rendered and sent to the client's browser.
You should use a JavaScript for this task.
You may decide who (client or the server) decides which image to serve. You may place all the URLs of the images in JavaScript, or you may provide a single resource in your rails application, which will return different images (or their URLs) in each request. There are many ways, but if I understood your question correctly, observers are not related to the problem.
Related
I’m looking for a neat way to execute a check to see if there are any messages in an inbox (realtime) in a Grails 2.x application.
I’ve moved away from polling via ajax to websockets, which is great at the point where someone actually sends you the message, but when you change to another screen, the “count” still needs to be initialized.
Can anyone advise on a elegant way of doing this?
Interceptors are not ideal as I need to check across just about all controllers
Filters are not ideal because on some screens with graphs there are many ajax request, the check would be run many times for each request.
I’m wondering if there are any other solutions that I’m not thinking of.. but possibly not.
A filter that disregards the check if a request header indicates an Ajax request would work.
Depending on where you need this "count" you could: In your layout (main.gsp for instance) call a tag library which makes use of a service to fetch the count. That way it's only applied to GSPs where the layout is applied (e.g. not any ajax request).
Not long ago I came across this website: http://www.danasoft.com/
This websites provides dynamically updating signatures which are pretty cool in my opinion.
There is just one thing that I don't get and would really like to know how to do.
Here's a direct link to an image on the website: http://www.danasoft.com/vipersig.jpg Try refreshing. Notice it changes? How do I achieve that? How do I have a direct link to a file like www.mypage.com/thing.jpeg output different images each time?
Basically, the URL is not actually retrieving the file directly each time, but rather the server is intercepting that URL and serving a (possibly random) image from a larger set of images. Depending on whether the server is running Apache, IIS, etc, the implementation could vary... This could also probably be achieved with the MVC routing engine by defining a custom route handler for URLs ending in '.jpg', but I'm not actually sure.
EDIT:
See this discussion for more detail on the MVC implementation.
I have a partial template that I want to intermittently poll the server (one of my controllers) and update its display with the result.
What is the appropriate way to do this with grails?
I have seen some articles saying there are specific grails tags for ajax calls, which would be nicer as it would allow clean direction to a controller/method, however, I've not seen anything in Grails to suggest that polling of a controller method could be done altogether.
Thanks!
There's nothing built into Grails that will do the polling for you. The most basic way is to simply use the setInterval() function in your JavaScript. If you're using a JavaScript library then something might be available there that would make things easier on you.
As a side note, be careful when implementing polling. If you're application isn't scaled correctly and you expect a lot of users, polling can bring your system down quickly.
I'm still pretty new to AJAX and javascript, but I'm getting there slowly.
I have a web-based application that relies heavily on mySQL and there are individual user accounts that are accessed and the UI is populated with user specific data.
I'm working on getting rid of a tabbed navigation bar that currently loads new pages because all that changes from page to page is information within one box.
The thing is that box needs to reload info from the database, etc.
I have had great help from users here showing that I need to call the database within the php page that ajax is calling.
OK-so pardon the lengthy intro-what I'm wondering is are there any specific limitations to what ajax can call that I need to know about? IE: someone mentioned that it's best not to call script files and that I should remove scripts from the php page that is being called and keep those in the 'parent' page. Any other things like this I need to keep in mind?
To clarify: I'm not looking to discuss the merits/drawbacks of the technology. I'm wondering about specific coding implementation that I need to be aware of (for example-I didn't until yesterday realize that if even if I had established a mySQL connection on the page, that I would need to re establish that connection in my called page as well...makes perfect sense now).
XMLHttpRequest which powers ajax has a number of limitations. I recommend brushing up on the same origin policy. This is a pivotal rule because it limits where AJAX calls can be made.
First, you can't have Javascript embedded in the HTTP response to an AJAX call. That's a security issue.
No mention of the dynamics of the database, but if the data to be displayed in tabs doesn't have to be real-time, why not cache it server-side?
I find that like any other protocol, Ajax works best in tightly controlled conditions. It wouldn't make much sense for updating nearly the whole page, unless you find that the user experience is improved with an on-page 'loader'. Without going into workarounds, disadvantages will include losing the browser back button / history, issues such as the one your friend mentioned, and also embedded resources and other rich content can suffer as well, and just having an extra layer of complexity to deal with in your app. Don't treat it as magic sauce for your app - make sure every use delivers specific results that benefit your client / audience.
IMHO, it's best to put your client side javascript in a separate page and then import it - neater container. one thing I've faced before is how to call xml back which contains code to run such as more javascript - it's worth checking if this is likely earlier on and avoiding, than having to look at evals.
Mildly interesting.
From http://en.wikipedia.org/wiki/AJAX, I get a fairly good grasp of what AJAX is. However, it looks like in order to learn it, I'd have to delve into multiple technologies at the same time to get any benefit out of it. So two questions:
What are resources that can help me understand/use AJAX?
What sort of website would benefit from AJAX?
If you aren't interested in the nitty gritty, you could use a higher-level library like JQuery or Prototype to create the underlying Javascript for you. The main benefit is a vastly more responsive user interface for web-based applications.
There are many libraries out there that can help you get benefit out of AJAX without learning about implementing callbacks, etc.
Are you using .NET? Look at http://ajax.asp.net. If you're not, then take a look at tools like qcodo for PHP, and learn about prototype.js, jquery, etc.
As far as websites that would benefit: Every web application ever. :) Anything you interact with by exchanging information, not just by clicking a link and reading an article.
Every website can benefit from AJAX, but in my opinion the biggest benefit to AJAX comes in data entry sections - forms basically. I have done entire sites where the front end - the part the user sees had almost no AJAX functionality in it. All the AJAX stuff was in the administration control panel for assisting in (correct!) data entry.
There is nothing worse than submitting a form and getting back an error, using AJAX you can pretty much prevent this for everything but file uploads.
I find it easiest to just stay away from all the frameworks and other helpers and just do basic Javascript. This not only lets you understand what's going on under the covers, it also lets you do it in the simplest way possible. There's really not much to it. User the JS XML DOM objects to create an xml document client side. Sent it to the server with XMLHTTPRequest, and then process the result, again using the JS XML DOM objects. Start with something simple. Just try sending one piece of information to the server, and getting a small piece of information back.
The Mozilla documentation is good. Sites that benefit from it the most are ones that behave almost like a desktop application and need high interactivity. You can usually improve usability on almost any site by using it, however.
Ajax should be thought of as a means to alter some content on a page without reloading the entire page.
So when do you need to do this? Really only when you have some user interactions or form information that you want to keep intact while you change some content on the page.