Preloading images for rollover buttons (C#)

Posted on 2006-11-12
Last Modified: 2012-06-27
Hi All!

I have a webpage with some rollover graphics that are quite large.  I would like them to preload as soon as the page does, rather than waiting for the user to put their mouse over them.  To be honest, I'm running it locally so it's hard to tell whether it's doing it or not - but my understanding is you need some javascript or similar to get them to preload, and it will be deployed to the web soon enough.

Can I do it in C# in the Page_Load section, or do I need Javascript?  Either way, what code would I use?

Many thanks everyone!
Question by:glinkot
  • 3
  • 2

Accepted Solution

ryandale56 earned 250 total points
Comment Utility

Author Comment

Comment Utility
Hi Ryan,

Many thanks.  I did do some googling and saw similar type of stuff - is there always a necessity to specify the image size for these scripts?  Manually finding out the size of every image is kind of acceptable, but not the ideal for a long term effort.

LVL 12

Expert Comment

Comment Utility
>> "is there always a necessity to specify the image size for these scripts"
I've never used them, just leave the prams empty ()

>> "I'm running it locally so it's hard to tell whether it's doing it or not "
Go to google, and search for a larger image, and use that just for development testing.
Maximize Your Threat Intelligence Reporting

Reporting is one of the most important and least talked about aspects of a world-class threat intelligence program. Here’s how to do it right.


Author Comment

Comment Utility
Aha!  Are there any requirements around naming the pic versus the servertag name-ie do they need to be the same name, or do they need to differ for some reason?  I assume it just caches via the filename and when the servertag sees that it needs that path and filename, it picks it up from the cache rather than the webserver.

Am I right do you think?

Many thanks
LVL 12

Assisted Solution

UnexplainedWays earned 250 total points
Comment Utility
>> "Are there any requirements around naming the pic versus the servertag name-ie do they need to be the same name"

VARIABLE = new Image();

the variable and filename can be anything, and the name/id of the <img> or <asp:Image> makes no difference.  The only reason it would matter is when you want to assign the new filename to the image, cause without the id/name you can't find it.

Also, you can keep the VARIABLE  global, so say you have

imgOn = new Image();
imgOff = new Image();

imgOn.src = 'on.gif';
imgOff.src = 'off.gif';

and then in your code, you change the src of the image alot (and in different places), you can keep the filename down to one place (above) and use that when assigning the new image, example:

document.getElementById("TheImageId").src = imgOn.src;

And about the cashing, as far as i know, if you do this:

imgOn = new Image();
imgOn.src = 'on.gif';
---then later---
document.getElementById("TheImageId").src = 'on.gif';

This will look in the temp inet files first for the image, if it's there walla, if not u know what it does.  So it's not really about what the javascript does, its about if the file matches the name.


Author Comment

Comment Utility
Thankyou so much for your help guys!  Really appreciate your efforts.

Featured Post

Free Trending Threat Insights Every Day

Enhance your security with threat intelligence from the web. Get trending threat insights on hackers, exploits, and suspicious IP addresses delivered to your inbox with our free Cyber Daily.

Join & Write a Comment

I recently went through the process of creating a Calendar Control of events with the basis of using a database to keep track of the dates that are selectable, one requirement was to have the selected date pop-up in a simple lightbox.  At first this…
It was really hard time for me to get the understanding of Delegates in C#. I went through many websites and articles but I found them very clumsy. After going through those sites, I noted down the points in a easy way so here I am sharing that unde…
In this tutorial you'll learn about bandwidth monitoring with flows and packet sniffing with our network monitoring solution PRTG Network Monitor ( If you're interested in additional methods for monitoring bandwidt…
This demo shows you how to set up the containerized NetScaler CPX with NetScaler Management and Analytics System in a non-routable Mesos/Marathon environment for use with Micro-Services applications.

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now