How to preload images with PhoneGap? - css

Question

I've come to believe that there's two things happening. Firstly, if you want to preload a url, you can do this:
body:after{
content: url(http://www.example.com/img/img_1.png) display:none;
}
But as far as I know, this doesn't help in this case:
body:after{
content: url(../img/img_1.png) display:none;
}
In this latter case, the image is already local, so it doesn't have to "download" it? Is that true? Or will the first bit of code cache the image even more?
I ask, because even though I do this, and I then transition to another page, using jquery mobile, the next page still takes a few seconds to load the background image. Even though it's a local asset.
How do I get around this?

Answer 1

From the tests I've done, it seems that two things can cause a delay when loading an image:
When the image needs to be loaded from a URL, or
When the image is locally located, but needs to be placed on the display screen
What i didn't realise is that with PhoneGap, even with the images local, it might take a little while to load. This is what was causing issues for me. Well, this and the fact that I was loading from URLs. So in my case I used the "CSS3 Caching Plugin" like so:
jQuery(function($) {
$.preload.images(document)
});
This solved my problem of loading images that was in the CSS file. But then for my own convenience, I added a section to the css file for locally cached files. Like so:
#cacheMe1 { background: #ffffff url('../img/img1.png') 50% 50% repeat-x; }
#cacheMe2 { background: #ffffff url('../img/img2.png') 50% 50% repeat-x; }
#cacheMe3 { background: #ffffff url('../img/img3.png') 50% 50% repeat-x; }
#cacheMe4 { background: #ffffff url('../img/img4.png') 50% 50% repeat-x; }
etc
This solved caching for most images, plus it allowed me to still keep URLs as loading in the app (i have a gallery section where its currently acceptable to see the images load, rather than on display).
What I also did that seems to be working, is that I use the "InAppBrowser" plugin to preload entire pages by opening them in a hidden window:
var ref = window.open('http://www.example.com', '_blank', 'hidden=yes');
If you open a bunch of files on load of the app, it seems when you either open these URLs again, or switch to the window with:
ref.show();
So there's two decent ways I've found to cache files that works perfectly for my scenario. Hope it helps someone else!

Answer 2

I do not know if I understood well, but maybe it can useful for you:
<img src="my.png" onerror="this.src = 'image-not-found.png';" />

Answer 3

When I was facing problems with preloading images I had to abandon an idea of using display:none; cause it didn't work properly (as long as I remember the browser refuses to load content of invisible elements in order to speed page load up and reducing the traffic). Instead I created a div that in browser's opinion was visible, but it had zero width and height. Required images I load as background-image for this block. The whole trick is that background-image property can take multiple values. The CSS will look like this:
#preload {
height: 0;
width: 0;
background-image: url(image-1.png), url(image-2.png);
}
So you don't get mess in the markup. Hope this trick will work in your case.

Answer 4

You don't need to attach the image to the DOM directly, therefor there is no need to use css to hide it. Use JavaScript to preload images.
var image = new Image();
image.src = "yourfile.jpg"
you can then provide a longer term solution using appcache.