jCrop (jQuery) sometimes fails to load image/cropper area

Question

I've got a pretty simple problem, but I've become clueless on what is causing the problem. In one of my applications I'm using jCrop as a small add-on to crop images to fit in banners/headers etc. These steps will be taken:

1) Select an image (using CKFinder for this, CKFinder returns the image path to an input field)
2) Click a button to load the image
3) Crop the image
4) Save the image

in about 75% of the cases everything goes according to plan, however the in the other 25% of the cases jCrop fails to load the cropping area and leaves it blank. Here's the jQuery code I'm using:

jQuery('#selectimg').live('click', function(e) { 
  e.preventDefault();
  var newsrc = jQuery('#img2').val();
  jQuery('#cropbox').attr('src', newsrc);
  var jcrop_api = jQuery.Jcrop('#cropbox', {
    boxWidth: 700, 
    boxHeight: 700,
    onSelect: updateCoords,
    onChange: updateCoords
  });
  //Some other JS code come's here for buttons (they work all the time)
});

I noticed that when I left the part away where #cropbox is being transformd in a cropable area, that the image is loading just fine, so the mistake lies with the var = jcrop_api part, but I slowsly start to think that there is no solution for this...

This is what I've tried so far:

Making a div <div id="cropper-box"></div> and use jQuery('#cropper-box').append('<img src="" id="cropbox" />'); and afterwards set the value. I tried the same thing but setting the image src in 1 step instead of afterwards.

I tried to put a placeholder on the page <img src="placeholder.png" id="cropbox" /> and change the source upon clicking the button. This works, but the cropperarea stays the size of the image (300x180px or something) and doesn't get bigger as it should.

// Edit:

Trying some more showed me that the image source is being replaced properly(! using Firefox to show the source for the selected text), I double checked the URL but this was a correct URL and a working image.

At the place where the cropper should be, there's an about 10x10 pixel white spot where the cropper icon (a plus sign) is popping up.. but as said before: the image isn't shown.

// Edit 2:

So I've took the sources for both the 1st and the 2nd try for the same image. As told before the first try the image won't load properly and the 2nd try it does (only when the 2nd try is the same image(!!)).

The selected page source shows 1 difference which is, first try:

<img style="position: absolute; width: 0px; height: 0px;" src="http://95.142.175.17/uploads/files/Desert.jpg">

second try:

<img style="position: absolute; width: 700px; height: 525px;" src="http://95.142.175.17/uploads/files/Desert.jpg">

I guess this is the image that's being replace by jCrop, but it's a complete riddle why it puts 0 heigth/width in there the first and the proper sizes the second time.

Answer 1

Okay guys, in case anyone else runs into this problem:

jCrop kinda gets messed up if the actions of loading an image and applying jCrop to it are queued too fast after eachother. I still find it strange that a second attempt works perfect, but I think that has something to do with cached image dimensions which are recognized by the DOM of the page or something.

The solution I came up with was by creating a function that converts the #cropbox into a jCrop area and then setting a 2 second interval, just to give jCrop some time to recognize the image and it's dimensions and then convert the element.

This is the part of html I used (with a preloader):

<div id="cropper-loading" style="display: none;"><img src="images/analytics/ajax-loader.gif" /></div>
<img id="cropbox" src="images/placeholder.png" style="display: none;" />

As you can see both the cropbox image and cropper-loading div are hidden as they are not needed instantly. You could display the placeholder if you wanted though.. Then this HTML form is used:

<input name="image2" id="img2" type="text" readonly="readonly" onclick="openKCFinder(this)" value="click here to select an image" style="width: 285px;" />  <button class="button button-blue" type="submit" name="load" id="selectimg">Load Image in cropper</button>

In my case I've been using KCFinder to load the images (it's part of CKEditor, really worth watching into!), KCFinder handles uploads, renaming etc and after choosing it returns the chosen image path (relative/absolute is configurable) to the input field.

Then when clicking #selectimg this code is called:

jQuery('#selectimg').click(function(e) { 
    e.preventDefault();
    jQuery('#cropper-loading').css('display', 'block');

    var newsrc = jQuery('#img2').val();

    jQuery('#cropbox').attr('src', newsrc);
    jQuery('#img').val(newsrc);

    function createJcropArea() {
        jQuery('#cropper-loading').css('display', 'none');                                      
        jQuery('#cropbox').css('display', 'block');
        var jcrop_api = jQuery.Jcrop('#cropbox', {
            boxWidth: 700, 
            boxHeight: 700,
            onSelect: updateCoords,
            onChange: updateCoords
        });
        clearInterval(interval);
    }
    var interval = setInterval(createJcropArea, 2000);
});

At first I prevent the link too be followed as it normally would (or button action) and after that the loading div is displayed (that's my reason for hiding the placeholder image, otherwise it would look messed up).

Then the image location is being loaded from the input field and copied into another (#img), this field is used to process the image afterwards (PHP uses the value of #img to load this image). Also simultaneously the #cropbox src is being set to the new image.

And here comes the part which solved my problem:

Instead of directly activating jCrop, I've made a function that:

1) hides the loading icon
2) displays the image
3) converts #cropbox into a jCrop area
4) clean the interval (otherwise it would loop un-ending)

And after this function you can see that, just to be save, I took 2 seconds delay before the jCrop area is being converted.

Hope it helps anyone in the future!

Cheers and thanks for thinking @vector and whoever else did ;-)

Answer 2

Creating an 'Image' object and setting up the 'src' attribute does not apply that you can treat the image like it had already been loaded. Also, giving any fixed timeout interval does not guaranty the image has already been loaded.

Instead, you should set up an 'onload' callback for the Image Object - which will then initialize the Jcrop Object:

var src = 'https://example.com/imgs/someimgtocrop.jpg'; 
var tmpImg = new Image();
tmpImg.onload = function() {
   //This is where you can safely create an image and a Jcrop Object
};
tmpImg.src = src; //Note that the 'src' attribute is only added to the Image Object after the 'onload' listener was defined