问题
This code is supposed to reposition gallery images inside of their square div boxes. All the images have a set height e.g. 100px. But their widths are different. Rather than only show the left-most 100px of every picture, I'd rather it show the center.
All I need is to go through each img and change the left property to shift the images left.
$('img.gall_imgs').load(function() {
var $imgWidth = parseInt($(this).width); // "$(this)" or "this"? parseInt() needed?
var $divWidth = parseInt($(this).closest('div').width);
if($imgWidth > $divWidth) { // if img is wider than its containing div, we'll shift it left
var $position = -1 * ($imgWidth/2 - $divWidth/2); // will give decimals?
$position = parseInt($position) + "px"; // make $position format "123px". parseInt() needed here?
// var $position = '-50px'; // tested with pre-set position
this.css("left", $position); // "$(this)" or "this"?
}
//}
});
Also, I don't even know how to test variables values inside of jquery. I tried putting in an alert($imgWidth) but it obviously didn't work.
EDIT: Here is the CSS and HTML I have now:
.gall_thumb_img { // the div surrounding the img
width:200px;
height:200px;
margin-left:auto;
margin-right:auto;
overflow:hidden;
text-align:center; // just added this per suggestions. No effect
}
.gall_thumb_img img{ // the img
position:absolute;
display:block;
height:200px;
min-width:200px;
}
HTML:
<div id="gall_box">
<div class="gall_thumb_box" id="gall_thumb_box_0" >
<div class="gall_thumb_img" id="gall_thumb_img_0" >
<a href="?c=ecards&v=single&idx=23&img_dir=nature">
<img class="gall_img" id="img0" src="http://example.com/small.jpg?20111211044810"></a>
</div>
</div>
</div>
EDIT2: Here is what I've changed the jquery to based on various suggestions. Still no change in end result.
$(window).load(function() {
$('img.gall_imgs').each(function() {
var imgWidth = $(this).width(); // "$(this)" or "this"?
var divWidth = $(this).closest('div').width();
alert(imgWidth);
if(imgWidth > divWidth) {
var position = -1 * (imgWidth/2 - divWidth/2); // will give decimals?
position = position + "px"; // make position format "123px".
// var position = '-50px'; // tested with set position
this.css("left", position); // "$(this)" or "this"?
}
});
});
Text-align center is a good idea that I will use if I can get it to work, but I would still like to know why my jquery code is not working. Thank you.
回答1:
Something like this
$('img.gall_imgs').each(function() {
var $imgWidth = parseInt($(this).width());
var $divWidth = parseInt($(this).closest('div').width());
回答2:
You can use the jQuery $.each function to go over all img tags and modify them.
You could also use a div with a background-image and background-position of 'top center' ? I think it would work as well for you with showing the "center" part of the image.
By the way, why are you using the $ sign in your vars?
回答3:
You need to .append the <img /> first, then try to get/set it's properties.
As stated in the comments below, If they are already on your page, you don't need to listen on the onload event. You should use jQuery.each to iterate through them.
Like so:
$(function(){
$('img.gall_imgs').each(function() {
var that = $(this);
var $imgWidth = that.width();
var $divWidth = that.parent().width();
if($imgWidth > $divWidth) {
var $position = -1 * ($imgWidth/2 - $divWidth/2);
$position = $position.toString() + "px";
that.css("left", $position);
}
});
});
回答4:
You don't needed intParse and width is a jQuery function so you must write 'width()':
$('img.gall_imgs').load(function() {
var $imgWidth = $(this).width();
var $divWidth = $(this).closest('div').width();
if($imgWidth > $divWidth) {
var $position = Math.round(-1 * ($imgWidth - $divWidth) ) + "px";
$(this).css("left", $position);
}
});
A different (and better) option is to use the css attribute "text-align: center;". Inside the divs the images are inside so it works because the images displays inline into its container.
P.D.- "alert($imgWidth);" must show you its value, otherwise the execution is not reaching this line of code.
回答5:
The other answers on here had some clues, but they hardly changed the code I supplied and none of them worked. So I am going to answer my own question and post what worked.
This function will center images horizontally inside a div that has fixed width with overflow set to hidden, and it activates upon image load. Without this function, only the left N pixels, where N is the width of the containing div, would be visible. With this function, the center N pixels are visible instead.
$(window).load(function() {
$("img.gall_img").each(function() {
var imgWidth = $(this).width(); // use "$(this)" b/c "width()" is jquery
var divWidth = $(this).closest('div').width();
//alert(imgWidth + " and " + divWidth);
if(imgWidth > divWidth) {
var position = Math.round(-1 * ((imgWidth/2) - (divWidth/2))); // round up to next integer
position = position + "px"; // make position format "123px". parseInt() needed here?
$(this).css("left", position); // use "$(this)" b/c "css()" is a jquery function (otherwise, could use "this")
}
});
});
Things I learned.
- "$(document).ready" does not work here. Must use "$(window).load" because the ready function triggers before images are loaded. To manipulate image position and size, you have to wait till they are fully loaded.
- $(this) = this, except that you use $(this) when you want to access jQuery functions (like width() and css()) and properties.
- $("tag").each: loops through the collection of tags (or other objects) specified, applying the code within "each()" to each member of the collection in turn. Use "this" or "$(this)" inside to refer to the current member.
- It's hard to debug jQuery using Google Chrome.
来源：https://stackoverflow.com/questions/8463878/trying-to-set-css-property-left-to-using-jquery-centering-image-inside-div