问题
As you can see in the CSS below, I want child2 to position itself before child1. This is because the site I\'m currently developing should also work on mobile devices, on which the child2 should be at the bottom, as it contains the navigation which I want below the content on the mobile devices. - Why not 2 masterpages? This is the only 2 divs which are repositioned in the entire HTML, so 2 masterpages for this minor change is an overkill.
HTML:
<div id=\"parent\">
<div class=\"child1\"></div>
<div class=\"child2\"></div>
</div>
CSS:
parent { position: relative; width: 100%; }
child1 { width: auto; margin-left: 160px; }
child2 { width: 145px; position: absolute; top: 0px; bottom: 0px; }
child2 has dynamic height, as different subsites could have more or less navigation items.
I know that absolute positioned elements are removed from the flow, thus ignored by other elements.
I tried setting overflow:hidden; on the parent div, but that didn\'t help, neither does the clearfix.
My last resort will be JavaScript to reposition the two divs accordingly, but for now I\'ll try and see if there exist a non-JavaScript way of doing this.
回答1:
You answered the question by yourself: "I know that absolute positioned elements are removed from the flow, thus ignored by other elements." So you can't set the parents height according to an absolutely positioned element.
You either use fixed heights or you need to involve JS.
回答2:
Although stretching to elements with position: absolute is not possible, there are often solutions where you can avoid the absolute positioning while obtaining the same effect. Look at this fiddle that solves the problem in your particular case http://jsfiddle.net/gS9q7/
The trick is to reverse element order by floating both elements, the first to the right, the second to the left, so the second appears first.
.child1 {
width: calc(100% - 160px);
float: right;
}
.child2 {
width: 145px;
float: left;
}
Finally, add a clearfix to the parent and you're done (see the fiddle for the complete solution).
Generally, as long as the element with absolute position is positioned at the top of the parent element, chances are good that you find a workaround by floating the element.
回答3:
Feeela is right but you can get a parent div contracting/expanding to a child element if you reverse your div positioning like this:
.parent{
postion: absolute;
/* position it in the browser using the `left`, `top` and `margin`
attributes */
}
.child{
position: relative;
height: 100%;
width: 100%;
overflow: hidden;
/* to pad or move it around using `left` and `top` inside the parent */
}
This should work for you.
回答4:
There is a quite simple way to solve this.
You just have to duplicate the content of child1 and child2 in relative divs with display:none in parent div. Say child1_1 and child2_2. Put child2_2 on top and child1_1 at the bottom.
When your jquery (or whatever) calls the absolute div, just set the according relative div (child1_1 or child2_2) with display:block AND visibility:hidden. The relative child will still be invisible but will make parent's div higher.
回答5:
I had a similar problem. To solve this (instead of calculate the iframe's height using the body, document or window) I created a div that wraps the whole page content (a div with an id="page" for example) and then I used its height.
回答6:
There's a very simple hack that fixes this issue
Here's a codesandbox that illustrates the solution: https://codesandbox.io/s/00w06z1n5l
HTML
<div id="parent">
<div class="hack">
<div class="child">
</div>
</div>
</div>
CSS
.parent { position: relative; width: 100%; }
.hack { position: absolute; left:0; right:0; top:0;}
.child { position: absolute; left: 0; right: 0; bottom:0; }
you can play with the positioning of the hack div to affect where the child positions itself.
Here's a snippet:
html {
font-family: sans-serif;
text-align: center;
}
.container {
border: 2px solid gray;
height: 400px;
display: flex;
flex-direction: column;
}
.stuff-the-middle {
background: papayawhip
url("https://camo.githubusercontent.com/6609e7239d46222bbcbd846155351a8ce06eb11f/687474703a2f2f692e696d6775722e636f6d2f4e577a764a6d6d2e706e67");
flex: 1;
}
.parent {
background: palevioletred;
position: relative;
}
.hack {
position: absolute;
left: 0;
top:0;
right: 0;
}
.child {
height: 40px;
background: rgba(0, 0, 0, 0.5);
position: absolute;
bottom: 0;
left: 0;
right: 0;
} <div class="container">
<div class="stuff-the-middle">
I have stuff annoyingly in th emiddle
</div>
<div class="parent">
<div class="hack">
<div class="child">
I'm inside of my parent but absolutely on top
</div>
</div>
I'm the parent
<br /> You can modify my height
<br /> and my child is always on top
<br /> absolutely on top
<br /> try removing this text
</div>
</div>回答7:
With pure JavaScript, you just need to retrieve the height of your static position child element .child1 using the getComputedStyle() method then set that retrieve value as the padding-top for that same child using the HTMLElement.style property.
Check and run the following Code Snippet for a practical example of what I described above:
/* JavaScript */
var child1 = document.querySelector(".child1");
var parent = document.getElementById("parent");
var childHeight = parseInt(window.getComputedStyle(child1).height) + "px";
child1.style.paddingTop = childHeight;/* CSS */
#parent { position: relative; width: 100%; }
.child1 { width: auto; }
.child2 { width: 145px; position: absolute; top: 0px; bottom: 0px; }
html, body { width: 100%;height: 100%; margin: 0; padding: 0; }<!-- HTML -->
<div id="parent">
<div class="child1">STATIC</div>
<div class="child2">ABSOLUTE</div>
</div>回答8:
I came up with another solution, which I don't love but gets the job done.
Basically duplicate the child elements in such a way that the duplicates are not visible.
<div id="parent">
<div class="width-calc">
<div class="child1"></div>
<div class="child2"></div>
</div>
<div class="child1"></div>
<div class="child2"></div>
</div>
CSS:
.width-calc {
height: 0;
overflow: hidden;
}
If those child elements contain little markup, then the impact will be small.
回答9:
"You either use fixed heights or you need to involve JS."
Here is the JS example:
---------- jQuery JS example--------------------
function findEnvelopSizeOfAbsolutelyPositionedChildren(containerSelector){
var maxX = $(containerSelector).width(), maxY = $(containerSelector).height();
$(containerSelector).children().each(function (i){
if (maxX < parseInt($(this).css('left')) + $(this).width()){
maxX = parseInt($(this).css('left')) + $(this).width();
}
if (maxY < parseInt($(this).css('top')) + $(this).height()){
maxY = parseInt($(this).css('top')) + $(this).height();
}
});
return {
'width': maxX,
'height': maxY
}
}
var specBodySize = findEnvelopSizeOfAbsolutelyPositionedSubDivs("#SpecBody");
$("#SpecBody").width(specBodySize.width);
$("#SpecBody").height(specBodySize.height);
回答10:
There is a better way to do this now. You can use the bottom property.
.my-element {
position: absolute;
bottom: 30px;
}
回答11:
This is very similar to what @ChrisC suggested. It is not using an absolute positioned element, but a relative one. Maybe could work for you
<div class="container">
<div class="my-child"></div>
</div>
And your css like this:
.container{
background-color: red;
position: relative;
border: 1px solid black;
width: 100%;
}
.my-child{
position: relative;
top: 0;
left: 100%;
height: 100px;
width: 100px;
margin-left: -100px;
background-color: blue;
}
https://jsfiddle.net/royriojas/dndjwa6t/
回答12:
Also consider next approach:
CSS:
.parent {
height: 100%;
}
.parent:after {
content: '';
display: block;
}
Also since you are trying to reposition divs consider css grid
回答13:
This question was asked in 2012 before flexbox. The correct way to solve this problem using modern CSS is with a media query and a flex column reversal for mobile devices. No absolute positioning is needed.
https://jsfiddle.net/tnhsaesop/vjftq198/3/
HTML:
<div class="parent">
<div style="background-color:lightgrey;">
<p>
I stay on top on desktop and I'm on bottom on mobile
</p>
</div>
<div style="background-color:grey;">
<p>
I stay on bottom on desktop and I'm on bottom on mobile
</p>
</div>
</div>
CSS:
.parent {
display: flex;
flex-direction: column;
}
@media (max-width: 768px) {
.parent {
flex-direction: column-reverse;
}
}
回答14:
Absolute views position themselves against the nearest ancestor that isn't statically positioned (position: static), therefore if you want an absolute view positioned against a given parent, set the parent position to relative and the child to position to absolute
回答15:
Try this, it was worked for me
.child {
width: 100%;
position: absolute;
top: 0px;
bottom: 0px;
z-index: 1;
}
It will set child height to parent height
来源：https://stackoverflow.com/questions/12070759/make-absolute-positioned-div-expand-parent-div-height