问题
Sorry for a lack of example on this one, but I figure it's easy enough to understand.
I have a fixed background on my site, which is currently implemented like this:
#background {
position: fixed;
top: 0;
bottom: 0;
left: 0;
right: 0;
background-color: #28305e;
background-image: url(../images/background.jpg);
background-size: cover;
-moz-background-size: cover;
background-position: center center;
z-index: -10;
}
<div id="background"></div>
This is great in all browsers so far except for mobile browsers where they hide the address bar upon scroll-down. When the address bar is hidden, the viewport expands vertically, and the background-image jarringly resizes itself. On this particular site it will be common for users to scroll up and down, and the effect is distracting.
Any ideas or strategies on working around this or implementing the background in a different way?
I could wrap the entire thing in a fixed container, and set the overflow-y to scroll, which prevents the address bar from ever being hidden, but I'd prefer not to do this (Google Glass can't scroll through those containers, haha... Would like to demo on there as well).
I've been trying to think of something that provides background-image: cover functionality with some sort of buffer, so that it renders larger than the viewport, and won't re-render unless the viewport is expanded beyond that buffer, but I'm not sure how to implement that.
EDIT: I actually did implement this and detailed the process in an answer below. However, even with this buffer setup (which extends the height of the background image to be 60+ pixels larger than the viewport height), upon the address bar hiding, it still shows a blank background-color segment that gets revealed, and once you stop scrolling, it renders the rest of the background image.
Still looking for a way to keep the native address bar hide functionality (which has now been expanded to iOS Safari on iPad in iOS 8), and also have a fullscreen background image that always fully renders even if the viewport changes height when hiding the address bar. Starting to wonder if I should just be filing bug reports for all the browsers...
回答1:
I ended up creating a workaround for mobile. It may not degrade gracefully, but it's working well for the time being.
window.mobilecheck = function() {
var check = false;
(function(a){if(/(android|bb\d+|meego).+mobile|android|ipad|playbook|silk|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows (ce|phone)|xda|xiino/i.test(a)||/1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(a.substr(0,4)))check = true})(navigator.userAgent||navigator.vendor||window.opera);
return check;
}
if (window.mobilecheck() == true) {
var newHeight = $(window).height() + 70;
$("#background").css("height", newHeight);
}
I found that mobilecheck function on the internet ( http://detectmobilebrowsers.com/ ). If it returns true, I take my fixed background image container and add 70 to its height. Then when you drag the screen up and the web browser's address bar auto-hides (thus increasing the window height), it has enough extra height such that background-size: cover does not have to jarringly resize the background image to fit the screen again.
I could have just put the entire page into a fixed container and prevented mobile address bars from ever hiding, but I don't like sidestepping an otherwise neat feature of mobile browsers, and I know iOS isn't exactly thrilled with fixed containers that have their own scrollbars (there are workarounds of course, but I'd prefer my content to be in a more standard container).
EDIT: However, this workaround introduces this issue: CSS CHALLANGE: Background-Image with 100% height - White Space when Scrolling Mobile
回答2:
For mobile safari you must, unintuitively, attach fixed backgrounds to the html element like so.
html {
background: url(../img/bg.jpg) no-repeat center center fixed;
background-size: cover;
height: 100%;
overflow: hidden;
}
Then set the scrolling to the body.
body {
height: 100%;
overflow: scroll;
}
You'll still need the background div for IE 8 since it doesn't support the background-size property, so mobile browsers should hide it. The cleanest way to do this is to exploit IE 8's inability to read a media query
@media only screen { #background { display: none; }}
回答3:
For those still looking around for an answer, you can use the new vw and vh attributes with an element that is position: fixed.
This scrolls while the address bar moves/shrinks/etc., then remains fixed on the page.
#bgimg {
display: block;
background: no-repeat url(bg.png);
position: fixed;
top: 0;
left: 0;
width: 100vw;
height: 120vh;
}
回答4:
Its hard to say without an example but you may be missing width:100% that should stop any resizing with the scroll bar.
Another way to implement a fixed background on mobile is to have a background div with position: absolute and overflow: hidden and all your other background implementations, Then have a content div with overflow-y:scroll; and set the height of the content div using jquery or any other method you choose to get the window height with.
Check out this JS Fiddle for an example.
回答5:
I made this. I found that if you never really scroll the body/window you never trigger the autohide for Chrome. So wrap the content in a bigger div and just scroll that and the autohide never triggers. BUT ALSO!!! The autohide never triggers. (Address bar is always there). Wouldn't doubt for second you could hide the address bar after this but then how does the user get the address bar back?
html, body {
height: 100%;
overflow: hidden;
}
body {
height: 100%;
}
#background {
position: fixed;
left: 50%;
bottom: 0px;
min-width: 100%;
min-height: 120%;
z-index: 0;
background: url('background.gif');
margin-left: -50%;
background-position: center center;
background-attachment: fixed;
background-size: cover;
}
#main_container {
width: inherit;
height: inherit;
overflow-y: scroll;
}
.block {
position: relative;
text-align: center;
background: transparent;
height: 100%;
z-index: 9;
}
.block {
width: 100%;
height: 100%;
background: rgba(224, 224, 224, 0.4);
}
.block::before {
content: '';
display: inline-block;
height: 100%;
vertical-align: middle;
}
.centered {
display: inline-block;
vertical-align: middle;
}
<div id="main_container">
<div class="block" >
<div class="centered">
<h1 class="circle">Some text</h1>
</div>
</div>
<div class="block">
<div class="centered">
<h1>Some text</h1>
</div>
</div>
<div class="block">
<div class="centered">
<h1>Some text</h1>
</div>
</div>
<div class="block">
<div class="centered">
<h1>Some text</h1>
</div>
</div>
<div class="block" >
<div class="centered">
<h1>Some text</h1>
</div>
</div>
</div>
<div id="bg"></div>
回答6:
Almost 5 years later, there is finally a fix for this, due to changes in how Safari and now Chrome for Android calculate vh units. Check it out! https://developers.google.com/web/updates/2016/12/url-bar-resizing
I implemented it on this website (can't really show this off on any of the code playgrounds due to them always embedding results in iframes): https://www.cochranesupply.com
Just used the following code on a background element:
#background {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100vh;
background-image: url(../images/background.jpg);
background-size: cover;
z-index: -1;
}
And that's all there is to it! Just need Chrome for Android 56, or Safari for iOS (not certain which version but this may have been in Safari for a long time now).
来源：https://stackoverflow.com/questions/23299960/prevent-fixed-position-background-image-cover-from-resizing-in-mobile-browsers