<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Firefox3,IE6,IE7,IE8上传图片预览</title>
<style type="text/css">
#preview_wrapper{
display:inline-block;
150px;
height:150px;
background-color:#CCC;
}
#preview_fake{ /* 该对象用户在IE下显示预览图片 */
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale);
}
#preview_size_fake{ /* 该对象只用来在IE下获得图片的原始尺寸，无其它用途 */
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);
visibility:hidden;
}
#preview{ /* 该对象用户在FF下显示预览图片 */
150px;
height:150px;
}
</style>
<script type="text/javascript">
function onUploadImgChange(sender) {
if (!sender.value.match(/.jpg|.gif|.png|.bmp/i)) {
alert('图片格式无效！');
return false;
}
var objPreview = document.getElementById('preview');
var objPreviewFake = document.getElementById('preview_fake');
var objPreviewSizeFake = document.getElementById('preview_size_fake');
if (sender.files && sender.files[0]) {
objPreview.style.display = 'block';
objPreview.style.width = 'auto';
objPreview.style.height = 'auto';
// Firefox 因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
objPreview.src = window.URL.createObjectURL(sender.files[0]);
} else if (objPreviewFake.filters) {
// IE7,IE8 在设置本地图片地址为 img.src 时出现莫名其妙的后果
//（相同环境有时能显示，有时不显示），因此只能用滤镜来解决
// IE7, IE8因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
sender.select();
var imgSrc = document.selection.createRange().text;
objPreviewFake.filters.item(
'DXImageTransform.Microsoft.AlphaImageLoader').src = imgSrc;
objPreviewSizeFake.filters.item(
'DXImageTransform.Microsoft.AlphaImageLoader').src = imgSrc;
autoSizePreview(objPreviewFake,
objPreviewSizeFake.offsetWidth, objPreviewSizeFake.offsetHeight);
objPreview.style.display = 'none';
}
}
function onPreviewLoad(sender) {
autoSizePreview(sender, sender.offsetWidth, sender.offsetHeight);
}
function autoSizePreview(objPre, originalWidth, originalHeight) {
var zoomParam = clacImgZoomParam(150, 150, originalWidth, originalHeight);
objPre.style.width = zoomParam.width + 'px';
objPre.style.height = zoomParam.height + 'px';
objPre.style.marginTop = zoomParam.top + 'px';
objPre.style.marginLeft = zoomParam.left + 'px';
}
function clacImgZoomParam(maxWidth, maxHeight, width, height) {
var param = { width, height: height, top: 0, left: 0 };
if (width > maxWidth || height > maxHeight) {
rateWidth = width / maxWidth;
rateHeight = height / maxHeight;
if (rateWidth > rateHeight) {
param.width = maxWidth;
param.height = height / rateWidth;
} else {
param.width = width / rateHeight;
param.height = maxHeight;
}
}
param.left = (maxWidth - param.width) / 2;
param.top = (maxHeight - param.height) / 2;
return param;
}
</script>
</head>
<body>
<div id="preview_wrapper">
<div id="preview_fake">
<img id="preview" onload="onPreviewLoad(this)" width="240px" height="240px" src="a.png"/>
</div>
</div>
<br/>
<input id="upload" type="file" onchange="onUploadImgChange(this)"/>
<br/>
<img id="preview_size_fake"/>
</body>
</html>