上传图片预览-兼容IE6，IE7，IE8，FF
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
?<meta http-equiv=Content-Type content="text/html; charset=utf-8"/>
?<meta http-equiv=X-UA-Compatible content=IE=EmulateIE7/>
??? <title>Firefox3,IE6,IE7,IE8上传图片预览</title>
??? <style type="text/css">
??????? #preview_wrapper
??????? {
??????????? display: inline-block;
??????????? width: 300px;
??????????? height: 300px;
??????????? 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 */
??????????? width: 300px;
??????????? height: 300px;
??????? }
??? </style>
??? <script type="text/javascript">
??????? function onUploadImgChange(sender)
??????? {
??????????? if (!sender.value.match(/.jpg|.gif|.png|.bmp/i)) //忽略大小写
??????????? {
??????????????? 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 = sender.files[0].getAsDataURL();
??????????? }
??????????? 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(300, 300, 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: 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)" />
??????? </div>
??? </div>
??? <br />
??? <input id="upload_img" type="file" onchange="onUploadImgChange(this)" />
??? <br />
??? <img id="preview_size_fake" />
</body>
</html>
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