上傳圖片預覽-相容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上傳圖片預覽</title>
<style type="text/css">
#preview_wrapper
{
display: inline-block;
width: 300px;
height: 300px;
background-color: #CCC;
}
#preview_fake
{
/* 該物件使用者在IE下顯示預覽圖片 */
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale);
}
#preview_size_fake
{
/* 該物件只用來在IE下獲得圖片的原始尺寸，無其它用途 */
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);
visibility: hidden;
}
#preview
{
/* 該物件使用者在FF下顯示預覽圖片 */
width: 300px;
height: 300px;
}
</style>
<script type="text/javascript">
function onUploadImgChange(sender)
{
if (!sender.value.match(/.jpg|.gif|.png|.bmp/i)) //忽略大小寫
{
alert('圖片格式無效！');
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 因安全性問題已無法直接通過 input[file].value 獲取完整的檔案路徑
objPreview.src = sender.files[0].getAsDataURL();
}
else if (objPreviewFake.filters)
{
// IE7,IE8 在設定本地圖片地址為 img.src 時出現莫名其妙的後果
//（相同環境有時能顯示，有時不顯示），因此只能用濾鏡來解決
// IE7, IE8因安全性問題已無法直接通過 input[file].value 獲取完整的檔案路徑
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>