webform 文件上传(头像上传) 隐藏FileUpload

 1         <div>
 2             <%-- 核心思想:把FileUpload设为relative,top:-200px;opacity:0 --%>
 3             <div id="localImag" style="width: 300px; height: 200px">
 4                 <img id="preview" alt="预览图片" src="images/qiye.png" width="300" height="200" />
 5                 <asp:FileUpload ID="PicLoad" Width="300px" Height="200px" Style="position: relative; top: -200px; opacity: 0" runat="server" onchange="javascript:setImagePreview(this,localImag,preview);"></asp:FileUpload>
 6 
 7             </div>
 8             <asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="上传" />
 9 
10             <script type="text/javascript">
11                 function setImagePreview(docObj, localImagId, imgObjPreview) {
12                     if (docObj.files && docObj.files[0]) {
13                         //火狐下，直接设img属性  
14                         imgObjPreview.style.display = ‘block‘;
15                         imgObjPreview.style.width = ‘300px‘;
16                         imgObjPreview.style.height = ‘200px‘;
17 
18 
19                         //火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式    
20                         imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
21                     }
22                     else {
23                         //IE下，使用滤镜  
24                         docObj.select();
25                         var imgSrc = document.selection.createRange().text;
26 
27                         //必须设置初始大小  
28                         localImagId.style.width = "300px";
29                         localImagId.style.height = "200px";
30 
31                         //图片异常的捕捉，防止用户修改后缀来伪造图片  
32                         try {
33                             localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
34                             localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
35                         }
36                         catch (e) {
37                             alert("您上传的图片格式不正确，请重新选择!");
38                             return false;
39                         }
40                         imgObjPreview.style.display = ‘none‘;
41                         document.selection.empty();
42                     }
43                     return true;
44                 }
45             </script>
46         </div>