webform 文件上传(头像上传) 隐藏FileUpload

         <div>
             <%-- 核心思想:把FileUpload设为relative,top:-200px;opacity: --%>
             <div id="localImag" style="width: 300px; height: 200px">
                 <img id=" />
                 <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>

             </div>
             <asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="上传" />

             <script type="text/javascript">
                 function setImagePreview(docObj, localImagId, imgObjPreview) {
                     ]) {
                         //火狐下，直接设img属性
                         imgObjPreview.style.display = 'block';
                         imgObjPreview.style.width = '300px';
                         imgObjPreview.style.height = '200px';

                         //火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式
                         imgObjPreview.src = window.URL.createObjectURL(docObj.files[]);
                     }
                     else {
                         //IE下，使用滤镜
                         docObj.select();
                         var imgSrc = document.selection.createRange().text;

                         //必须设置初始大小
                         localImagId.style.width = "300px";
                         localImagId.style.height = "200px";

                         //图片异常的捕捉，防止用户修改后缀来伪造图片
                         try {
                             localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
                             localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
                         }
                         catch (e) {
                             alert("您上传的图片格式不正确，请重新选择!");
                             return false;
                         }
                         imgObjPreview.style.display = 'none';
                         document.selection.empty();
                     }
                     return true;
                 }
             </script>
         </div>