js实现FileUpload选择图片后预览功能

时间：2024-01-15 23:46:38

当asp.net的FileUpload选择一个图片后不需要上传就能显示出图片的预览功能，

代码：

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>

<!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 runat="server">

    <title></title>

          <script type="text/javascript">

                                function selected(obj) {

                                    var str = "carpoolpic";

                                    str = str + obj.value;

                                    var imgSrc = document.getElementById(str).value;

                                    if (imgSrc == "" || imgSrc == null) {

                                        alert("此项没有图片");

                                        obj.checked = false;

                                    }

                                    changesrc(str);

                                }

                                var flag = true;

                                function changesrc(sender) {

                                    if (isFirefox = navigator.userAgent.indexOf("Firefox") > 0) {

                                        var imgSrc = document.getElementById(sender).value;

                                        var t = document.getElementById(sender);

                                        if (imgSrc == "") {

                                            flag = false;

                                            return false;

                                        }

                                        if (/(.*?)\.jpg$/.test(imgSrc.toLowerCase()) == false) {

                                            document.getElementById(sender).value = "";

                                            alert("只能选择jpg格式!");

                                            flag = false;

                                            return false;

                                        } else {

                                            var imgs = document.createElement("img");

                                            imgs.src = imgSrc;

                                            if (imgs.fileSize > 50 * 1024) {

                                                alert("图片大小不能超过 50 KB!");

                                                flag = false;

                                                return false;

                                            }

                                            flag = true;

                                        }

                                        document.getElementById("upImg").src = window.URL.createObjectURL(t.files[0]);

                                    } else {

                                        document.getElementById(sender).select();

                                        var imgSrc = document.selection.createRange().text;

                                        if (imgSrc == "") {

                                            flag = false;

                                            return false;

                                        }

                                        if (/(.*?)\.jpg$/.test(imgSrc.toLowerCase()) == false) {

                                            document.getElementById(sender).value = "";

                                            alert("只能选择jpg格式!");

                                            flag = false;

                                            return false;

                                        } else {

                                            var imgs = document.createElement("img");

                                            imgs.src = imgSrc;

                                            flag = true;

                                        }

                                        document.getElementById("upImg").src = imgSrc;

                                    }

                                }

                                function checkpic() {

                                    var raFlag = false;

                                    var obj = document.getElementsByName("select");

                                    for (var i = 0; i < obj.length; i++) {

                                        if (obj[i].checked) {

                                            raFlag = true;

                                            break;

                                        } else {

                                            raFlag = false;

                                        }

                                    }

                                    if (raFlag == false && flag == true) {

                                        alert("请选择最新的照片");

                                    }

                                    var subFlag = false;

                                    subFlage = flag && raFlag;

                                    flag = false;

                                    return subFlage;

                                }

                            </script>

</head>

<body>

    <form id="form1" runat="server">

    <div>  

<asp:FileUpload ID="fupweb_image" runat="server" class="chenck_upload left" onchange="changesrc(this.id)" /></span>

   <img id="upImg" runat="server" src=" "   />

    </div>

    </form>

</body>

</html>

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