[Ajax]ajax入门

Ajax 2020-05-08

谈到ajax异步刷新技术，我之前感觉很高深，今天看了一下，大体上有一个了解，AJAX最大的应用就是我们要理解XMLHttpRequest这个对象。XMLHttpRequest可以提供不重新加载页面的情况下更新网页，在页面加载后在客户端向服务器请数 据， 在 页面加载后在服务器端接受数据，在后台向客户端发送数据。

关于ajax的详细叙述，可以参考这个博客：http://www.blogjava.net/tbwshc/archive/2012/07/24/383857.html

然后我贴出一些原始的ajax的例子，这样更方便了解ajax原理，解开他神奇的面纱，当然现在使用jQuery的ajax封装方法也非常方便。

例1：get请求

get.ashx:

<%@ WebHandler Language="C#" Class="_01_get" %>

using System;
using System.Web;

public class _01_get : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";
        //int m = 0;
        //int n = 5 / m;
        
        //System.Threading.Thread.Sleep(3000);
        context.Response.Write(DateTime.Now.ToString());
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}

get.htm: 

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <script type="text/javascript">
        //注意问题
        //1 请求的路径中不要有中文
        //2 注意大小写
        //3 设置不读缓存
        //4 区分readyState XMLHttpRequest的状态  和status http的状态码
        
        //1 创建对象
        var xhr = createXHR();
        function createXHR() {
            var request;
            if (XMLHttpRequest) {
                request = new XMLHttpRequest();
            
            } else {
                request = new ActiveXObject("Microsoft.XMLHTTP");
            }
            return request;
        }
        function btn_click() {
            
            document.getElementById("d").innerHTML = "正在加载...";           
            //2 初始化     
            xhr.open("get","01-get.ashx?_="+ Math.random(),true);
            //设置请求头 不读缓存
            //xhr.setRequestHeader("If-Modified-Since","0");
       
            //3 注册事件
            xhr.onreadystatechange = function () {
                //判断接收服务器的响应完成后
                if (xhr.readyState == 4) {
                    //判断服务器返回的状态码 
                    if (xhr.status == 200) {
                        //获取服务器返回的响应
                        //xhr.responseText
                        //xhr.responseXML
                        document.getElementById("d").innerHTML = xhr.responseText;
                    } else {
                        document.getElementById("d").innerHTML = "服务器内部错误";
                    }
                }
            }
            //4 发送请求
            xhr.send();
        }
        
    </script>
</head>
<body>
    <input type="button" value="get" onclick="btn_click()" />

    <div id="d"></div>
</body>
</html>

例2：post请求提交保单

post.ashx:

<%@ WebHandler Language="C#" Class="_02_post" %>

using System;
using System.Web;

public class _02_post : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";

        string name = context.Request.Form["n"];
        string pwd = context.Request.Form["p"];
        if (name == "admin" && pwd == "admin")
        {
            context.Response.Write(1);
        }
        else
        {
            context.Response.Write(0);
        }
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}


post.htm:

<!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>
    <title></title>
    <script type="text/javascript">
        //1 创建对象
        var xhr = createXHR();
        function createXHR() {
            var request;
            if (XMLHttpRequest) {
                request = new XMLHttpRequest();
            } else {
                request = new ActiveXObject("Microsoft.XMLHTTP");
            }
            return request;
        }
        function btn_click() {
            var name = my$("txtName").value;
            var pwd = my$("txtPwd").value;
            var data = "n=" + name + "&p=" + pwd;
            
            //2
            xhr.open("post","02-post.ashx",true);
            //!------------------!注意
            xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
            //3
            xhr.onreadystatechange = function () {
                if (xhr.readyState == 4) {
                    if (xhr.status == 200) {
                        var m = xhr.responseText;
                        if (m == 1) {
                            my$("msg").innerHTML = "登录成功";
                        } else {
                            my$("msg").innerHTML = "登录失败";
                        }
                    } else {
                        my$("msg").innerHTML = "服务器内部错误";
                    }
                }
            }
            //4
            xhr.send(data);
        }

        function my$(id) {
            return document.getElementById(id);
        }
    </script>
</head>
<body>
    <input type="text" id="txtName" /><br />
    <input type="text" id="txtPwd" /><br />
    <input type="button" value="Login" onclick="btn_click()" />
    <span id="msg"></span>
</body>
</html>

例3：省市选择效果

pro.ashx:

<%@ WebHandler Language="C#" Class="_06_pro" %>

using System;
using System.Web;
using System.Collections.Generic;
using System.Text;
public class _06_pro : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";
        string s = context.Request.QueryString["pid"];
        int pid;
        if (int.TryParse(s,out pid))
        { 
            //json形式的字符串
            string json = GetDataByPId(pid);
            context.Response.Write(json);
        }
        else    
        {
            context.Response.Write("[]");
        }
    }
    private string GetDataByPId(int pid)
    {
        List<Data> list = GetAllDatas();

        List<Data> wantedList = new List<Data>();
        foreach (Data data in list)
        {
            if (data.Pid == pid)
            {
                wantedList.Add(data);
            }
        }
        
        //拼json形式的字符串   
         //[{ "Id": 1,"Name": "河北省","PId": 0 },//            { "Id": 2,"Name": "日本省",//            { "Id": 3,"Name": "台湾省","PId": 0 }
         // ]
        StringBuilder sb = new StringBuilder();
        sb.Append("[");

        foreach (Data data in wantedList)
        {
            sb.Append("{ \"Id\": "+data.Id+",\"Name\": \""+data.Name+"\",\"PId\": "+data.Pid+" },");
        }
        sb.Remove(sb.Length - 1,1);
        sb.Append("]");
        return sb.ToString();
    }
    
    /// <summary>
    /// 模拟从数据库中加载数据，返回泛型集合
    /// </summary>
    /// <returns></returns>
    private List<Data> GetAllDatas()
    {
        List<Data> list = new List<Data>();

        list.Add(new Data() { Id = 1,Name = "河北省",Pid = 0 });
        list.Add(new Data() { Id = 2,Name = "台湾省",Pid = 0 });
        list.Add(new Data() { Id = 3,Name = "日本省",Pid = 0 });


        list.Add(new Data() { Id = 4,Name = "石家庄",Pid = 1 });
        list.Add(new Data() { Id = 5,Name = "邯郸市",Pid = 1 });
        list.Add(new Data() { Id = 6,Name = "邢台市",Pid = 1 });

        list.Add(new Data() { Id = 7,Name = "高雄市",Pid = 2 });
        list.Add(new Data() { Id = 8,Name = "台北",Pid = 2 });
        list.Add(new Data() { Id = 9,Name = "台中",Pid = 2 });

        list.Add(new Data() { Id = 10,Name = "东京",Pid = 3 });
        list.Add(new Data() { Id = 11,Name = "冲绳",Pid = 3 });
        list.Add(new Data() { Id = 12,Name = "大阪",Pid = 3 });
        return list;
    }
    public bool IsReusable {
        get {
            return false;
        }
    }

}

pro.htm: 

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <script src="ajax.js" type="text/javascript"></script>
    <script type="text/javascript">
        window.onload = function () {
            loadProvince();

            
        }
        function loadProvince() {
            var province = my$("province");
            //发送异步请求获取省的数据
            ajax("get","06-pro.ashx?pid=0",null,function (s) {
                //把字符串转化成对象
                var array = eval(s);
                for (var i = 0; i < array.length; i++) {
                    var json = array[i];
                    var option = document.createElement("option");
                    option.innerHTML = json.Name;
                    option.value = json.Id;
                    province.appendChild(option);
                }
                //当省加载完，再加载市
                loadCity();

            },function () {
                alert("服务器内部错误");
            });
        }

        function loadCity() {
            var pid = my$("province").value;
            var city = my$("city");
            //清空下拉框
            city.innerHTML = "";

            ajax("get","06-pro.ashx?pid=" + pid,function (s) {
                //把字符串转化成对象
                var array = eval(s);
                for (var i = 0; i < array.length; i++) {
                    var json = array[i];
                    var option = document.createElement("option");
                    option.innerHTML = json.Name;
                    option.value = json.Id;
                    city.appendChild(option);
                }
            },function () {
                alert("服务器内部错误");
            });
        }

    </script>
</head>
<body>
    <select id="province" onchange="loadCity()">
    </select>
    <select id="city">
    </select>
</body>
</html>

自己封装的ajax：

function my$(id) {
    return document.getElementById(id);
}

var xhr = createXHR();
function createXHR() {
    var request;
    if (XMLHttpRequest) {
        request = new XMLHttpRequest();

    } else {
        request = new ActiveXObject("Microsoft.XMLHTTP");
    }
    return request;
}

function ajax(method,url,data,fnSuccess,fnError) {

    xhr.open(method,true);
    if (method == "post") {
        //!------------------!注意
        xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    }
    xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
          
            if (xhr.status == 200) {
                var s = xhr.responseText;
                fnSuccess(s);
            } else {
                fnError();
            }
        }
    }
    xhr.send(data);
}

这里要感谢刘兄的指导，在此鸣谢！

==================== 迂者 丁小未 CSDN博客专栏=================

MyBlog：http://blog.csdn.net/dingxiaowei2013 MyQQ:1213250243

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转载请注明出处：http://blog.csdn.net/dingxiaowei2013/article/details/17130553

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