XMLHttpRequest在PHP脚本运行时获取数据

问题描述：

I am trying to poll a PHP page for an updated $val variable value, but for some reason it doesn't want to show anything on the calling html page

PHP (generator.php) script:

<?php

header('Content-type: text/html; charset=utf-8');
function output($val)
{
echo $val;


    flush();
    ob_flush();
    usleep(500000);
}
output('Begin... (counting to 10)');
for( $i = 0 ; $i < 10 ; $i++ )
{
    output($i+1);
}
output('End...');

?>

HTML page:

<html>
<head>
<script type="text/javascript">

function generate(){

    try {
        xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
    } catch(e) {
    }

    xmlhttp.onreadystatechange = refreshwait;
    xmlhttp.open('GET', './generator.php', true);
    xmlhttp.send('null');

}

function refreshwait() {

    if (xmlhttp.readyState == 4){

        if(xmlhttp.status == 200){

            var code = 'Finished';
            document.getElementById('view_area').innerHTML = code;  
        }

    }else{

        document.getElementById("view_area").innerHTML = xmlhttp.responseText;          
        refreshwait();
    }

}

</script>
</head>
<body>
<div id="a_form">
<form id="aform">
<input name="Generate" onClick="generate()" type="button" value="Generate Fresh File" />
</form>
</div>
<div id="view_area"></div>
</body>
</html>

What am I doing wrong? I am expecting to see a count from 1 to 10 appear on the html page as the php is running.

我正在尝试轮询PHP页面以获取更新的$ val变量值，但由于某种原因它不会想要在调用html页面上显示任何内容 p>

PHP（generator.php）脚本： p>

 ＆lt;？php 
 
header  （'Content-type：text / html; charset = utf-8'）; 
function output（$ val）
 {
echo $ val; 
 
 
 flush（）; 
 ob_flush（）; \  n usleep（500000）; 
} 
output（'Begin ...（count to 10）'）; 
for（$ i = 0; $ i＆lt; 10; $ i ++）
 {
 output（$  i + 1）; 
} 
output（'结束...'）; 
 
？＆gt; 
  code>  pre> 
 
  HTML页面： p>  
 
 
 ＆lt; html＆gt; 
＆lt; head＆gt; 
＆lt; script type =“text / javascript”＆gt; 
 
function generate（）{
 
 try {
 xmlhttp =  window.XMLHttpRequest？  new XMLHttpRequest（）：new ActiveXObject（“Microsoft.XMLHTTP”）; 
} catch（e）{
} 
 
 xmlhttp.onreadystatechange = refreshwait; 
 xmlhttp.open（'GET'，'。/ generator）  .php'，true）; 
 xmlhttp.send（'null'）; 
 
} 
 
函数refreshwait（）{
 
 if if（xmlhttp.readyState == 4）{
 
 if  （xmlhttp.status == 200）{
 
 var code ='Finished'; 
 document.getElementById（'view_area'）。innerHTML = code;  
} 
 
} else {
 
 document.getElementById（“view_area”）。innerHTML = xmlhttp.responseText;  
 refreshwait（）; 
} 
 
} 
 
＆lt; / script＆gt; 
＆lt; / head＆gt; 
＆lt; body＆gt; 
＆lt; div id =“a_form”＆gt; 
＆lt; form id =  “aform”＆gt; 
＆lt;输入名称=“生成”onClick =“generate（）”type =“button”value =“生成新文件”/＆gt; 
＆lt; / form＆gt; 
＆lt; / div＆gt; 
＆lt;  ; div id =“view_area”＆gt;＆lt; / div＆gt; 
＆lt; / body＆gt; 
＆lt; / html＆gt; 
  code>  pre> 
 
 我做错了什么？ 因为php正在运行，我希望看到html页面上出现1到10的计数。 p> 
  div>

答

I can think of four potential issues:

Some servers (SAPIs) feature internal output buffering, typically to a size of 4Kb. This is because sending "chunks" of this size is generally more efficient than sending many smaller pieces.
Some browsers will read chunks of a certain size (again, typically 4Kb) before rendering them to the document. This again improves performance by not re-rendering the page every time a few bytes happen to show up in the network stream.
Some browsers (particularly older IE, can't remember which version) do not allow access to responseText until the readyState is 4. Obviously this is a limitation, and it has been removed in newer browsers, but it's still a possible problem.
EDIT: Some browsers require you to define onreadystatechange after calling .open(). This is to allow reuse of XMLHttpRequest objects. Calling .open effectively "resets" the object.

Possible solution: Assuming the problem is 1 or 2, rather than 3 or 4, then you can try outputting echo $val.str_repeat(" ",5000); to try and circumvent the output buffering. Obviously this will bloat your bandwidth, but the result should look the same (because spaces are collapsed in HTML)

XMLHttpRequest在PHP脚本运行时获取数据

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