how to make PHP server sends data to an Android device - php

Question

I want the Android device to send data to a PHP server. After receiving, the PHP server sends other data to Android. The first part can be done by using JSON. However, I don't know how to make the PHP server sends data to Android. Sorry, I am new to PHP!

Answer 1

I'm currently developing application that's communicating with PHP server (two-way communication, server sends data to application and application sends data to server), in objective-c [for iphone], but principle is same I guess.
We've used REST service with JSON.
In your case, it should work like this:
Mobile 1 sends data via REST call to REST server (it calls method1. Server is developed, for example, using Zend_REST.), it stores data in Database (mySQL for example).
Mobile 2 periodically sends request to REST server, to a method which checks for new entries in mySQL. If there's something new, it sends response with data, if not - it sends false.

Answer 2

Whatever data is "printed" by your PHP script will be returned in the response to the call made on the Android device.
You can do something like this in PHP:
<?php
// TODO: Handle incoming data
// Send JSON data back to client
header('Cache-Control: no-cache, must-revalidate');
header('Content-type: application/json');
// Compute data
$data = array(1, 2, 3, 4, 5, 6, 7, 8, 9);
// Encode/print data
echo json_encode($data);
?>
You would want to replace the first comment with your code to handle the data that was submitted from the client (Android). Then you set the response headers to be of type application/json and echo back your encoded data.
Technically you could echo/print back anything you would like, but using a format like JSON makes it much easier to decode the data on the client side.

Answer 3

Here is an Android snippet to send a POST request to some bogus website, sending email, password and a data string (you would put your json in the data string
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("http://website.com/yourPageHere.php");
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("email", emailString));
nameValuePairs.add(new BasicNameValuePair("password", passwordString));
nameValuePairs.add(new BasicNameValuePair("data", yourDataString));
try {
httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
} catch (UnsupportedEncodingException e) {
//do stuff
}
HttpResponse response = null;
try {
response = httpClient.execute(httpPost);
} catch (ClientProtocolException e) {
//do stuff
} catch (IOException e) {
//do stuff
}
if(response == null){
//time out or other problem, fail gracefully
}
HttpEntity responseEntity = response.getEntity();
try {
String jsonString = EntityUtils.toString(responseEntity);
//jsonString is the full body of the response from the server
//if your php script is sending json, thats whats in here
} catch (ParseException e) {
//do stuff
} catch (IOException e) {
//do stuff
}
Your php script, yourPageHere.php
Treat this just like any other php script you might write, except instead of returning html you are just returning a chunk of text representing json data.
<?php
header('Content-type: application/json');
/*
here you can use the $_POST['email'], $_POST['password']
and $_POST['data'] indexes to access the data sent to
you from the phone, then create a json string to return
to the phone
*/
/* you can convert php objects/arrays to json using
json_encode($object), handle this however you
want just so that $jsonString is the final
representation of the json object */
$jsonString = 'blabla';
/*
prints the string in the body of the response,
this is the "jsonString" object found in the
above android snippet.
*/
echo $jsonString; //
?>
You can do the above with GET requests instead of POST too.
If you are really new to PHP you might want to make a couple form page samples to get the hang of reading url parameters.

Answer 4

What you're looking for is some sort of AJAX call, allowing the HTTP GET request to stick around and wait for the server return value:
http://net.tutsplus.com/tutorials/javascript-ajax/5-ways-to-make-ajax-calls-with-jquery/