Android: Getting Empty String From Php webpage - php

Question

I have two applications, one I send long. and latitude coordinates to a php file and the other application retrieves the long. and lat. coords. In order to test and see if I could get the first working I create a function I posted the latitude and long. coords two the php service and I got them back in the same Application. I placed them in a toast to see if it works. I even implemented location listener to upload the coordinates and retrieve them in the same application to test before trying to receive them in the other application. It works fine. But when I try to use the same code in the other application for receiving the coordinates, I receive blank coordinates. I debugged it and its just blank, as if when I make the call to the server from the other application it erases the current values in the php service.
Code for placing the coordinates in application one:
public void postData(String longCord, String latCord) throws JSONException{
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(".../android/serverFile.php");
JSONObject json = new JSONObject();
try {
// JSON data:
json.put("longitude", longCord);
json.put("latitude", latCord);
JSONArray postjson=new JSONArray();
postjson.put(json);
// Post the data:
httppost.setHeader("json",json.toString());
httppost.getParams().setParameter("jsonpost",postjson);
// Execute HTTP Post Request
//System.out.print(json);
HttpResponse response = httpclient.execute(httppost);
// for JSON:
if(response != null)
{
InputStream is = response.getEntity().getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
JSONObject jsonObj = new JSONObject(jsonStr);
// grabbing the menu object
String longitudecord = jsonObj.getString("lon");
String latitudecord = jsonObj.getString("lat");
Toast.makeText( getApplicationContext(),longitudecord,Toast.LENGTH_SHORT).show();
Toast.makeText( getApplicationContext(),latitudecord,Toast.LENGTH_SHORT).show();
}
}catch (ClientProtocolException e) {
// TODO Auto-generated catch block
} catch (IOException e) {
// TODO Auto-generated catch block
}
}
php file:
<?php
$json = $_SERVER['HTTP_JSON'];
$data = json_decode($json);
$lon = $data->longitude;
$lat = $data->latitude;
$variable = array( 'lon' => "$lon", 'lat' => "$lat" );
// One JSON for both variables
echo json_encode($variable);
?>
Now when I run this code on the other application...Its the same as above minus posting the coordinates...I get lon:"" and lat:"". Sort of like by making the request it has somehow erased the info that was posted by other application. Is this the case?
public void recieveData() throws JSONException{
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(".../android/serverFile.php");
try {
HttpResponse response = httpclient.execute(httppost);
// for JSON:
if(response != null)
{
InputStream is = response.getEntity().getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
String jsonStr = sb.toString();
JSONObject jsonObj = new JSONObject(jsonStr);
// grabbing the menu object
String longitudecord = jsonObj.getString("lon");
String latitudecord = jsonObj.getString("lat");
Toast.makeText( getApplicationContext(),longitudecord,Toast.LENGTH_SHORT).show();
Toast.makeText( getApplicationContext(),jsonStr,Toast.LENGTH_SHORT).show();
}

Answer 1

Try to access your URL in browser and make sure your PHP script does not give any errors in the following lines (since you don't supply any JSON input in the second application):
$data = json_decode($json);
$lon = $data->longitude;
$lat = $data->latitude;
Also, it would be nice to hear, how'd you save your lat/lon on the server, so they persist between the calls.
For example, you may use this PHP code:
$db_host = "localhost";
$db_name = "********";
$db_user = "********";
$db_pass = "********";
// connect to MySQL
$db = mysql_connect($db_host, $db_user, $db_pass);
if( !$db ) {
die( 'Unable to connect to server : ' . mysql_error() );
}
// select the DB
if( !mysql_select_db($db_name) ) {
die( 'Unable to select DB : ' . mysql_error() );
}
// create table, if not exists
if( !mysql_query( "CREATE TABLE IF NOT EXISTS `locations` (
`id` int(11) NOT NULL auto_increment,
`latitude` double NOT NULL COMMENT 'latitude',
`longitude` double NOT NULL COMMENT 'longitude',
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;"
) ) {
die( 'Unable to create table : ' . mysql_error() );
}
// save values
mysql_query( "INSERT INTO locations (`latitude`, `longitude`) VALUES ( '$lat', '$lon')" );
// read them back
$track = array()
$result = mysql_query( "SELECT * FROM locations" );
while( $data = mysql_fetch_assoc($result) ) {
$track[] = array(
'latitude' => $data['latitude'],
'longitude' => $data['longitude'] );
}
// here you may convert `track` into JSON / XML and send coordinates list to your application