Android, Connecting to MySQL using PHP: Null Pointer exception - php

Question

Im a newbie to android, I am learning to connect to a server through android client using Php, MySql and JSON. For testing purpose im running on localhost.
So for here's what I've done.
Database demo.php
public class Database_demo extends ListActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String result = null;
InputStream is = null;
StringBuilder sb = null;
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
List<String> r = new ArrayList<String>();
try{
//http post
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://10.0.2.2/PhpAndMySql/category.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}
catch(Exception e){
Toast.makeText(getBaseContext(),e.toString() ,Toast.LENGTH_LONG).show();
}
//Convert response to string
try
{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"UTF-8"));
sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null)
{
sb.append(line + "\n");
}
is.close();
result = sb.toString();
}
catch(Exception e)
{
Toast.makeText(getBaseContext(),e.toString() ,Toast.LENGTH_LONG).show();
}
//END Convert response to string
try{
JSONArray jArray = new JSONArray(result);
JSONObject json_data=null;
for(int i=0;i<jArray.length();i++)
{
json_data = jArray.getJSONObject(i);
r.add(json_data.getString("category"));
}
setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, r));
}
catch(JSONException e1){
Toast.makeText(getBaseContext(),e1.toString() ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
Toast.makeText(getBaseContext(),e1.toString() ,Toast.LENGTH_LONG).show();
}
}
}
category.php
<?php
mysql_connect("localhost","root","");
mysql_select_db("test");
$q=mysql_query("SELECT * FROM category ORDER BY 'category'.'category' ASC");
while($row=mysql_fetch_assoc($sql))
$output[]=$row;
print(json_encode($output));
mysql_close();
?>
MySQL
CREATE TABLE `test`.`category` (
`category_id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`category` VARCHAR( 255 ) NOT NULL
) ENGINE = MYISAM ;
I am getting a NullPointer Exception, when I execute in android.
Is the Php File correct?
Please I need your help with this!
Thanks

Answer 1

I'm thinking your php should be as follows (instead of quotes on the table.column use backticks).
<?php
mysql_connect("localhost","root","");
mysql_select_db("test");
$q=mysql_query("SELECT * FROM category ORDER BY `category` ASC");
$output = array();
while($row = mysql_fetch_assoc($sql))
$output[]=$row;
print(json_encode($output));
mysql_close();
?>