Question

I’m trying to implement ZXing barcode scanner into my program. After getting the scanned result, I wanted to parse the result to a method named getData() which belong to another Java class. No syntax error on IDE, but mysql.getData(contents) won’t call the method no matter what. Please advise.

If I put this code under onCreate, the whole program force closed:

package com.posQR.ip;

import com.posQR.ip.MySQL;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class PosQRActivity extends Activity{
MySQL mysql;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);    
    mysql.getData("productID");
    Button button = (Button)findViewById(R.id.button1);
    button.setOnClickListener(scanListener);

}

public void onActivityResult(int requestCode, int resultCode, Intent intent) {

    TextView textView = (TextView)findViewById(R.id.textView1);
    if (requestCode == 0) {
    if (resultCode == RESULT_OK) {
    try {
        String contents = intent.getStringExtra("SCAN_RESULT");
        Toast.makeText(getApplicationContext(), contents + "from main", Toast.LENGTH_LONG).show();
        mysql.getData(contents);
        String string = Double.toString(mysql.getPrice());
        textView.setText(string);
    }
    catch (Exception e) {
        Toast.makeText(getApplicationContext(), "Please scan on the product's QR Code.", Toast.LENGTH_LONG).show();
    }
    } else if (resultCode == RESULT_CANCELED) {
    // Handle cancel
    }

    }
    }

    private OnClickListener scanListener = new OnClickListener() {
    public void onClick(View v) {
    try{
    Intent intent = new Intent("com.google.zxing.client.android.SCAN");
    intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
    startActivityForResult(intent, 0);
    }
    catch (Exception e){
    Toast.makeText(getApplicationContext(), "error opening scanner.", Toast.LENGTH_SHORT).show();
    }
    }
    };
}

.

package com.posQR.ip;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.content.Context;
import android.net.ParseException;
import android.util.Log;
import android.widget.Toast;

public class MySQL{
double Price;
private Context localContext;

public void getData(String productID) {
InputStream is = null;
String result = "";

Toast.makeText(localContext.getApplicationContext(), productID, Toast.LENGTH_LONG).show();

ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("id",productID));
//http post
try{
 HttpClient httpclient = new DefaultHttpClient();
 HttpPost httppost = new HttpPost("http://dl.dropbox.com/u/11233767/mysqlRequest.php");
 httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
 HttpResponse response = httpclient.execute(httppost);
 HttpEntity entity = response.getEntity();
 is = entity.getContent();
 }catch(Exception e){
     Log.e("log_tag", "Error in http connection"+e.toString());
}
//convert response to string
try {
BufferedReader br = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
    sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
// TODO: handle exception
Toast.makeText(localContext.getApplicationContext(), "Error converting result.",    Toast.LENGTH_LONG).show();
}

//paring data

try{
  JSONArray jArray = new JSONArray(result);
  JSONObject json_data=null;
         json_data = jArray.getJSONObject(0);
         Price=json_data.getDouble("price");

  }
  catch(JSONException e1){
      Toast.makeText(localContext.getApplicationContext(), "No City Found" ,Toast.LENGTH_LONG).show();
  } catch (ParseException e1) {
        e1.printStackTrace();
}
}

public double getPrice(){
return Price;
}

}

Answer 1

There are many problems here, such as:

1. the mysql variable is null when you use it in onCreate, you must declare it.

2. The localContext object in MySql is never initialized, which will cause another NullPointerException when you call getData(). You should create a constructor that accepts a Context object for the MySql class, and use that constructor when you’re fixing the first problem. Alternatively you could pass a Context object to getData()

3. the getData() method accesses the network in the main/UI thread, which will cause another Exception. Call this method in a different thread or spin off a new thread within the method itself. You may want to use an AsyncTask