Question

I have created an application to parse data and putting it into a string array. I am doing this task in background. What I want to implement is, to read the string for whatever data the background process has parsed. In order to do that, I have made the array static and I am trying to read from it in another class, but my program is failing with the following error. Could anyone please take a look and help me out. Thanks.

01-17 09:43:07.927: E/AndroidRuntime(1167): FATAL EXCEPTION: main
01-17 09:43:07.927: E/AndroidRuntime(1167): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.pro1/com.example.pro1.Secactivity}: java.lang.NullPointerException
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.os.Looper.loop(Looper.java:137)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread.main(ActivityThread.java:5039)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at java.lang.reflect.Method.invokeNative(Native Method)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at java.lang.reflect.Method.invoke(Method.java:511)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at dalvik.system.NativeStart.main(Native Method)
01-17 09:43:07.927: E/AndroidRuntime(1167): Caused by: java.lang.NullPointerException
01-17 09:43:07.927: E/AndroidRuntime(1167):     at com.example.pro1.Secactivity.onCreate(Secactivity.java:29)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.Activity.performCreate(Activity.java:5104)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-17 09:43:07.927: E/AndroidRuntime(1167):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-17 09:43:07.927: E/AndroidRuntime(1167):     ... 11 more

Here is my main class where I am executing the asynctask:

public class MainActivity extends Activity {
    EditText uid;
    EditText password;
    Button submit;
    static String Sarray1[] = new String[50];
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        submit = (Button)findViewById(R.id.submit);
        submit.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                uid = (EditText)findViewById(R.id.id);
                password = (EditText)findViewById(R.id.password);
                String userid = uid.getText().toString();
                String pwd = password.getText().toString();
                Loginauth log = new Loginauth();
                if(!userid.equals("")&&!pwd.equals(""))
                {
                    String result = log.Login(userid,pwd);
                    if(result.equals(""))
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "Login Error: Check id and Password", Toast.LENGTH_LONG);
                        toast.show();
                    }
                    else
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "Login Successfull", Toast.LENGTH_SHORT);
                        toast.show();
                        SAXParserActivity ab = new SAXParserActivity();
                        ab.execute();
                        for (int j = 0; j<15;j++)
                    {
                        Log.d("Array",Sarray1[j].toString());
                    }
                        startActivity(new Intent("com.example.pro1.ABC"));
                    }

                }
                else
                {
                    Toast toast = Toast.makeText(getApplicationContext(), "Invalid id or password", Toast.LENGTH_LONG);
                    toast.show();
                }

            }
        });


    }
    class SAXParserActivity extends AsyncTask<Void,Void,Void> {

        XMLGettersSetters data;
        @Override
        protected Void doInBackground(Void... params) {
            Log.i("Abe","Abe");
            try {
                SAXParserFactory saxPF = SAXParserFactory.newInstance();
                SAXParser saxP = saxPF.newSAXParser();
                XMLReader xmlR = saxP.getXMLReader();
                URL url = new URL("http://www.xmlfiles.com/examples/cd_catalog.xml"); // URL of the XML             
                XMLHandler myXMLHandler = new XMLHandler();
                xmlR.setContentHandler(myXMLHandler);
                xmlR.parse(new InputSource(url.openStream()));

            } catch (Exception e) {
                System.out.println(e);
            }

            data = XMLHandler.data;                 
            for (int i = 0; i < data.getTitle().size(); i++) {

                Sarray1[i] =data.getTitle().get(i);
                //System.out.printf("Sarray",Sarray[i].toString());
                //Log.d("Abe",Sarray);
                //Sarray1[i]=Sarray;

                Log.d("Abe",Sarray1[i].toString());
            }

            return null;
        }
    }


}

Here is the class from where I am trying to access the array:

package com.example.pro1;


import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.widget.TabHost;

public class Secactivity extends FragmentActivity {
    TabHost tHost;



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main1);

    tHost = (TabHost) findViewById(android.R.id.tabhost);
    tHost.setup();
    String array[] = new String[50];
    for(int i = 0;i<MainActivity.Sarray1.length;i++)
    {
        array[i] = MainActivity.Sarray1[i];
        Log.d("Secactivity",MainActivity.Sarray1[i]);
    }

    /** Defining Tab Change Listener event. This is invoked when tab is changed */
    TabHost.OnTabChangeListener tabChangeListener = new TabHost.OnTabChangeListener() {

            @Override
            public void onTabChanged(String tabId) {
                android.support.v4.app.FragmentManager fm =   getSupportFragmentManager();
                Protab1 androidFragment = (Protab1) fm.findFragmentByTag("ST");
                Protab2 appleFragment = (Protab2) fm.findFragmentByTag("CSI");
                android.support.v4.app.FragmentTransaction ft = fm.beginTransaction();

                /** Detaches the androidfragment if exists */
                if(androidFragment!=null)
                    ft.detach(androidFragment);

                /** Detaches the applefragment if exists */
                if(appleFragment!=null)
                    ft.detach(appleFragment);

                /** If current tab is android */
                if(tabId.equalsIgnoreCase("ST")){

                    if(androidFragment==null){      
                        /** Create AndroidFragment and adding to fragmenttransaction */
                        ft.add(R.id.realtabcontent,new Protab1(), "ST");                        
                    }else{
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        ft.attach(androidFragment);                     
                    }

                }else{  /** If current tab is apple */
                    if(appleFragment==null){
                        /** Create AppleFragment and adding to fragmenttransaction */
                        ft.add(R.id.realtabcontent,new Protab2(), "CSI");                       
                    }else{
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        ft.attach(appleFragment);                       
                    }
                }
                ft.commit();                
            }
        };


        /** Setting tabchangelistener for the tab */
        tHost.setOnTabChangedListener(tabChangeListener);

        /** Defining tab builder for Andriod tab */
    TabHost.TabSpec tSpecAndroid = tHost.newTabSpec("ST");
    tSpecAndroid.setIndicator("ST");        
    tSpecAndroid.setContent(new DummyTabContent(getBaseContext()));
    tHost.addTab(tSpecAndroid);


    /** Defining tab builder for Apple tab */
    TabHost.TabSpec tSpecApple = tHost.newTabSpec("CSI");
    tSpecApple.setIndicator("CSI");        
    tSpecApple.setContent(new DummyTabContent(getBaseContext()));
    tHost.addTab(tSpecApple);

}   

}

Answer 1

Don’t use fix sized Array like this,

static String Sarray1[] = new String[50];

Change that to ArrayList,

ArrayList<String> Sarray1 = new ArrayList<String>();

And then add data to that to use furhter,

Sarray1.add(data.getTitle().get(i));

In your case if you loop with MainActivity.Sarray1.length then it will always run for 50 times even though there is only 10 data entries. So there are changes of getting null values for remaining indexes.