Question

I have an activity that lets the user load some data when they press a button. That data is passed to a list and each list item has different data stored in it. When they click on the list item it launches an intent which passes them to a new class.

But when I store the first value returned from pressing this button, i.e. using the onStop() and using SharedPreferences, and click on it I get an error. I think it may be something to do with the intent – the list item just isn’t attaching to it. Here is part of the code:

adapter = new ArrayAdapter<String>( this, android.R.layout.simple_list_item_1, listItems );
    setListAdapter( adapter );

    list = getListView();
    list.setOnItemClickListener( this );

    if( settings.contains( "ARRAY_LIST_VALUE_0" ) )
    {
        listItems.add( 0, settings.getString( "ARRAY_LIST_VALUE_0",tempStore ) );   
        adapter.notifyDataSetChanged();
    }
    reload = (Button)findViewById( R.id.reloadTen );
    reload.setOnClickListener( this );

    // Original onItemClicked was in here
    list.setTextFilterEnabled( true );  
}


@Override
public void onItemClick(AdapterView<?> arg0, View listItem, int position, long arg3) 
{
    // Start an activity based on what list view item is pressed
    Intent intent = new Intent( newSightings.this, newCompass.class );

    // Pass the data we retrieved to the next activity
    intent.putExtra( "info",data[position]  );
    startActivity( intent );
}

@Override
protected void onStop() 
{
    super.onStop();

    SharedPreferences settings = getSharedPreferences( PREFS_NAME,0 );
    SharedPreferences.Editor editor = settings.edit();

    if( usrPrssdBtn )
    {   
            // Store the latitude and longitude values and then reload them if known
            editor.putString( "LAT",myNewLat );
            editor.putString( "LONG",myNewLon );

            // Place first element of array list in storage
            if( adapter.getCount() > 0 )
            {
                Toast.makeText( getApplicationContext(), "Leaving Activity, Adapter Size: "+ adapter.getCount()+"\nStoring: "+listItems.get( 0 ).toString(), Toast.LENGTH_SHORT ).show();
                tempStore = listItems.get( 0 ).toString();

                editor.putString( "ARRAY_LIST_VALUE_0",tempStore );
                editor.putString( "DATA",data[arryTrckr] );  
            }
    }
    editor.commit();

}

So – when I run the activity and then press back, then go back to the activity the stored list item is there. Problem is when I click it it crashes the app. What’s the problem? I get a NullPointerException at this line:

intent.putExtra( "info",data[position] ); 

Answer 1

adapter = new ArrayAdapter( this, android.R.layout.simple_list_item_1, listItems );

in the above line you are using listitems array to sidplay the data.
where as onItemclick event you are using

data[position] to fetch the data according to me when you are displaying data from listitems array the you must use listitems[position] to fetch the data