Adding an Imageview drawable to a listview Imageview item at Runtime gives null pointer exception

Question

This is my listviewite.xml with the following structure, when the app is running and it reaches the getFavourite() it force closes. I would like to know the reason from any assistance. I think the problem is in the xml structure, is it? Help.

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:baselineAligned="false"
    android:gravity="left|center"
    android:paddingBottom="5px"
    android:paddingLeft="5px"
    android:paddingTop="5px" >

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="fill_parent" >

        <ImageView
            android:id="@+id/avatar"
            android:layout_width="wrap_content"
            android:layout_height="fill_parent"
            android:layout_centerVertical="true"
            android:layout_marginRight="6dip"
            android:visibility="gone" />

        <ImageView
            android:id="@+id/imgbtn_favorite"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:layout_alignBottom="@+id/avatar"
            android:layout_alignParentRight="true"
            android:layout_marginRight="6dp"
            android:indeterminate="true"
            android:maxHeight="30dip"
            android:maxWidth="30dip"
            android:minHeight="30dip"
            android:minWidth="30dip"
            android:contentDescription="@string/favorites" />

        <ProgressBar
            android:id="@+id/progress_bar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:layout_marginRight="6dip"
            android:indeterminate="true"
            android:maxHeight="30dip"
            android:maxWidth="30dip"
            android:minHeight="30dip"
            android:minWidth="30dip" />
    </RelativeLayout>

    <LinearLayout
        android:layout_width="0dip"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/username"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center" />

        <TextView
            android:id="@+id/message"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10px"
            android:textColor="#0099CC" />
    </LinearLayout>

</LinearLayout>

This is the getFavourite() method below:

imageManager.displayImage(tweet.image_url, activity, holder.image,holder.progress); // CHANGED

            /*If a product exists in shared preferences then set heart_red drawable
             * and set a tag*/
          if (checkFavoriteItem(tweet)) {
                holder.favoriteImg.setImageResource(R.drawable.heart_red);
                holder.favoriteImg.setTag("red");
            } else {
                holder.favoriteImg.setImageResource(R.drawable.heart_grey);
                holder.favoriteImg.setTag("grey");
            }
        }
        return v;
    }

    /* Checks whether a particular product exists in SharedPreferences */
    public boolean checkFavoriteItem(Tweet checkTweet) {

        boolean check = false;
        List<Tweet> favorites = sharedPreference.getFavorites(context);
        if (favorites != null) {
            for (Tweet tweet : favorites) {
                if (tweet.equals(checkTweet)) {
                    check = true;
                    break;
                }
            }
        }
        return check;
    }

public ArrayList<Tweet> getFavorites(Context context) {
        SharedPreferences settings;
        List<Tweet> favorites;

        settings = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);

        if (settings.contains(FAVORITES)) {
            String jsonFavorites = settings.getString(FAVORITES, null);
            Gson gson = new Gson();
            Tweet[] favoriteItems = gson.fromJson(jsonFavorites, Tweet[].class);

            favorites = Arrays.asList(favoriteItems);
            favorites = new ArrayList<Tweet>(favorites);
        } else
            return null;

        return (ArrayList<Tweet>) favorites;
    }

This is the adapter code: Requested

public class TweetItemAdapter extends ArrayAdapter<Tweet> {

    private ArrayList<Tweet> tweets;
    private Activity activity;
    private Context context;
    public ImageManager imageManager;
    public SharedPreference sharedPreference;

    public TweetItemAdapter(Activity a, int textViewResourceId, ArrayList<Tweet> tweets) {
        super(a, textViewResourceId, tweets);
        this.tweets = tweets;
        activity = a;

        sharedPreference = new SharedPreference();
        imageManager = new ImageManager(activity.getApplicationContext());
    }



    public static class ViewHolder {
        public TextView username;
        public TextView message;
        public ImageView image;
        public ProgressBar progress; // ADDED
        public ImageView favoriteImg;
    }

    @Override
    public int getCount() {
        return tweets.size();
    }

    @Override
    public Tweet getItem(int position) {
        return tweets.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        ViewHolder holder;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.listitem, null);
            holder = new ViewHolder();
            holder.username = (TextView) v.findViewById(R.id.username);
            holder.message = (TextView) v.findViewById(R.id.message);
            holder.image = (ImageView) v.findViewById(R.id.avatar);
            holder.progress = (ProgressBar) v.findViewById(R.id.progress_bar); // ADDED
            holder.favoriteImg = (ImageView) v.findViewById(R.id.imgbtn_favorite);
            v.setTag(holder);
        } else
            holder = (ViewHolder) v.getTag();

        final Tweet tweet = tweets.get(position);
        if (tweet != null) {
            holder.username.setText(tweet.username);
            holder.message.setText(tweet.message);
            holder.image.setTag(tweet.image_url);
            imageManager.displayImage(tweet.image_url, activity, holder.image,holder.progress); // CHANGED

            /*If a product exists in shared preferences then set heart_red drawable
             * and set a tag*/
          if (checkFavoriteItem(tweet)) {
                holder.favoriteImg.setImageResource(R.drawable.heart_red);
                holder.favoriteImg.setTag("red");
            } else {
                holder.favoriteImg.setImageResource(R.drawable.heart_grey);
                holder.favoriteImg.setTag("grey");
            }
        }
        return v;
    }

    /* Checks whether a particular product exists in SharedPreferences */
    public boolean checkFavoriteItem(Tweet checkTweet) {

        boolean check = false;
        List<Tweet> favorites = sharedPreference.getFavorites(context);
        if (favorites != null) {
            for (Tweet tweet : favorites) {
                if (tweet.equals(checkTweet)) {
                    check = true;
                    break;
                }
            }
        }
        return check;
    }

    @Override
    public void add(Tweet tweet) {
        super.add(tweet);
        tweets.add(tweet);
        notifyDataSetChanged();
    }

    @Override
    public void remove(Tweet tweet) {
        super.remove(tweet);
        tweets.remove(tweet);
        notifyDataSetChanged();
    }   

}

Logcat:

07-12 09:49:11.312: E/AndroidRuntime(8857): FATAL EXCEPTION: main
    07-12 09:49:11.312: E/AndroidRuntime(8857): java.lang.NullPointerException
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at com.rowland.preferences.SharedPreference.getFavorites(SharedPreference.java:65)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at com.rowland.adapters.TweetItemAdapter.checkFavoriteItem(TweetItemAdapter.java:114)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at com.rowland.adapters.TweetItemAdapter.getView(TweetItemAdapter.java:99)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.AbsListView.obtainView(AbsListView.java:1593)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.ListView.makeAndAddView(ListView.java:1782)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.ListView.fillDown(ListView.java:705)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.ListView.fillFromTop(ListView.java:762)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.ListView.layoutChildren(ListView.java:1633)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.AbsListView.onLayout(AbsListView.java:1423)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.onLayout(LinearLayout.java:1047)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.LinearLayout.onLayout(LinearLayout.java:1047)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.View.layout(View.java:7175)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.ViewRoot.performTraversals(ViewRoot.java:1146)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1865)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.os.Handler.dispatchMessage(Handler.java:99)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.os.Looper.loop(Looper.java:130)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at android.app.ActivityThread.main(ActivityThread.java:3687)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at java.lang.reflect.Method.invokeNative(Native Method)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at java.lang.reflect.Method.invoke(Method.java:507)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
    07-12 09:49:11.312: E/AndroidRuntime(8857):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

You did not initialize context in your adapter constructor. You're passing it to getFavorites() and calling a method on it causes the NPE.