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Android Android Lists and Adapters (2015) Using Parcelable Data Updating the Daily Forecast UI

Crash on Daily Forecast list scroll

I'm recieveing a NullPointerException when my list attempts to scroll on the Daily Forecast activity. The exception points to the ImageView fore the forecast icon. My code is listed below.

NullPointerException:

java.lang.NullPointerException: Attempt to read from field 'android.widget.ImageView com.kevmhaube.stormy.adapters.DayAdapter$ViewHolder.iconImageView' on a null object reference
            at com.kevmhaube.stormy.adapters.DayAdapter.getView(DayAdapter.java:58)

DayAdapter:

public class DayAdapter extends BaseAdapter {

    private Context mContext;
    private Day[] mDays;
    private ViewHolder holder;

    public DayAdapter(Context context, Day[] days) {
        mContext = context;
        mDays = days;
    }

    //Some code removed for length

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(R.layout.daily_list_item, null);
            holder = new ViewHolder();
            holder.iconImageView = (ImageView) convertView.findViewById(R.id.iconImageView);
            holder.tempLabel = (TextView) convertView.findViewById(R.id.tempLabel);
            holder.dayLabel = (TextView) convertView.findViewById(R.id.dayNameLabel);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        Day day = mDays[position];
        if (day != null) {
            holder.iconImageView.setImageResource(day.getIconId()); //Line of code with NullPointer
            holder.tempLabel.setText(Double.toString(day.getTempMax()));
        }

        if (position == 0) {
            holder.dayLabel.setText("Today");
        } else {
            holder.dayLabel.setText(day.getDayOfTheWeek());
        }

        return convertView;
    }

    //ViewHolder inner class!
    private static class ViewHolder {
        ImageView iconImageView;
        TextView tempLabel;
        TextView dayLabel;
    }
}

2 Answers

You need to declare holder as a ViewHolder just after the opening of the getView function

@Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        if(convertView == null) {
            convertView = LayoutInflater.from(mContxt).inflate(R.layout.daily_list_item, null);
            holder = new ViewHolder();
            holder.iconImageView = (ImageView) convertView.findViewById(R.id.icon_image_view);
            holder.temperatureLabel = (TextView) convertView.findViewById(R.id.temperature_label);
            holder.dayLabel = (TextView) convertView.findViewById(R.id.day_name_label);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        Day day = mDays[position];
        holder.iconImageView.setImageResource(day.getIconId());
        holder.temperatureLabel.setText(Double.toString(day.getTemperatureMax()));

        if(position == 0) {
            holder.dayLabel.setText("Today");
        } else {
            holder.dayLabel.setText(day.getDayOfWeek());
        }

        return convertView;
    }

This is the line you are missing: ViewHolder holder; You get a null pointer because the first time you user holder it has not been declared as an object.

I already have it decorated, just as a member variable instead (force of habit).

Can you double check that in your day.java file you have this function:

 public int getIconId() {
        return Forecast.getIconId(mIcon);
    }

It does indeed have that method. The problem doesn't lie withing loading the list. The list is created just fine with the propper 7 Day forecast...it's whenever I try to scroll the list, I believe it's trying to make a new list item out of nothing, and getting that NullPointer exception.

if I remember the video correctly, the line that replaces the view item when scrolled is this:

holder = (ViewHolder) convertView.getTag();

can you set a break point on the line that is causing the issue and find out which variable is giving the null pointer?

jason phillips -- The holder itself yields "null", and holder.iconImageView ... holder.tempLabel ... and holder.dayLabel all cause the NullPointerExceptions.

oh i think i found it:

if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(R.layout.daily_list_item, null);
            holder = new ViewHolder();
            holder.iconImageView = (ImageView) convertView.findViewById(R.id.iconImageView);
            holder.tempLabel = (TextView) convertView.findViewById(R.id.tempLabel);
            holder.dayLabel = (TextView) convertView.findViewById(R.id.dayNameLabel);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

in this block before the else you need to add this:

convertView.setTag(holder);

it should look like this:

if(convertView == null) {
            convertView = LayoutInflater.from(mContxt).inflate(R.layout.daily_list_item, null);
            holder = new ViewHolder();
            holder.iconImageView = (ImageView) convertView.findViewById(R.id.icon_image_view);
            holder.temperatureLabel = (TextView) convertView.findViewById(R.id.temperature_label);
            holder.dayLabel = (TextView) convertView.findViewById(R.id.day_name_label);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

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