Question

 public class WeekAdapter extends ArrayAdapter {

        private int resource;
        private LayoutInflater layoutInflater;
        private String[] week = new String[]{};

        public WeekAdapter(Context context, int resource, String[] objects) {
            super(context, resource, objects);
            this.resource = resource;
            this.week = objects;
            layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder;
            if (convertView == null) {
                holder = new ViewHolder();
                convertView = layoutInflater.inflate(resource, null);
                holder.ivlogo = (LetterImageView) convertView.findViewById(R.id.ivLetter);
                holder.tvWeek = (TextView) convertView.findViewById(R.id.tvmain);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }
            holder.ivlogo.setOval(true);
            holder.ivlogo.setLetter(week[position].charAt(0));
            holder.tvWeek.setText(week[position]);
            return convertView;
        }

        class ViewHolder {
            private LetterImageView ivlogo;
            private TextView tvWeek;

        }
    }

我正在尝试制作时间表。但每当我点击列表时，我的应用程序崩溃了。它说：

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.admin.ttabledemo.Utils.LetterImageView.setOval(boolean)' on a null object reference
        at com.example.admin.ttabledemo.WeekActivity$WeekAdapter.getView(WeekActivity.java:108)

我看过其他类似的问题，但我无法理解错误，因为我已经初始化了持有者对象。

Answer 1

public class WeekAdapter extends ArrayAdapter {

private int resource;
private LayoutInflater layoutInflater;
private String[] week = new String[]{};

public WeekAdapter(Context context, int resource, String[] objects) {
    super(context, resource, objects);
    this.resource = resource;
    this.week = objects;
    layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        holder = new ViewHolder();
        convertView = layoutInflater.inflate(resource, null);

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    holder.ivlogo = (LetterImageView) convertView.findViewById(R.id.ivLetter);
    holder.tvWeek = (TextView) convertView.findViewById(R.id.tvmain);
    holder.ivlogo.setOval(true);
    holder.ivlogo.setLetter(week[position].charAt(0));
    holder.tvWeek.setText(week[position]);
    return convertView;
}

class ViewHolder {
    private LetterImageView ivlogo;
    private TextView tvWeek;

}

}

这样做..（我已将holder.ivlogo和holder.tvweek的分配转移到if-else语句之外。

尝试在空对象引用上调用虚方法

1 个答案: