在扩展数组适配器时自定义适配器的getView()中的空指针异常
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我试图显示JSON数据,但它给出了空指针异常。它无法获得我正在膨胀的自定义单项的上下文
public class HotelAdapter extends ArrayAdapter{
private List<HotelModel> hotelModelList;
private LayoutInflater layoutInflater;
private int resource;
public HotelAdapter(@NonNull Context context, int resource, @NonNull
List<HotelModel> objects) {
super(context, resource, objects);
hotelModelList = objects;
this.resource=resource;
layoutInflater =
(LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull
ViewGroup parent) {
ViewHolder holder = null;
if (convertView==null){
holder =new ViewHolder();
convertView = layoutInflater.inflate(R.layout.item_hotel,null);
holder.addr =
(TextView)convertView.findViewById(R.id.hotel_add_mini);
holder.categ =
(TextView)convertView.findViewById(R.id.hotel_rating);
holder.name =
(TextView)convertView.findViewById(R.id.hotel_name);
holder.price =
(TextView)convertView.findViewById(R.id.hotel_price);
holder.rating =
(RatingBar)convertView.findViewById(R.id.ratingBar2);
}
else {
holder= (ViewHolder) convertView.getTag();
}
holder.addr.setText(hotelModelList.get(position).getAddr());
holder.categ.setText(hotelModelList.get(position).getCateg());
holder.name.setText(hotelModelList.get(position).getName());
holder.price.setText(Integer.toString(hotelModelList.get(position).getPrice()));
holder.rating.setRating(hotelModelList.get(position).getRating());
return convertView;
}
class ViewHolder{
private ImageView img;
private TextView name;
private TextView addr;
private TextView categ;
private TextView price;
private RatingBar rating;
}
}
它无法从item_hotel.xml布局文件中获取TextView的引用。所以它给出了空指针异常。我检查了List <>,列表是非null因此它只是引用问题。而且,在此
holder.addr =
(TextView)convertView.findViewById(R.id.hotel_add_mini);
(TextView)显示多余,但它不应该具有findViewById返回视图,我们必须将其转换为textView。
答案
您忘记在if条件中设置标记,并且在其他情况下使用标记是问题所在。
在你的if条件中添加,
convertView.setTag(holder);
另一答案
替换这个:
private List<HotelModel> hotelModelList;
private LayoutInflater layoutInflater;
private int resource;
有:
private List<HotelModel> hotelModelList;
private LayoutInflater layoutInflater;
private int resource;
private Context context;
然后更新你的构造函数而不是这个:
public HotelAdapter(@NonNull Context context, int resource, @NonNull
List<HotelModel> objects)
{
super(context, resource, objects);
hotelModelList = objects;
this.resource=resource;
layoutInflater =
(LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
}
使用以下:
public HotelAdapter(@NonNull Context context, int resource, @NonNull
List<HotelModel> objects)
{
super(context, resource, objects);
this.hotelModelList = objects;
this.resource=resource;
this.context = context;
}
之后,而不是以下行:
convertView = layoutInflater.inflate(R.layout.item_hotel,null);
使用以下两行:
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
convertView = inflater.inflate(R.layout.item_hotel, parent, false);
删除以下行:
layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
这将解决您需要为布局inflater提供上下文的问题我认为这可能是您案例中的问题。
另一答案
尝试制作构造函数并设置上下文。
public class HotelAdapter extends ArrayAdapter{
Context mcontext;
private List<HotelModel> mhotelModelList;
public HotelAdapter(Context context, private List<HotelModel> hotelModelList;){
super(context, R.layout.item_hotel, hotelModelList);
this.mcontext = context;
this.mhotelModelList = hotelModelList;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater vi = (LayoutInflater)
mcontext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_hotel, null);
holder = new ViewHolder();
holder.addr =(TextView)convertView.findViewById(R.id.hotel_add_mini);
convertView.setTag(holder);
}
else{
holder = (ViewHolder) convertView.getTag();
holder.addr.setText(hotelModelList.get(position).getAddr());
return convertView;
}
}
另一答案
基本上问题出在这一行
layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
尝试使用你在HotelAdapter
的构造函数中获得的上下文
layoutInflater = (LayoutInflater)context.getSystemService(LAYOUT_INFLATER_SERVICE);
并在convertView上设置标记
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_hotel, null);
holder = new ViewHolder();
holder.addr = (TextView) convertView.findViewById(R.id.hotel_add_mini);
holder.categ = (TextView) convertView.findViewById(R.id.hotel_rating);
holder.name = (TextView) convertView.findViewById(R.id.hotel_name);
holder.price = (TextView) convertView.findViewById(R.id.hotel_price);
holder.rating = (RatingBar) convertView.findViewById(R.id.ratingBar2);
convertView.setTag(holder);
} else{
holder= (ViewHolder) convertView.getTag();
}
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