java - 在类(而不是 Activity )之间传递数据会导致空指针异常

Question

我有一个 Activity ShowList，其中有一些edittext字段和按钮。我有一个按钮“获取位置”，它通过GPS获取当前位置。

ShowList Activity (工作正常，我可以获得位置):

  public class ShowList extends Activity implements OnClickListener{


GPSTracker gps;   //i use GPSTracker to get the location (it is not an activity)
     .........

 case R.id.getlocation:
    // create class object
   gps = new GPSTracker(ShowList.this);

  // check if GPS enabled
 if(gps.canGetLocation()){

          double latitude = gps.getLatitude();
          double longitude = gps.getLongitude();

Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
                    }else{
                        ...
                    }

我有一个自定义适配器:

    public class myAdapter extends BaseAdapter{   
         ShowList locationclass=new ShowList();
         .....
        TextView Location = (TextView) convertView.findViewById(R.id.text_location);

            String lat=Double.toString(locationclass.gps.getLatitude());
            String lo=Double.toString(locationclass.gps.getLongitude());
            String coordinates="Lat: " + lat + "  Long: " + lo;
            Location.setText(coordinates);

我在“String lat...”中收到nullpointer。

那么，如何将 location 从 ShowList Activity 传递到 adapter？

Answer 1

您无法通过new实例化Activity。否则，你应该传递上下文；构造函数中 Adapter 的纬度和经度:

public class myAdapter extends BaseAdapter{   
         private String latitude;
         private String longitude;
         private ArrayList<Item> items;
         private Context context; // TODO: use it for layoutInflater

        //the constructor
        public myAdapter(Context context, ArrayList<myItems> list, String latitude, String longitude) {
            this.items = list;
            this.latitude = latitude;
            this.longitude = longitude;
            this.context = context;
        }
         .....
        TextView Location = (TextView) convertView.findViewById(R.id.text_location);
            String coordinates="Lat: " + this.latitude + "  Long: " + this.longitude;
            Location.setText(coordinates);