Question

public class MainActivity extends AppCompatActivity {

ListView lv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lv=(ListView)findViewById(R.id.list_id);
        new JsonTask().execute("https://www.dropbox.com/s/o8yqrfm08wfdh48/Hotels.txt?dl=0");
    }

class JsonTask extends AsyncTask<String,String ,List<MovieModels>>{
    @Override
    protected List<MovieModels> doInBackground(String...Params) {
        HttpURLConnection connection = null;
        BufferedReader reader =  null;

        try {
            URL url = new URL(Params[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            InputStream stream= connection.getInputStream();

            reader=new BufferedReader(new InputStreamReader(stream));
            StringBuffer buffer =new StringBuffer();
            String line="";
            while ((line=reader.readLine())!=null){
                buffer.append(line);

            }
            String finaljson = buffer.toString();

            JSONObject parentObject = new JSONObject(finaljson);
            JSONArray parentArray =parentObject.getJSONArray("Hotels");
            List<MovieModels> modelsList=new ArrayList<>();

            for (int i=0; i<parentArray.length();i++) {
                JSONObject finalobject = parentArray.getJSONObject(i);

                MovieModels models= new MovieModels();
                models.setImage(finalobject.getString("Image"));
                models.setHotel_Name(finalobject.getString("Hotel_Name"));

                modelsList.add(models);

            }

              return modelsList;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }


        return null;
    }

    @Override
    protected void onPostExecute(List<MovieModels> result) {
        super.onPostExecute(result);

        Adapter adapter=new Adapter(getApplicationContext(),R.layout.row,result);
       lv.setAdapter(adapter);

        //to do set the data into list


    }
}

public class Adapter extends ArrayAdapter{

private   List<MovieModels> modelsList;
    private int resource;
  private   LayoutInflater inflater;
    public Adapter(Context context, int resource, List<MovieModels> objects) {
        super(context, resource, objects);
        modelsList= objects;
        this.resource=resource;
        inflater=(LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
    }

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

        if (convertView==null){
            convertView=inflater.inflate(R.layout.row,null);

        }
        ImageView imageView;
        TextView textView;
        imageView=(ImageView)convertView.findViewById(R.id.image_id);
        textView=(TextView)convertView.findViewById(R.id.text_id);

        ImageLoader.getInstance().displayImage(modelsList.get(position).getImage(),imageView);


         textView.setText("Hotel_Name-"+modelsList.get(position).getHotel_Name());

        return convertView;
    }
}}

我在设置适配器类中有错误，有人可以建议吗？

Answer 1

您在null中返回doInBackground，然后将其设置为适配器。

您有2个选项可以解决它：

返回一个空数组，例如return new ArrayList<>();而不是return null 要么检查不要将适配器设置为null。 e.g：

@Override
protected void onPostExecute(List<MovieModels> result) {
    super.onPostExecute(result);
    if (result == null) { 
        //todo handle no result
        return;
    }
    Adapter adapter=new Adapter(getApplicationContext(),R.layout.row,result);
    lv.setAdapter(adapter);

    //to do set the data into list
}

}

编辑：

此外，正如评论中所述，您试图获得的JSON密钥（＆＃34; Hotel_Name＆＃34;）与JSON本身不一样（其＆＃34;酒店名称＆＃34;在JSON中）。修复之后，您将看到列表，尽管它仍然很重要，可以先解决异常。

Answer 2

为您的MovieModels创建一个类：

public class MovieModels(){
    private String imagePath, hotelName;

    public MovieModels(String imagePath, String hotelName){
        this.imagePath = imagePath;
        this.hotelName = hotelName;
    }

    public String getImagePath(){
        return imagePath;
    }

    public String getHotelName(){
        return hotelName;
    }

    public void setImagePath(String imagePath){
        this.imagePath = imagePath;
    }

    public void setHotelName(String hotelName){
        this.hotelName = hotelName;
    }


}

然后像这样修改doInBackground()方法：

@Override
    protected List<MovieModels> doInBackground(String...Params) {
        HttpURLConnection connection = null;
        BufferedReader reader =  null;
        List<MovieModels> modelsList=new ArrayList<>();
        try {
            URL url = new URL(Params[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            InputStream stream= connection.getInputStream();

            reader=new BufferedReader(new InputStreamReader(stream));
            StringBuffer buffer =new StringBuffer();
            String line="";
            while ((line=reader.readLine())!=null){
                buffer.append(line);

            }
            String finaljson = buffer.toString();

            JSONObject parentObject = new JSONObject(finaljson);
            JSONArray parentArray =parentObject.getJSONArray("Hotels");
            for (int i=0; i<parentArray.length();i++) {
                JSONObject finalobject = parentArray.getJSONObject(i);
                String image = finalobject.getString("Image");
                String hotelName = finalobject.getString("Hotel_Name");
                modelsList.add(new MovieModels(image, hotelName));
            }

            return modelsList;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }


        return null;
    }

和你的postExecute()一样：

@Override
protected void onPostExecute(List<MovieModels> result) {
    super.onPostExecute(result);
    if (result == null) { 
        Log.e("MY APPLICATION", "No result to display");
    }
    Adapter adapter=new Adapter(getApplicationContext(),R.layout.row,result);
    lv.setAdapter(adapter);

    //to do set the data into list
}

希望它有所帮助!!!

java.lang.NullPointerException：尝试调用接口方法'int java.util.List.size（）

2 个答案: