Я могу получить данные, используя Json из API в Asynctask, но проблема в том, когда я использую Recyclerview. Я получил ошибку исключения нулевого указателя. Кто-нибудь может мне помочь?
***MainActivity.java***
private List<Certifications> mCertifications = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.certificationRecyclerview);
new fetchData().execute();
recyclerView.setLayoutManager(new LinearLayoutManager(this));
mAdapter = new GreenAdapter(mCertifications);
recyclerView.setAdapter(mAdapter);
}
}
***GreenAdapter.java***
public class GreenAdapter extends RecycrView.Adapter<GreenAdapter.ViewHolder>{
private Context mContext;
private List<Certifications> mCertifications;
public GreenAdapter(List<Certifications> certifications) {
this.mCertifications = certifications;
}
/** Inner class */
// Stores and recycles views as they are scrolled off screen
public static class ViewHolder extends RecyclerView.ViewHolder {
private TextView certificationTextview;
private TextView meaningTextview;
private TextView orderTextview;
public ViewHolder(@NonNull View itemView) {
super(itemView);
certificationTextview = (TextView) itemView.findViewById(R.id.certificationInfo);
meaningTextview= (TextView) itemView.findViewById(R.id.meaning);
orderTextview = (TextView) itemView.findViewById(R.id.order);
}
}
// Methods
// Usually involves inflating a layout from XML and returning the holder
//Create New Views
@NonNull
@Override
public GreenAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
Context context = parent.getContext();
LayoutInflater inflater = LayoutInflater.from(context);
View certificationView = inflater.inflate(R.layout.certification_list,
parent, false);
//Return a new holder instance
final ViewHolder certificationViewHolder = new ViewHolder(certificationView);
return certificationViewHolder;
}
//binds the data to the Textview in each row
// Involves populatind data into the item through holder
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
// get the data model based on position
Certifications certific = mCertifications.get(position);
//set itemviews based on your views and data model
holder.certificationTextview.setText(certific.getCertification());
holder.meaningTextview.setText(certific.getMeaning());
holder.orderTextview.setText(certific.getOrder());
}
@Override
public int getItemCount() {
return mCertifications.size();
}
**I copied the following from other post**
public void clear(){
mCertifications.clear();
notifyDataSetChanged();
}
public void addAll(List<Certifications> list){
mCertifications.addAll(list);
notifyDataSetChanged();
}
}
***Certifications.java***
public class Certifications{
private String mCertification;
private String mMeaning;
private int mOrder;
public Certifications(String certification,String meaning, int order) {
mCertification = certification;
mMeaning = meaning;
mOrder = order;
} public String getCertification(){
return mCertification;
}
public String getMeaning(){
return mMeaning;
}
public int getOrder(){
return mOrder;
}
}
***FetchData.java***
Public class fetchData extends AsyncTask<String,Void, List<Certifications>> {
private GreenAdapter mGreenAdapter;
// Create an empty ArrayList that we can start adding Certifications to
List<Certifications> mCertifications = new ArrayList<>();;
protected List<Certifications> doInBackground(String... voids) {
try {
URL url = new URL("API");
HttpsURLConnection httpsURLConnection= (HttpsURLConnection) url.openConnection();
InputStream inputStream=httpsURLConnection.getInputStream();
BufferedReader bufferedReader= new BufferedReader(new InputStreamReader(inputStream));
String line = "";
while (line!=null){
line = bufferedReader.readLine();
data = data + line;
}
// Create a JASONObject from the JSON_RESPONSE string
JSONObject root = new JSONObject(data);
JSONObject jsonObject = root.getJSONObject("certifications");
// Извлечь JSONArray, связанный с ключом под названием "US"// который представляет список сертификатов США
JSONArray jsonArray= jsonObject.getJSONArray("US");
for (int i=0; i<jsonArray.length();i++){
JSONObject jasonObject=(JSONObject) jsonArray.get(i);
String cert = jasonObject.getString("certification");
String meaning =jasonObject.getString("meaning");
int order = jasonObject.getInt("order");}
Certifications certification = new Certifications(cert, meaning, order);
mCertifications.add(certification);
}
**Catch code here**
return mCertifications; **Data**
}
@Override
protected void onPostExecute(final List<Certifications> dataParsed) {
// Исключение нулевого указателя для следующего кода при запуске отладки
// Первая попытка. Результат: NullPointerException
mGreenAdapter.clear();
mGreenAdapter.addAll(dataParsed);
// Вторая попытка. Результат: NullPointerException
mGreenAdapter = new GreenAdapter( dataParsed);
mRecyclerView.setAdapter(mGreenAdapter);
}// onPostExecute parenthesis
}// fetchData.java