请帮助我，我错了。我对这个问题感到厌倦。 我有一个类ForcastTask扩展了AsyncTask，另一个类ForcastFragment扩展了Fragment实现的AsyncResponse和Main Activity类。
我想从AsyncTask类获取onPostExcute（List data）并使用AsyncResponse接口发送到ForcastFragment类。
但是它只显示null，我在json viewer online中检查了我的查询参数它是否有效，当我在单个类中尝试它然后它正常工作。
public class ForecastTask extends AsyncTask<String, String, List<MovieModel>> {
private final String LOG_TAG = ForecastTask.class.getSimpleName();
public AsyncResponse delegate=null;
public List<MovieModel> movieModelList=null;
@Override
protected List<MovieModel> doInBackground(String... params) {
if (params.length == 0) {
return null;
}
String Popularity = "http://api.themoviedb.org/3/discover/movie?sort_by=popularity.desc&api_key=XXXXXxxxxxxxxxxxxx";
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(Popularity);
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.connect();
InputStream inputStream = connection.getInputStream();
if (inputStream == null) {
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
StringBuffer buffer = new StringBuffer();
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
JSONObject jsonObject = new JSONObject(buffer.toString());
JSONArray jsonArray = jsonObject.getJSONArray("results");
//adding JSON Array data into MovieModel Class
movieModelList = new ArrayList<>();
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject finalObject = jsonArray.getJSONObject(i);
MovieModel movieModel = new MovieModel();
movieModel.setId(finalObject.getInt("id"));
movieModel.setTitle(finalObject.getString("title"));
movieModel.setPoster_path(finalObject.getString("poster_path"));
movieModel.setRelease_date(finalObject.getString("release_date"));
movieModel.setVote_average((float) finalObject.getDouble("vote_average"));
movieModel.setOverview(finalObject.getString("overview"));
movieModelList.add(movieModel);
}
return movieModelList;
} catch (JSONException | IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(List<MovieModel> movieModels) {
delegate.processFinish(movieModels);
}
}
2- ForecastFragment类
public class ForecastFragment extends Fragment implements AsyncResponse{
private List<MovieModel> movieModelList=null;
private static final String STATE_MOVIES ="state_movies";
private CustomAdapter customAdapter =null;
private GridView gridView=null;
private View rootView=null;
ForecastTask forecastTask=new ForecastTask();
//Constructor
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
forecastTask.delegate=this;
forecastTask.execute("Popular");
}
@Override
public void processFinish(List<MovieModel> movieModels) {
movieModelList=movieModels;
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putParcelableArrayList(STATE_MOVIES, (ArrayList<? extends Parcelable>) movieModelList);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
super.onCreateOptionsMenu(menu, inflater);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()){
case R.id.most_Popular:
if(item.isChecked()){
item.setChecked(false);
}else{
item.setChecked(true);
new ForecastTask().execute("Popular");
return true;
}
case R.id.High_rated:
if(item.isChecked()){
item.setChecked(false);
}else{
item.setChecked(true);
new ForecastTask().execute("TOP_RATED");
return true;
}
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.activity_main, container, false);
customAdapter= new CustomAdapter(
getActivity(),
R.layout.list_image_forecast,
movieModelList);
gridView=(GridView)rootView.findViewById(R.id.gridView);
if (movieModelList==null){
Toast.makeText(getActivity(),"Null",Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(getActivity(), "Data", Toast.LENGTH_SHORT).show();
gridView.setAdapter(customAdapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String movie_name = movieModelList.get(position).getTitle();
String poster_path = movieModelList.get(position).getPoster_path();
String release_date = movieModelList.get(position).getRelease_date();
Float users_rating = movieModelList.get(position).getVote_average();
String overview = movieModelList.get(position).getOverview();
Intent intent = new Intent(getActivity(), DetailActivity.class)
.putExtra("movie_Name", movie_name)
.putExtra("poster_Path", poster_path)
.putExtra("release_Date", release_date)
.putExtra("users_Rating", users_rating)
.putExtra("overview", overview);
startActivity(intent);
}
});
}
return rootView;
}
}
3-异步接口
public interface AsyncResponse {
void processFinish(List<MovieModel> movieModels);
}
4-Movie DB
public class MovieModel implements Parcelable {
private int id;
private String title;
private String poster_path;
private String release_date;
private float vote_average;
private String overview;
private List<MovieModel> models;
public MovieModel(){
}
public List<MovieModel> getModels() {
return models;
}
public void setModels(List<MovieModel> models) {
this.models = models;
}
public MovieModel(int id, String title, String poster_path, String release_date, float vote_average, String overview) {
this.id = id;
this.title = title;
this.poster_path = poster_path;
this.release_date = release_date;
this.vote_average = vote_average;
this.overview = overview;
}
protected MovieModel(Parcel in) {
id = in.readInt();
title = in.readString();
poster_path = in.readString();
release_date = in.readString();
vote_average = in.readFloat();
overview = in.readString();
}
public static final Creator<MovieModel> CREATOR = new Creator<MovieModel>() {
@Override
public MovieModel createFromParcel(Parcel in) {
return new MovieModel(in);
}
@Override
public MovieModel[] newArray(int size) {
return new MovieModel[size];
}
};
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getPoster_path() {
return poster_path;
}
public void setPoster_path(String poster_path) {
this.poster_path = poster_path;
}
public String getRelease_date() {
return release_date;
}
public void setRelease_date(String release_date) {
this.release_date = release_date;
}
public float getVote_average() {
return vote_average;
}
public void setVote_average(float vote_average) {
this.vote_average = vote_average;
}
public String getOverview() {
return overview;
}
public void setOverview(String overview) {
this.overview = overview;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel out, int flags) {
out.writeInt(id);
out.writeString(title);
out.writeString(poster_path);
out.writeString(release_date);
out.writeFloat(vote_average);
out.writeString(overview);
}
}
5-主要活动
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// Call the ForecastFragment Class by getFragmentManager
getFragmentManager()
.beginTransaction()
.add(R.id.Fragment_Container, new ForecastFragment(),
ForecastTask.class.getSimpleName())
.commit();
}
答案 0 :(得分：0)
您只是在定义为片段成员的delegate中分配forecastTask一次。但是，您可以在其他位置创建多个任务，而无需分配其委托。您可能需要为每个任务分别为每个任务分配委托以在onPostExecute中进行更改，否则它将因NullPointerException而崩溃。
答案 1 :(得分：0)
我建议你将AsyncResponse的一个对象传递给ForecastTask构造函数。
public ForecastTask(AsyncResponse listener){
delegate = listener;
}
在您的片段中，您可以执行此操作。
ForecastTask forecastTask = new ForecastTask(this);
forecastTask.execute("Popular");