使用AsyncTask在片段的RecyclerView中显示json中的数据

Question

我有以下类：

类别Fragment.java

public class CategoryFragment extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "category_name";
// TODO: Rename and change types of parameters
private int mParam1;
public CategoryFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @return A new instance of fragment CategoryFragment.
*/
// TODO: Rename and change types and number of parameters
public static CategoryFragment newInstance(int param1) {
CategoryFragment fragment = new CategoryFragment();
Bundle args = new Bundle();
args.putInt(ARG_PARAM1, param1);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getInt(ARG_PARAM1);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Context context = getActivity();
View view = inflater.inflate(R.layout.listado_noticias, container, false);
RecyclerView rw_noticias = view.findViewById(R.id.rw_noticias);
new LoadArticlesTask().execute(MainScreen.mPrefs,MainScreen.hasRemember,view,context,rw_noticias);

return null;
}
}

listado_noticias.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/constraintLayout"
xmlns:tools="http://schemas.android.com/tools">

<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rw_noticias"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

加载文章任务.java

public class LoadArticlesTask extends AsyncTask<Object, Void, List<Article>> {

private static final String TAG = "LoadArticlesTask";
private View view;
private Context context;
private RecyclerView rw_noticias;
@Override
protected List<Article> doInBackground(Object... params) {
SharedPreferences sp = (SharedPreferences)params[0];
boolean hasRemember = (boolean)params[1];
view = (View)params[2];
context = (Context)params[3];
rw_noticias = (RecyclerView)params[4];
List<Article> res = null;
Properties ini = new Properties();
ini.setProperty(RESTConnection.ATTR_SERVICE_URL,Constants.URL_SERVICE);
ini.setProperty(RESTConnection.ATTR_REQUIRE_SELF_CERT,Constants.CERT_VALUE);
ModelManager.configureConnection(ini);
String strIdUser;
String strApiKey;
String strIdAuthUser;
if(hasRemember){
strIdUser = sp.getString("pref_apikey","");
strApiKey = sp.getString("pref_IdUser","");
strIdAuthUser = sp.getString("pref_strIdAuthUser","");
}else {
strIdUser = ModelManager.getLoggedIdUSer();
strApiKey = ModelManager.getLoggedApiKey();
strIdAuthUser = ModelManager.getLoggedAuthType();
}
//ModelManager uses singleton pattern, connecting once per app execution in enough
if (!ModelManager.isConnected()){
// if it is the first login
if (strIdUser==null || strIdUser.equals("")) {
try {
ModelManager.login(Constants.USER, Constants.PASS);
} catch (AuthenticationError e) {
Log.e(TAG, e.getMessage());
}
}
// if we have saved user credentials from previous connections
else{
ModelManager.stayloggedin(strIdUser,strApiKey,strIdAuthUser);
}
}
//If connection has been successful
if (ModelManager.isConnected()) {
try {
// obtain 6 articles from offset 0
res = ModelManager.getArticles(6, 0);
for (Article article : res) {
// We print articles in Log
Log.i(TAG, String.valueOf(article));
}
} catch (ServerCommunicationError e) {
Log.e(TAG,e.getMessage());
}
}
return res;
}
@Override
protected void onPostExecute(List<Article> articles) {
super.onPostExecute(articles);
Log.i("Articles", articles.toString());
for (Article article : articles) {
// We print articles in Log
Log.i("Articles", String.valueOf(article));
}
refreshList(articles,view);
}
public void refreshList(List<Article> data, View view){
if (data == null){
return;
}
for (Article article : data) {
// We print articles in Log
Log.i("Articles_rl", String.valueOf(article));
}
final LinearLayoutManager layoutManager = new LinearLayoutManager(context);
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
rw_noticias.setLayoutManager(layoutManager);
ArticlesAdapter articlesAdapter = new ArticlesAdapter(data);
rw_noticias.setAdapter(articlesAdapter);
((ArticlesAdapter)rw_noticias.getAdapter()).updateData(data);
}

}

文章适配器.java

public class ArticlesAdapter extends RecyclerView.Adapter<ArticlesAdapter.ArticleViewHolder>{
private List<Article> articulos;
public ArticlesAdapter(List<Article> articulos){
this.articulos = articulos;
}
@NonNull
@Override
public ArticleViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_layout_article, parent, false);
return new ArticleViewHolder(v);
}
@Override
public void onBindViewHolder(@NonNull ArticleViewHolder holder, int position) {
Bitmap imagen = null;
holder.category.setText(articulos.get(position).getCategory());
holder.title.setText(articulos.get(position).getTitleText());
holder.resumen.setText(articulos.get(position).getAbstractText());
try {
imagen = SerializationUtils.base64StringToImg(articulos.get(position).getImage().getImage());
} catch (ServerCommunicationError serverCommunicationError) {
serverCommunicationError.printStackTrace();
}
holder.thumbnail.setImageBitmap(imagen);

}
@Override
public int getItemCount() {
return articulos.size();
}
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
}

public void updateData(List<Article>data){
articulos.clear();
articulos.addAll(data);
notifyDataSetChanged(); //notify to repaint the list
}
public void articlesFilterCategory(String category){
for (Article a : articulos){
if(!category.equals("ALL") && !a.getCategory().equals(category)){
articulos.remove(a);
}
}
}

public static class ArticleViewHolder extends RecyclerView.ViewHolder{
CardView cv;
TextView category;
TextView title;
TextView resumen;
ImageView thumbnail;
public ArticleViewHolder(@NonNull View itemView) {
super(itemView);
cv = (CardView)itemView.findViewById(R.id.card_article);
category = (TextView)itemView.findViewById(R.id.category_noticia);
resumen = (TextView)itemView.findViewById(R.id.resumen_noticia);
thumbnail = (ImageView)itemView.findViewById(R.id.thumbnail);
}
}
}

card_layout_article.xml

<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:foreground="?attr/selectableItemBackground"
android:ellipsize="end"
android:id="@+id/card_article"
>

<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingBottom="16dp"
android:paddingHorizontal="1dp">

<ImageView
android:id="@+id/thumbnail"
android:layout_width="match_parent"
android:layout_height="231dp"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="1dp"
android:layout_marginTop="1dp"
android:adjustViewBounds="true"
android:background="@drawable/a15877171854035"
android:cropToPadding="true"
android:scaleType="fitXY"
android:src="@drawable/degradado" />
<View
android:layout_width="match_parent"
android:layout_height="233dp"
android:background="@drawable/degradado" />
<TextView
android:id="@+id/title_noticia"
android:layout_width="193dp"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/thumbnail"
android:layout_alignParentStart="true"
android:layout_alignParentEnd="true"
android:layout_marginStart="107dp"
android:layout_marginEnd="107dp"
android:layout_marginBottom="95dp"
android:text="Nuevo caso de coronavirus"
android:textAlignment="center"
android:textColor="@color/cardview_light_background"
android:textSize="20dp"
android:textStyle="bold" />
<TextView
android:id="@+id/category_noticia"
android:layout_width="91dp"
android:layout_height="31dp"
android:layout_alignBottom="@+id/thumbnail"
android:layout_alignParentStart="true"
android:layout_alignParentEnd="true"
android:layout_marginStart="11dp"
android:layout_marginEnd="316dp"
android:layout_marginBottom="145dp"
android:text="NATIONAL"
android:textAlignment="center"
android:textColor="@color/cardview_light_background"
android:textSize="15dp"
android:textStyle="bold" />
<TextView
android:id="@+id/resumen_noticia"
android:layout_width="match_parent"
android:layout_height="90dp"
android:layout_alignBottom="@+id/thumbnail"
android:layout_alignParentStart="true"
android:layout_alignParentEnd="true"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:layout_marginBottom="-1dp"
android:text="Nuevo caso de coronavirus"
android:textAlignment="viewStart"
android:textColor="@color/cardview_light_background"
android:textSize="11dp"
android:textStyle="bold" />

</RelativeLayout>
</androidx.cardview.widget.CardView>

在异步任务的Post-Execute中的log.i中，我可以看到文章是如何形成的(Article类有一个toString((函数(。

但我无法在RecyclerView上看到这些文章。我做错了什么？捕获：带有回收器的主屏幕视图为空。。。

谢谢！

Answer 1

像-一样传递RecyclerView的实例

new LoadArticlesTask().execute(MainScreen.mPrefs, MainScreen.hasRemember, view, rw_noticias, context);

在LoadArticlesTask上接收此消息，就像使用View一样。不要在类中重新初始化/使用此代码-

RecyclerView rw_noticias = view.findViewById(R.id.rw_noticias);

Answer 2

在您的card_layout_article.xml中，使cardview的高度为wrap_content：

<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="wrap_content"
........
........

在回收器视图的布局中，而不是ConstraintLayout，尝试使用RelativeLayout作为父级：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/constraintLayout"
xmlns:tools="http://schemas.android.com/tools">

<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rw_noticias"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>