What is a promise in Javascript?

Question

Enrique Espinosa

Asked: 2020-12-01 10:54:45 +0800 CST 2020-12-01 10:54:45 +0800 CST 2020-12-01 10:54:45 +0800 CST

错误：空对象引用上的 android.content.Context.getPackageName()'

772

我正在尝试执行 Intent，但是在启动 Intent 时它给了我一个错误，它向我显示以下错误：

尝试在空对象引用上调用虚拟方法“java.lang.String android.content.Context.getPackageName()”

我不知道为什么当我调用我的意图时会发生此错误，这是我尝试执行我的意图的方法：

public void vistaDetalle(String tituloNoticia, String subtituloNoticia, String imagenNoticia, String descripcionNoticia, Context context, Activity activity) {
        Intent intent = new Intent(getContext(), DescripcionNoticias.class);
        intent.putExtra("titulon",tituloNoticia);
        intent.putExtra("descripcionn", descripcionNoticia);
        intent.putExtra("imagen", imagenNoticia);
        startActivity(intent);
        getActivity().overridePendingTransition(R.anim.left_in, R.anim.left_out);
    }

我已经尝试使用 getActivity() 和其他方法，但没有一个对我有用，这是完整的类：

public class Inicio extends Fragment implements noticiasAdapter.OnEventMovieListener, Response.Listener<JSONObject>, Response.ErrorListener{

    RecyclerView recyclerView;
    private List<Noticias> noticias;
    private noticiasAdapter noticiasadapter;
    public static final String TAG = Noticias.class.getName();

    RequestQueue request;
    JsonObjectRequest jsonObjectRequest;

    Context contextApp;

    public Inicio(){

    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        this.contextApp = context;
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState){
        View view = inflater.inflate(R.layout.inicio, container, false);
        recyclerView = (RecyclerView)view.findViewById(R.id.recycler_view);

        noticias = new ArrayList<>();
        noticiasadapter = new noticiasAdapter(noticias);
        noticiasadapter.setOnEventMovieListener(this);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getContext());
        recyclerView.setLayoutManager(layoutManager);

        request = Volley.newRequestQueue(getActivity());
        cargarWebService();

        return view;
    }

    private void cargarWebService() {

        String url = "http://192.168.1.81:80/webservicemgrex/listaNoticias.php";
        jsonObjectRequest = new JsonObjectRequest(Request.Method.GET,url,null,this,this);
        request.add(jsonObjectRequest);
    }

    @Override
    public void onResponse(JSONObject response) {
        Noticias news = null;
        JSONArray json = response.optJSONArray("inicio");

        try{
            for (int i=0; i<json.length(); i++){
                news = new Noticias();
                JSONObject jsonObject = null;
                jsonObject = json.getJSONObject(i);

                news.setIdNoticia(jsonObject.optInt("idNoticia"));
                news.setTituloNoticia(jsonObject.optString("tituloNoticia"));
                news.setSubtituloNoticia(jsonObject.getString("subtituloNoticia"));
                news.setImagenNoticia(jsonObject.getString("imagenNoticia"));
                news.setDescripcionNoticia(jsonObject.getString("descripcionNoticia"));
                noticias.add(news);
            }

            noticiasAdapter adapter = new noticiasAdapter(noticias);
            recyclerView.setAdapter(adapter);
            noticiasadapter.notifyDataSetChanged();

        }catch (JSONException e){
            Toast.makeText(getActivity(),"Error al cargar la informacion del servidor: "+e, Toast.LENGTH_LONG).show();
            e.printStackTrace();
        }
    }

    @Override
    public void onErrorResponse(VolleyError error) {
        Toast.makeText(getActivity(),"No se pudo consultar los registros: "+error.toString(), Toast.LENGTH_LONG).show();
        Log.i("Error","No se pudo consultar el registro: "+error.toString());
    }

    public void vistaDetalle(String tituloNoticia, String subtituloNoticia, String imagenNoticia, String descripcionNoticia, Context context, Activity activity) {
        Intent intent = new Intent(getContext(), DescripcionNoticias.class);
        intent.putExtra("titulon",tituloNoticia);
        intent.putExtra("descripcionn", descripcionNoticia);
        intent.putExtra("imagen", imagenNoticia);
        startActivity(intent);
        getActivity().overridePendingTransition(R.anim.left_in, R.anim.left_out);
    }


    @Override
    public void onStop() {
        super.onStop();
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

}

这是我调用它的类，当执行 onclick 时，我尝试调用我的 ViewDetail 方法：

public class noticiasAdapter extends RecyclerView.Adapter<noticiasAdapter.NoticiasViewHolder> {

    private List<Noticias> noticias;
    private OnEventMovieListener onEventMovieListener;
    private Context context;
    public Activity activity;

    public interface OnEventMovieListener{
       }

    public class NoticiasViewHolder extends RecyclerView.ViewHolder implements CompoundButton.OnCheckedChangeListener, View.OnClickListener {

        TextView tituloNoticia;
        TextView subtituloNoticia;
        ImageView imagenNoticia;
        TextView descripcionNoticia;
        FloatingActionButton favoritos;
        Button showMore;
        private int contador = 0;

        public NoticiasViewHolder(View itemView){
            super(itemView);

            tituloNoticia = (TextView)itemView.findViewById(R.id.tituloNoticia);
            subtituloNoticia = (TextView)itemView.findViewById(R.id.subtituloNoticia);
            imagenNoticia = (ImageView)itemView.findViewById(R.id.imagenNotica);
            descripcionNoticia = (TextView)itemView.findViewById(R.id.descripcionNoticias);

            favoritos = (FloatingActionButton)itemView.findViewById(R.id.floatingActionButton);
            favoritos.setOnClickListener(this);

            showMore = (Button)itemView.findViewById(R.id.showMore);
            showMore.setOnClickListener(this);

        }

        @Override
        public void onClick(View view) {
            switch(view.getId()){
                case R.id.floatingActionButton:
                    if (contador == 0){
                        favoritos.setImageResource(R.drawable.likedcolor);
                        contador = contador + 1;
                        Noticias fav = noticias.get(getAdapterPosition());
                        noticiasWebService noti = new noticiasWebService();
                        noti.update(fav.getTituloNoticia(), fav.getSubtituloNoticia(), fav.getImagenNoticia(), fav.getDescripcionNoticia(), context);
                        Toast.makeText(context, "Se añadio a tus favoritos ", Toast.LENGTH_LONG).show();
                    }else if (contador == 1){
                        favoritos.setImageResource(R.drawable.unliked);
                        contador = contador - 1;
                        Noticias fav = noticias.get(getAdapterPosition());
                        noticiasWebService noti = new noticiasWebService();
                        noti.deleteRegistro(fav.getTituloNoticia(), context);
                        Toast.makeText(context, "Se elimino de tus favoritos", Toast.LENGTH_LONG).show();

                    }
                    break;
                case R.id.showMore:
                    Noticias news = noticias.get(getAdapterPosition());
                    Inicio inicio = new Inicio();
                    inicio.vistaDetalle(news.getTituloNoticia(), news.getSubtituloNoticia(), news.getImagenNoticia(), news.getDescripcionNoticia(),context, activity );
                    break;
                default:
                    break;
            }
        }

        @Override
        public void onCheckedChanged(CompoundButton compoundButton, boolean b) {

        }
    }

    public noticiasAdapter(List<Noticias> noticias){
        this.noticias = noticias;
    }

    @Override
    public NoticiasViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_noticias, parent, false);
        context = parent.getContext();
        return new NoticiasViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(NoticiasViewHolder holder, int position){

        Noticias news = noticias.get(position);

        holder.tituloNoticia.setText(news.getTituloNoticia());
        holder.subtituloNoticia.setText(news.getSubtituloNoticia());
        final String url = new String(news.getImagenNoticia());
        if(url.isEmpty()){
            Picasso.with(context).load(R.drawable.nofound).into(holder.imagenNoticia);
        }else {
            Picasso.with(context).load(url).into(holder.imagenNoticia);
        }
        holder.descripcionNoticia.setText(news.getDescripcionNoticia());

    }

    @Override
    public int getItemCount(){
        return noticias.size();
    }

    public OnEventMovieListener getOnEventMovieListener() {
        return onEventMovieListener;
    }

    public void setOnEventMovieListener(OnEventMovieListener onEventMovieListener){
        this.onEventMovieListener = onEventMovieListener;
    }
}

这是方法：

 case R.id.showMore:
                    Noticias news = noticias.get(getAdapterPosition());
                    Inicio inicio = new Inicio();
                    inicio.vistaDetalle(news.getTituloNoticia(), news.getSubtituloNoticia(), news.getImagenNoticia(), news.getDescripcionNoticia(),context, activity );
                    break;
                default:
                    break;

这是我试图调用 NewsDescription.class 的类：

公共类 NewsDescription 扩展 AppCompatActivity {

TextView tituloNoticiaDescripcion;
TextView noticiaCompleta;
ImageView imagenNoticiaCompleta;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_descripcion_noticias);

    //Toolbar de la aplicacion en la vista principal
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    toolbar.setTitle("Sección 15");
    toolbar.setSubtitle("Nota completa");

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    String tituloNoticia = getIntent().getExtras().getString("titulon");
    String descripcionNoticia = getIntent().getExtras().getString("descripcionn");
    String imagenNoticia = getIntent().getExtras().getString("imagen");

    tituloNoticiaDescripcion = (TextView)findViewById(R.id.tituloDesNoticia);
    noticiaCompleta = (TextView)findViewById(R.id.noticiaCompleta);
    imagenNoticiaCompleta = (ImageView)findViewById(R.id.imagenNoticiaCompleta);

    tituloNoticiaDescripcion.setText(tituloNoticia);
    noticiaCompleta.setText(descripcionNoticia);
    imagenNoticiaCompleta.setImageResource(R.drawable.noticiauno);

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            overridePendingTransition(R.anim.left_out, R.anim.left_in);
            onBackPressed();
            return true;
    }

    return super.onOptionsItemSelected(item);
}

}

这是完整的错误：

3 Answers

Voted

Jorgesys · Answer 1 · 2020-12-01T17:34:20+08:00

Jorgesys

2020-12-01T17:34:20+08:002020-12-01T17:34:20+08:00

从片段开始活动。

如果你想从一个 Fragment 中打开一个 Activity，你必须使用 as context getActivity()，这样你就可以得到包含这个 Fragment 的 Activity 的上下文。

例子：

  Intent intent = new Intent(getActivity(), DescripcionNoticias.class);
  startActivity(intent);

  //*Incorrecto.
  //Intent intent = new Intent(getContext(), DescripcionNoticias.class);

显然，Activity要启动的必须在您的文件中注册AndroidManifest.xml

如果您在使用它时遇到错误，getActivity()可能是由其他原因引起的，您应该查看该LogCat信息并将该信息添加到您的问题中。

0

Enrique Espinosa · Answer 2 · 2020-12-04T07:46:36+08:00

Best Answer

Enrique Espinosa

2020-12-04T07:46:36+08:002020-12-04T07:46:36+08:00

我已经解决了，我唯一做的就是将方法更改为适配器，然后通过以下方式传递上下文：

我创建一个变量

私有上下文上下文；

在 onCreateViewHolder 方法中，我分配了以下值：

上下文 = parent.getContext();

在我执行意图的方法中，我只传递了contex变量：

case R.id.showMore:
                    Noticias news = noticias.get(getAdapterPosition());
                    Intent intent = new Intent(context, DescripcionNoticias.class);
                    intent.putExtra("titulon",news.getTituloNoticia());
                    intent.putExtra("descripcionn", news.getDescripcionNoticia());
                    intent.putExtra("imagen", news.getImagenNoticia());
                    context.startActivity(intent);
                    break;
                default:

0

Dany · Answer 3 · 2020-12-01T11:01:55+08:00

Dany

2020-12-01T11:01:55+08:002020-12-01T11:01:55+08:00

如果你从片段中投射它，试试这个：

public void vistaDetalle(String tituloNoticia, String subtituloNoticia, String 
imagenNoticia, String descripcionNoticia, Context context, Activity activity) 
{
 try
 {
  Intent intent = new Intent(getActivity(),DescripcionNoticias.class);
  intent.putExtra("titulon",tituloNoticia);
  intent.putExtra("descripcionn", descripcionNoticia);
  intent.putExtra("imagen", imagenNoticia);
  startActivity(intent);
 }
 catch (Exception e) 
 {
 e.printStackTrace();
 }

 }

如果您从 Activity 启动它，它将是：

 Intent intent = new Intent(this, DescripcionNoticias.class);

-3

错误：空对象引用上的 android.content.Context.getPackageName()'

从片段开始活动。

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