为什么从片段调用新的活动意图时出错？

Question

试图从适配器调用，但我发现这是更正确的方法。 在“日志”中，一切都传输正确，并且我从适配器调用此方法。 反复尝试更改toContext（），但它也不起作用。

错误在这里：

Process: pl.michalz.hideonscrollexample, PID: 2078
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
    at android.content.ComponentName.<init>(ComponentName.java:128)
    at android.content.Intent.<init>(Intent.java:4449)
    at pl.michalz.hideonscrollexample.fragment.PartThreeFragment.infoActivityCall(PartThreeFragment.java:122)
    at pl.michalz.hideonscrollexample.adapter.parttwo.MyAdapter$ViewHolder.onClick(MyAdapter.java:83)
    at android.view.View.performClick(View.java:5204)
    at android.view.View$PerformClick.run(View.java:21153)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

在此代码中：

public class PartThreeFragment extends Fragment {

    //pridetas
    ArrayList<Receptas> receptasAList = new ArrayList<>();
    MyAdapter myAdapter;
    RecyclerView recyclerView;
    RequestQueue requestQueue;
    Receptas receptas;
    InfoActivity infoActivity = new InfoActivity();
    private final String url1 = "http://smkbaig.esy.es/get_info_test.php";

    public static PartThreeFragment createInstance() {
        PartThreeFragment partThreeFragment = new PartThreeFragment();
        Log.w("myApp", ">>partThree)");
        return partThreeFragment;
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.w("myApp", "partThree>>");
        View view = inflater.inflate(R.layout.fragment_part_three, container, false);
        recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        myAdapter = new MyAdapter(getActivity());
        recyclerView.setAdapter(myAdapter);
        volleyJson(url1, "");

        return view;
    }

    public void volleyJson(String u, String q) {
        String url = "";
        String query = "";
        if(u != ""){
            url = u;
        }
        if(q != ""){
            query = q;
        }

        Log.w("myApp", "volleyJson -started- ");
        requestQueue = Volley.newRequestQueue(this.getActivity());
        JsonObjectRequest jsObjRequest = new JsonObjectRequest
                (Request.Method.GET, url, (String) null, new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            receptasAList.clear();
                            JSONArray ja = response.getJSONArray("receptai");
                            for (int i = 0; i < ja.length(); i++) {

                                JSONObject jsonObject = ja.getJSONObject(i);
                                receptas = new Receptas();
                                receptas.setPav(jsonObject.getString("pav"));
                                //receptas.setApras(jsonObject.getString("apras"));
                                receptas.setIngred_sk(jsonObject.getString("ingred_sk"));
                                receptasAList.add(receptas);
                                Log.w("myApp", "receptasAList.add(receptas); " + receptasAList.get(0).getPav());
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                        //atliekamas po getRecceptas()
                        myAdapter.setReceptasList(receptasAList);
                        Log.w("myApp", "myAdapter.setReceptasList(receptasAList);");
//                         myAdapter.notifyDataSetChanged();
                        //mTextView.setText("Response: " + response.toString());
                    }
                },
                        new Response.ErrorListener() {
                            @Override
                            public void onErrorResponse(VolleyError error) {
                                // TODO Auto-generated method stub
                            }
                        }
                );

        requestQueue.add(jsObjRequest);
        Log.w("myApp", "requestQueue.add(jsObjRequest);");
    }

    public void refresh(String newTxt, Boolean submit){
        final List<Receptas> receptasFilter = myAdapter.filter(receptasAList, newTxt);
        myAdapter.setFilter(receptasFilter, submit, getActivity());
    }

    public void infoActivityCall(int position, Receptas receptas)
    {
        Log.w("myApp", "infoActivityCall return = " + position + " ; " + " re " + receptas.getPav());

        // - - - - - - - - -   E R R O R   H E R E   - - - - - - - - - 

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

}

编辑1：从public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> { ViewHolder类进行调用public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        TextView itemTextViewPav, itemTextViewIngred_sk;
        ArrayList<Receptas> receptasL;
        PartThreeFragment partThreeFragment = new PartThreeFragment();

        public ViewHolder(View itemView, ArrayList<Receptas> receptasL) {
            super(itemView);
            this.receptasL = receptasL;
            itemTextViewPav = (TextView) itemView.findViewById(R.id.itemTextViewPav);
            itemTextViewIngred_sk = (TextView) itemView.findViewById(R.id.itemTextViewIngred_sk);

            // Attach a click listener to the entire row view
            itemView.setOnClickListener(this);
        }

        //- - - - - - - - - - - - - -  C L I C K   L I S T E N E R  - - - - - - - - - - - - - - - -
        // Handles the row being being clicked
        @Override
        public void onClick(View view) {
            int position = getLayoutPosition(); // gets item position
            Receptas receptas = receptasL.get(position);
            // We can access the data within the views

            Toast.makeText(view.getContext(), "Click /VH + ", Toast.LENGTH_SHORT).show();
            partThreeFragment.infoActivityCall(position, receptas);

        }
    }

Answer 1

首先，从片段中打开另一个活动不是一个好习惯，因此，请看一下这种方法来将片段与活动进行通信，然后创建您的意图，例如：

new Intent(ActualClass.this, NewClass.class);

Answer 2

我认为错误是在这一行

Volley.newRequestQueue(this.getActivity());

所以我可以建议您创建一个类型为Activity的全局变量数据，例如

Activity mActivity;

并像这样将当前活动保存在mActivity

@Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        mActivity = activity;
    }

然后进一步每次使用mActivity 。

Answer 3

在ViewHolder的适配器onClick侦听器中，上下文为null，可以放置适配器代码吗？

Answer 4

我想在Activity中调用的函数：

public void infoActivity(Context context){

    Intent intent = new Intent(PartThreeActivity.this, InfoActivity.class);
    startActivity(intent);
}

在适配器ViewHolder中调用infoActivity() 。

我将mActivity上下文传递给片段myAdapter = new MyAdapter(mActivity); ：

正如@Shree Krishnam所写，我将活动保存为全局变量数据类型：

@Override
public void onAttach(Activity activity){
    super.onAttach(activity);
    mActivity = activity;
}

在适配器中，我保存了它：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    Context context;
    //...code
    public MyAdapter(Context context) {
        layoutInflater = LayoutInflater.from(context);
        this.context = context;
    }
    //...code
}

然后将context传递给ViewHolder并像这样使用它：

public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    //...code...

    @Override
    public void onClick(View view) {
        //...code
        ((PartThreeActivity)context).infoActivity(context);

    }
}