findViewById（）在第二个活动中找不到RecyclerView

Question

我有一个带有RecyclerView（trackingsRecycler）的MainActivity和一个列出CardView的适配器，它可以正常工作。

当我点击某个cardview时，应用程序调用（使用Intent）另一个活动（DetailsActivity），它应该列出另一个RecyclerView（detailsRecycler）。

但在DetailsActivity中的代码

RecyclerView detailsRecyclerView = findViewById(R.id.recycler_details_view);

不起作用

findViewById返回'null'

任何人都可以帮助我吗？

MainActivity.java

public class MainActivity extends AppCompatActivity {

public static final String TRACKING = "com.example.cooltracker.MESSAGE";
private RecyclerView recyclerView;
private TrackingsAdapter adapter;
private List<Tracking> trackingList;
private ProgressDialog pDialog;
private String webserviceURL;
private TextView total;


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

    webserviceURL = "http://myWebServiceUrl.com/params";

    ---> recyclerView = findViewById(R.id.recycler_main_view); <--- Ok!!

    trackingList = new ArrayList<>();
    adapter      = new TrackingsAdapter(this, trackingList);

    total = findViewById(R.id.tvTotal);

    RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 1);
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.addItemDecoration(new GridSpacingItemDecoration(1, dpToPx(5), true));
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(adapter);

    ... 

On TrackingsAdapter.java我把clickListener调用到下一个屏幕

public class TrackingsAdapter extends RecyclerView.Adapter<TrackingsAdapter.MyViewHolder> {

      private Context mContext;
      private List<Tracking> trackingList;

      public class MyViewHolder extends RecyclerView.ViewHolder {...}

      @override
      public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
             View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.tracking_card, parente, attachToRoot:false);
             final MyViewHolder mViewHolder = new MyViewHolder(itemView);

             return new MyViewHolder(itemView);
       }

       @Override
       public void onBindViewHolder(final MyViewHolder...){
             ...
             ...
             ...

             //Here I set the click listener
             holder.card.setOnClickListener(new View.OnClickListener() {

             @Override
             public void onClick(View view) {
                    getDetails(tracking.getTrack());
             }
       });

       private void getDetails(String tracking){

               //Call next screen DetailsActivity...
               Intent intent = new Intent(mContext, DetailsActivity.class);

               intent.putExtra(TRACKING, tracking);

               mContext.startActivity(intent);
       }

到目前为止，它运作良好！代码调用下一个屏幕......

但是...

在下一个屏幕上还应该有一个列表视图（RecyclerView）

DetailsActivity.java

public class DetailsActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private DetailsAdapter adapter;
    private List<Tracking> detailList;
    private ProgressDialog pDialog;
    private String webserviceURL;

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

          //get intent
          Intent intent = getIntent();

          String tracking  = intent.getStringExtra(MainActivity.TRACKING);

          //set string in layout
          TextView tvHeaderLine1 = findViewById(R.id.tvHeaderLine1);
          tvHeaderLine1.setText(tracking);

          webserviceURL = "http://werService.com/otherAction";


          //THIS PART IS NOT WORKING ///
          ----> recyclerView = findViewById(R.id.recycler_detail_view); <----
          System.out.println(recyclerView); // It's always returning NULL

          detailList   = new ArrayList<>();
          adapter      = new DetailsAdapter(this, detailList);

          RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 1);
          //recyclerView.setLayoutManager(mLayoutManager);
          //recyclerView.setAdapter(adapter);

          // prepare the loading Dialog
          pDialog = new ProgressDialog(this);
          pDialog.setMessage("Message");
          pDialog.setCancelable(false);


          ...
          ...

    }

}

Answer 1

解决!!!

首先我想......如果我使用回收商，为什么我需要两个？我应该使用相同的...所以我设置

setContentView(R.layout.activity_main)

在DetailsActivity.class上的

和我使用相同的...谢谢!!!

我现在正在改进设计......

屏幕在这里......我需要至少10个声望才能发布图片... = /

MainActivity Screen

DetailsActivity Screen

谢谢！