我的回收视图不起作用。 你能帮助我吗？

Question

I really need some help. I'm new in android studio. I'm having a problem about my recyclerview, it wont show some items but there's no errors.

Adapter:

public class ClassAdapter extends RecyclerView.Adapter<ClassAdapter.ClassViewHolder> {
       private ArrayList<ExampleClass> qClassList;

       public static class ClassViewHolder extends RecyclerView.ViewHolder {
       public TextView code,name,year;
       public ClassViewHolder(View view){
              super(view);
              code = view.findViewById(R.id.code);
              name = view.findViewById(R.id.name);
              year = view.findViewById(R.id.year);

              }
       }
       public ClassAdapter(ArrayList<ExampleClass> classList){
       qClassList = classList;

       }

       @NonNull
       @Override
       public ClassViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
              View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.activity_classes, viewGroup, false);
              ClassViewHolder cvh = new ClassViewHolder(v);
              return cvh;
       }

       @Override
       public void onBindViewHolder(ClassViewHolder classViewHolder, int i) 
       {
               ExampleClass exampleClass = qClassList.get(i);
               classViewHolder.code.setText(exampleClass.getqCode());
               classViewHolder.name.setText(exampleClass.getqName());
               classViewHolder.year.setText(exampleClass.getqYear());
               }

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

ClassActivity:

     public class ClassActivity extends AppCompatActivity {
     private ArrayList<ExampleClass> exampleClassArrayList;

     private RecyclerView recyclerView;
     private RecyclerView.Adapter adapter;
     private RecyclerView.LayoutManager layoutManager;

     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_classes);
         ArrayList<ExampleClass> exampleClasses = new ArrayList<>();

         exampleClasses.add(new ExampleClass("CANS103","PROGRAMMING 1","BSIT-3"));

         createClassList();
         buildRecycleView();

         FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
         fab.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 // Click action
                 Intent intent = new Intent(ClassActivity.this, CreateClassActivity.class);
                 startActivity(intent);
             }
         });
     }


     public void createClassList(){
         exampleClassArrayList = new ArrayList<>();

     }

     public void buildRecycleView(){
         recyclerView = findViewById(R.id.recyclerView);
         layoutManager = new LinearLayoutManager(this);
         adapter = new ClassAdapter(exampleClassArrayList);
         recyclerView.setLayoutManager(layoutManager);
         recyclerView.setAdapter(adapter);
    }
}

activity_class.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context=".MainActivity">

     <android.support.v7.widget.RecyclerView
         android:id="@+id/recyclerView"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@android:color/darker_gray"
         android:padding="4dp"
         android:scrollbars="vertical"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintHorizontal_bias="0.0"
         app:layout_constraintStart_toStartOf="parent"
         tools:layout_editor_absoluteY="0dp" />

     <android.support.design.widget.FloatingActionButton
         android:id="@+id/fab"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_alignBottom="@+id/recyclerView"
         android:layout_alignParentEnd="true"
         android:layout_marginEnd="27dp"
         android:layout_marginBottom="32dp"
         android:src="@android:drawable/ic_input_add" />

 </RelativeLayout>

I've already search some problems similar to mine but it didn't work. I was wondering if someone can tell me whats the mistake I've done here. I would really appreciate it. Sorry for the inconvience.

Answer 1

在 createClassList() 方法中从您的列表中创建一个新实例，当您在 onCreate 列表中添加一个新项目时，删除调用 createClassList() 工作正常

Answer 2

Chaneg this Lines of code:

 ArrayList<ExampleClass> exampleClasses = new ArrayList<>(); // remove this line No need
          createClassList(); //call this method
         exampleClassArrayList.add(new ExampleClass("CANS103","PROGRAMMING 1","BSIT-3"));

After this call

buildRecycleView()

You are adding in different list (exampleClasses ) and using different list for adapter (exampleClassArrayList) .