Question

每当新项目添加到列表中时，我都会使用Observer类来更新RecyclerView。以下是我的代码 -

Observer<List<StudentEntity>> myObserver = new Observer<List<StudentEntity>>() {
            @Override
            public void onChanged(@Nullable List<StudentEntity> studentEntities) {
                //Update Listview adapter
                lstStudents = studentEntities;
                if (recyclerView.getAdapter()==null){
                    MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener);
                    recyclerView.setAdapter(recyclerViewAdapter);
                }else {
                    //recyclerView.getAdapter().notifyDataSetChanged(); --- This does not work
                    MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener);
                    recyclerView.setAdapter(recyclerViewAdapter);
                    Toast.makeText(getContext(),"New record added",Toast.LENGTH_SHORT).show();

                }
            }
        };

在我使用notifydatasetchanged()时的if条件中，适配器正在重新绘制自己但使用旧数据。但是，当我使用setAdapter方法时，它工作正常。你能解释一下吗？

Answer 1

private void setupRecyclerView() {
    aDummyList.clear();
    aDummyList = MyListUtil.getaDummyList(); //load data or get data from your source

    myAdapter = new MyAdapter(aDummyList);
    myAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
        @Override
        public void onChanged() {
            super.onChanged();
            //  checkAdapterIsEmpty();
            if (layoutManager.getItemCount() == 0) {
                Log.w(TAG, " listSize == 0 ");
                recyclerView.setVisibility(View.GONE);
            } else {
                Log.w(TAG, "  listSize NOT ZERO ");
                recyclerView.setVisibility(View.VISIBLE);
            }
        }
    });

    recyclerView.setAdapter(myAdapter);
    myAdapter.notifyDataSetChanged();
}

这个怎么样！并在onCreate

中设置您的recyclerview配置

noteAdapter = new NoteAdapter(aDummyList, yourContext);
    layoutManager = new LinearLayoutManager(yourContext, LinearLayoutManager.VERTICAL, false);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.addItemDecoration(new DividerItemDecoration(v.getContext(), DividerItemDecoration.VERTICAL));
    recyclerView.setAdapter(noteAdapter);

Answer 2

试试这个

声明您之前的onCreate()方法

MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter;

比使用以下条件

lstStudents.addAll(studentEntities);
if (recyclerViewAdapter==null){
       MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener);
       recyclerView.setAdapter(recyclerViewAdapter);
}else {
      recyclerViewAdapter.notifyItemInserted(arrayList.size());
      recyclerViewAdapter.notifyDataSetChanged();

}

或尝试

声明您之前的onCreate()方法

MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter;
boolean isFtym = true;

比使用以下条件

lstStudents.addAll(studentEntities);
if (isFtym){
       MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener);
       recyclerView.setAdapter(recyclerViewAdapter);
       isFtym = false;
}else {
      recyclerViewAdapter.notifyItemInserted(arrayList.size());
      recyclerViewAdapter.notifyDataSetChanged();

}

Answer 3

MyStudentEntityRecyclerViewAdapter  recyclerViewAdapter;
boolean isAdd= true;


Observer<List<StudentEntity>> myObserver = new Observer<List<StudentEntity>>() {
@Override
public void onChanged(@Nullable List<StudentEntity> studentEntities) {
lstStudents = studentEntities;
recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener);
if (isAdd){
recyclerView.setAdapter(recyclerViewAdapter);
isAdd= false;
}else {
recyclerView.getAdapter().notifyDataSetChanged();
Toast.makeText(getContext(),"New record added",Toast.LENGTH_SHORT).show();
}
}
};

在recyclerViewAdapter中尝试第一个设置列表，然后检查适配器是否为空，如果为null，则使用setAdapter方法，否则使用notifyDataSetChanged方法。

Answer 4

notifyDataSetChanged()顾名思义，只是通知适配器 您已经更新了数据集，因此可以继续重绘

实质上，您必须在通话notifyDataSetChanged()
之前更新数据集
在您的情况下，您的适配器应实现更新方法，如updateStudentList(List<StudentEntity> studentList)

MyStudentEntityRecyclerViewAdapter recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener); Observer<List<StudentEntity>> myObserver = new Observer<List<StudentEntity>>() { @Override public void onChanged(@Nullable List<StudentEntity> studentEntities) { //Update Listview adapter lstStudents = studentEntities; recyclerViewAdapter = new MyStudentEntityRecyclerViewAdapter(lstStudents, mListener); if (recyclerView.getAdapter()!=null){ recyclerView.setAdapter(recyclerViewAdapter); }else { recyclerViewAdapter.updateStudentList(lstStudents); // You should update the students list before you call notifyDataSetChanged() recyclerViewAdapter.notifyDataSetChanged(); Toast.makeText(getContext(),"New record added",Toast.LENGTH_SHORT).show(); } } };

Android RecyclerView set适用，但notifyDatasetchanged（）不在片段中

4 个答案: