android - 使用数据库动态更新 Recycler Listview

Question

我看到了所有与我的问题相似的问题(在 this、this、this 和 this 链接中)

我的 Activity 中有 myAdapter.notifyDataSetChanged() 但它不起作用

我有3个类(class)，

• DBHelper - 用于存储和获取数据库内容(这里没有问题)
• SimpleRecyclerAdapter - RecyclerList 的适配器
• 第三 Activity

What i did in ThirdActivity :

I have TextBox to get data and store it in Database and a Button. In the Onclicklistener of Button, i specified code to

• get text from textbox
• add it into table using DBHelper
• retrive data as ArrayList from DBHelper
• myAdapter.notifyDataSetChanged()

当我单击按钮时，我在 LogCat 中获取数据，这是我在 OnclickListener 中指定的，但它未反射(reflect)到 ListView 中。

这是我的代码，

第三 Activity :

public class ThirdActivity extends AppCompatActivity{

    private DrawerLayout mDrawerLayout;
    DbHelper dbHelper;

    EditText et;
    Button addButton;
    RecyclerView rv;
    ArrayList<String> myNotesList;
    SimpleRecycler3Adapter adapter3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.thirdactivity);
        myNotesList = new ArrayList<>();
        et=(EditText) findViewById(R.id.et);
        addButton=(Button)findViewById(R.id.addButton);
        rv = (RecyclerView) findViewById(R.id.dbListrv);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getBaseContext());
        rv.setLayoutManager(linearLayoutManager);
        rv.setHasFixedSize(true);

        adapter3 = new SimpleRecycler3Adapter(myNotesList);
        rv.setAdapter(adapter3);
        dbHelper = new DbHelper(this, null, null, 1);


        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("DB", "Constructor");
              String note=et.getText().toString();
             dbHelper.addNote(note);
               printData();
            }
        });
    }

    public void printData(){
        Log.d("DB","Constructor");
        myNotesList=dbHelper.databasetostring();
        Log.d("DB","Data came"+myNotesList.get(myNotesList.size()-1));
     //  adapter3 = new SimpleRecycler3Adapter(myNotesList);
       // rv.setAdapter(adapter3);
        adapter3.notifyDataSetChanged();
    }
}

简单回收器 View 适配器:

public class SimpleRecycler3Adapter extends RecyclerView.Adapter<SimpleRecycler3Adapter.NotesHolder> {

private  ArrayList<String> myNotesList=new ArrayList<String>();

        String TAG="ThirdAdapter kbt";
        RecyclerView rv;

    public SimpleRecycler3Adapter(ArrayList<String> myList) {
        Log.d(TAG,"Constructor");

            Log.d(TAG,"Not null");
            int i = 0;
            while (i < myNotesList.size()) {
                myNotesList.add(myList.get(i).toString());
            }
            Log.d(TAG,"finish");
    }


    @Override
        public NotesHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
          Log.d(TAG,"On create started");
        View view2 = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.recyclerlist3_item, viewGroup, false);
        Log.d(TAG,"ADAP STAR ONCR second switch 2nd line");
        NotesHolder viewHolder2 = new NotesHolder(view2);
        Log.d(TAG,"ADAP STAR ONCR second switch 3nd line");
        return viewHolder2;
        }

@Override
public void onBindViewHolder(NotesHolder notesHolder, int i) {
        Log.d(TAG, "ONBIND SECOND i value is " + i);


        // notesHolder.thumbnail.setImageResource(R.drawable.placeholder);

        notesHolder.dblistitem.setText(myNotesList.get(i));
          Log.d(TAG,"ONBIND second title issssss");


        }


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

class NotesHolder extends RecyclerView.ViewHolder {

    protected ImageView thumbnail;
    protected TextView dblistitem;
    public NotesHolder(View itemView) {
        super(itemView);
        Log.d(TAG, "JSON Inside HOLDER");
        rv=(RecyclerView)itemView.findViewById(R.id.dbListrv);
      //  thumbnail = (ImageView) itemView.findViewById(R.id.thumbnail);
        dblistitem = (TextView) itemView.findViewById(R.id.dblistitem);


    }

}

}

Answer 1

您不是在更新适配器类中的 myNotesList，而是在 Activity 类中。但是适配器使用它的本地 myNotesList。

因此，在单击按钮时，使用可用的最新数据更新适配器的 myNotesList 并通知适配器。

编辑
将最新数据传递给适配器。在适配器类中有这个方法并在 notifyDataSetChanged() 之前调用它；

public void updateNotes(ArrayList<String> notesList) {
    myNotesList = notesList; 
}