将回收器视图限制为特定数量的子视图并在滚动到底部时加载

Question

我的 sqlite db(android) 中存储了近 100-120 个数据。 我已经将数据提取到回收器视图并显示在布局中，但是我怎样才能使回收器视图从数据库中仅加载 20 条数据，并且当页面滚动到底部时，它再次获取接下来的 20 个项目并附加它与 20 项并显示 40 项，直到所有数据加载完成。

这是我的代码。

public class MainActivity extends AppCompatActivity {
RecyclerView recycler;
private LinearLayoutManager mLayoutManager;
private BranchAdapter mAdapter;
private  static MyDatabase db;
private static SQLiteDatabase sdb;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    recycler= (RecyclerView)findViewById(R.id.maiinRecycler);
    db= new MyDatabase(this);
    sdb= db.getWritableDatabase();
    mLayoutManager= new LinearLayoutManager(getApplicationContext());
    recycler.setLayoutManager(mLayoutManager);
    mAdapter = new BranchAdapter(getApplicationContext(),Branch.getdata());
    recycler.setAdapter(mAdapter);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main_menu, menu);
    final MenuItem searchItem = menu.findItem(R.id.action_search);
    SearchView search = (SearchView) MenuItemCompat.getActionView(searchItem);
    search.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {
            return false;
        }

        @Override
        public boolean onQueryTextChange(String newText)
        {
            return false;
        }
    });
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement

    return super.onOptionsItemSelected(item);
}

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


    private Context context;

    private ArrayList<BranchInformation> branch;

    private LayoutInflater inflater;
    String Name;


    public BranchAdapter(Context context, ArrayList<BranchInformation> branch) {
        this.context = context;
        this.branch = branch;
        // inflater = LayoutInflater.from(context);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int position) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.main_card, parent, false);
        MyViewHolder holder = new MyViewHolder(view);

        return holder;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder myViewHolder, final int position) {

        final TextView Title= (TextView)myViewHolder.view.findViewById(R.id.titleText);
        final TextView Pledge= (TextView)myViewHolder.view.findViewById(R.id.pledgedText);
        final TextView Backers= (TextView)myViewHolder.view.findViewById(R.id.backersText);
       // final LinearLayout BranchLayout =(LinearLayout)myViewHolder.view.findViewById(R.id.BranchL);
        Title.setText(branch.get(position).Title);
        Pledge.setText("Pleadge: "+branch.get(position).Pledge+" "+branch.get(position).Currency);
        Backers.setText("Backers: "+branch.get(position).Backers);


    }

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

    class MyViewHolder extends RecyclerView.ViewHolder {
        public View view;
        public MyViewHolder(View itemView) {
            super(itemView);
            view =itemView;
        }


    }
    // This method adds(duplicates) a Object (item ) to our Branch set as well as Recycler View.
}

public static class Branch {

    public static ArrayList<BranchInformation> getdata() {
        ArrayList<BranchInformation> branch = new ArrayList<BranchInformation>();
        // Select All Query
        try {
            String selectQuery = "SELECT title, amtpledged, numbackers, currency FROM data";
            sdb = db.getWritableDatabase();

            Cursor cursor = sdb.rawQuery(selectQuery, null);
            // looping through all rows and adding to list
            if (cursor.moveToFirst()) {
                do {
                    BranchInformation current = new BranchInformation();
                    current.Title=cursor.getString(0);
                    current.Pledge= cursor.getString(1);
                    current.Backers= cursor.getString(2);
                    current.Currency= cursor.getString(3);
                    branch.add(current);
                } while (cursor.moveToNext());
            }
        }catch (Exception e) {
            //    Toast.makeText(,"Error Finding data. Please sync to Update Data.", Toast.LENGTH_SHORT).show();}
        }

        // return contact list
        return branch;
    }
}

public static class BranchInformation {
    public String Title;
    public String Pledge;
    public String Backers;
    public String Currency;


}

}

Answer 1

这称为分页。

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


private Context context;

private ArrayList<BranchInformation> branch;

private LayoutInflater inflater;
String Name;


public BranchAdapter(Context context, ArrayList<BranchInformation> branch) {
    this.context = context;
    this.branch = branch;
    // inflater = LayoutInflater.from(context);
}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int position) {

    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.main_card, parent, false);
    MyViewHolder holder = new MyViewHolder(view);

    return holder;
}

@Override
public void onBindViewHolder(final MyViewHolder myViewHolder, final int position) {

    final TextView Title= (TextView)myViewHolder.view.findViewById(R.id.titleText);
    final TextView Pledge= (TextView)myViewHolder.view.findViewById(R.id.pledgedText);
    final TextView Backers= (TextView)myViewHolder.view.findViewById(R.id.backersText);
   // final LinearLayout BranchLayout =(LinearLayout)myViewHolder.view.findViewById(R.id.BranchL);
    Title.setText(branch.get(position).Title);
    Pledge.setText("Pleadge: "+branch.get(position).Pledge+" "+branch.get(position).Currency);
    Backers.setText("Backers: "+branch.get(position).Backers);


}

public void updateList(ArrayList<BranchInformation> list){
   int beforeInsertSize = branch.size();
   branch.addAll(list)
   notifyItemRangeInserted(beforeInsertSize,list.size);
}

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

class MyViewHolder extends RecyclerView.ViewHolder {
    public View view;
    public MyViewHolder(View itemView) {
        super(itemView);
        view =itemView;
    }


}
}

public class MainActivity extends AppCompatActivity {
RecyclerView recycler;
private LinearLayoutManager mLayoutManager;
private BranchAdapter mAdapter;
private  static MyDatabase db;
private static SQLiteDatabase sdb;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   recycler= (RecyclerView)findViewById(R.id.maiinRecycler);
   db= new MyDatabase(this);
   sdb= db.getWritableDatabase();
   mLayoutManager= new LinearLayoutManager(getApplicationContext());
   recycler.setLayoutManager(mLayoutManager);
   mAdapter = new 
   BranchAdapter(getApplicationContext(),Branch.getdata());
   recycler.setAdapter(mAdapter);
   recycler.addOnScrollListener(mScrollListener);

}

  RecyclerView.OnScrollListener mScrollListener = new 
  RecyclerView.OnScrollListener() {
    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) 
   {

        int visibleItemCount = gridLayoutManager.getChildCount();
        int totalItemCount = gridLayoutManager.getItemCount();
        int pastVisibleItems = gridLayoutManager.findFirstVisibleItemPosition();
        if (pastVisibleItems + visibleItemCount >= totalItemCount) {
            List< BranchInformation > list = Branch.getData();
            mAdapter.updateList(list);
        }
    }
};
}

您的查询现在会有所不同

int offset; //offset will be the last row number you fetched previously.

//Your query will be something like following. String selectQuery = "SELECT title, amtpledged, numbackers, currency FROM data LIMIT 20 OFFSET "+offset;

Answer 2

您可以编写自己的逻辑来按需加载数据，并使用RecyclerView.OnScrollListener 监听RecyclerView 的滚动事件。

或者使用开源库like this。