如何使适配器不 return convertView？

Question

我有一个扩展 ArrayAdapter 的适配器。我给适配器一个 ArrayList，例如，有 9 个对象，我希望它不在 ListView 中显示第五个对象。

有办法吗？我尝试在返回之前设置 convertView = null 但它抛出 NullPointerException.

这是相关代码，它使视图不接受值，但无论如何都会将其添加到列表视图中：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Switch;
import android.widget.TextView;
import android.widget.Toast;


/*@SuppressLint("ViewHolder") */public class AdapterActions extends ArrayAdapter<Action>{

    // our ViewHolder.
    // caches our TextView
    static class ViewHolderItem {
        TextView codigo;
        TextView accion;
        TextView evento;
        Switch UnSwitch;
        boolean isChecked1;
    }

    Activity context;
    ArrayList<Action> listaActions;
    @SuppressLint("UseSparseArrays") Map <Integer, Boolean> map = new HashMap<Integer, Boolean>();

    // Le pasamos al constructor el contexto y la lista de contactos
    public AdapterActions(Activity context, ArrayList<Action> listaActions) {
        super(context, R.layout.layout_adapter_actions, listaActions);
        this.context = context;
        this.listaActions = listaActions;




    }

    public View getView(final int position, View convertView, ViewGroup parent) {

        ViewHolderItem viewHolder;

        // Rescatamos cada item del listview y lo inflamos con nuestro layout
        //View item = convertView;
        //item = context.getLayoutInflater().inflate(R.layout.layout_adapter_actions, null);
        // well set up the ViewHolder
        viewHolder = new ViewHolderItem();

        if(convertView==null){

            // inflate the layout
            LayoutInflater inflater = ((Activity) context).getLayoutInflater();
            convertView = inflater.inflate(R.layout.layout_adapter_actions, parent, false);

            // well set up the ViewHolder
            viewHolder.codigo = (TextView) convertView.findViewById(R.id.codigo);
            viewHolder.accion = (TextView) convertView.findViewById(R.id.accion);
            viewHolder.evento = (TextView) convertView.findViewById(R.id.evento);
            viewHolder.UnSwitch = (Switch) convertView.findViewById(R.id.activa);
            convertView.setLongClickable(true);

            // store the holder with the view.
            convertView.setTag(viewHolder);

        }else{
            // we've just avoided calling findViewById() on resource everytime
            // just use the viewHolder
            viewHolder = (ViewHolderItem) convertView.getTag();
        }

        Action a = new Action(-99, 1, 1, true);
        AccionDefinida LaAccion = new AccionDefinida(0, 0, "", "");
        EventoDefinido ElEvento = new EventoDefinido(0, 0, "", "");

        //ACTIONS
                ActionsSQLite base = new ActionsSQLite(context, "Actions", null,1);
                SQLiteDatabase db1 = base.getReadableDatabase();
                db1 = context.openOrCreateDatabase("Actions",SQLiteDatabase.OPEN_READONLY, null);

                String query = "SELECT * FROM Actions WHERE Id = " + String.valueOf(position + 1);
                Cursor c1 = db1.rawQuery(query, null);

                try{
                    if(c1!=null){

                        int i = c1.getColumnIndexOrThrow("Id");
                        int j = c1.getColumnIndexOrThrow("IdAccionDefinida");
                        int k = c1.getColumnIndexOrThrow("IdEventoDefinido");
                        int l = c1.getColumnIndexOrThrow("Activa");
                        boolean esActiva;

                        //Nos aseguramos de que existe al menos un registro
                        while(c1.moveToNext()){
                            if (c1.getInt(l) == 0){
                                esActiva = false;
                            } else
                            {
                                esActiva = true;
                            }
                            //Recorremos el cursor hasta que no haya más registros
                            a = new Action(c1.getInt(i), c1.getInt(j), c1.getInt(k), esActiva);
                        }
                    }
                    else 
                        Toast.makeText(context.getApplicationContext(), 
                                  "No hay nada :(", Toast.LENGTH_LONG).show();
                  }
                  catch (Exception e){
                    Log.i("bdActions", "Error al abrir o crear la base de datos" + e); 
                  }

                  if(db1!=null){
                        db1.close();
                }   

        if(a.getId() != -99)
        {
        //EVENTOS
        EventosDefinidosSQLite base2 = new EventosDefinidosSQLite(this.context, "EventosDefinidos", null, 1);
        SQLiteDatabase db2 = base2.getReadableDatabase();
        db2 = context.openOrCreateDatabase("EventosDefinidos",SQLiteDatabase.OPEN_READONLY, null);

        String query2 = "SELECT * FROM EventosDefinidos WHERE Id = " + a.getIdEventoDefinido();
        Cursor c2 = db2.rawQuery(query2, null);
        try{
            if(c2!=null){

                int h = c2.getColumnIndexOrThrow("Id");
                int k = c2.getColumnIndexOrThrow("IdEvento");
                int i = c2.getColumnIndexOrThrow("Nombre");
                int j = c2.getColumnIndexOrThrow("Aux");

                //Nos aseguramos de que existe al menos un registro
                while(c2.moveToNext()){
                    //Recorremos el cursor hasta que no haya más registros
                    ElEvento = new EventoDefinido(c2.getInt(h), c2.getInt(k), c2.getString(i), c2.getString(j));
                }
            }
            else 
                Toast.makeText(context.getApplicationContext(), 
                      "No hay nada :(", Toast.LENGTH_LONG).show();
        }
        catch (Exception e){
            Log.i("bdEventos", "Error al abrir o crear la base de datos" + e); 
        }

        if(db2!=null){
            db2.close();
        }   
        //ACCIONES
        AccionesDefinidasSQLite base3 = new AccionesDefinidasSQLite(context, "AccionesDefinidas", null,1);
        SQLiteDatabase db3 = base3.getReadableDatabase();
        db3 = context.openOrCreateDatabase("AccionesDefinidas", SQLiteDatabase.OPEN_READONLY, null);

        String query3 = "SELECT * FROM AccionesDefinidas WHERE Id = " + String.valueOf(a.getIdAccionDefinida());
        Cursor c3 = db3.rawQuery(query3, null);
        try{
            if(c3!=null){

                int h = c3.getColumnIndexOrThrow("Id");
                int k = c3.getColumnIndexOrThrow("IdAccion");
                int i = c3.getColumnIndexOrThrow("Nombre");
                int j = c3.getColumnIndexOrThrow("Aux");

                //Nos aseguramos de que existe al menos un registro
                while(c3.moveToNext()){
                    //Recorremos el cursor hasta que no haya más registros
                    LaAccion = new AccionDefinida(c3.getInt(h), c3.getInt(k), c3.getString(i), c3.getString(j));
                }
            }
            else 
                Toast.makeText(context.getApplicationContext(), 
                      "No hay nada :(", Toast.LENGTH_LONG).show();
        }
        catch (Exception e){
            Log.i("bdAcciones", "Error al abrir o crear la base de datos" + e); 
        }

        if(db3!=null){
            db3.close();
        }

        // object item based on the position


        // assign values if the object is not null
        if(a != null) {
            // get the TextView from the ViewHolder and then set the text (item name) and tag (item ID) values
            viewHolder.codigo.setText(String.valueOf(a.getId()));
            viewHolder.codigo.setTag(a.getId());
            viewHolder.accion.setText(LaAccion.getNombre());
            viewHolder.evento.setText(ElEvento.getNombre());
            viewHolder.UnSwitch.setChecked(a.getActiva());
            Log.e("Position+1: "+ String.valueOf(position+1), "Id: "+ String.valueOf(a.getId()));


        }

        viewHolder.isChecked1 = viewHolder.UnSwitch.isChecked();
        map.put(position, viewHolder.isChecked1);
        viewHolder.UnSwitch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.e("OnClick", "Se clickeó");

                listaActions.get(position).setActiva(map.get(position));
                Log.e("Listener del switch", "Modificó la action en la lista de la ActividadPrincipal");
                int isActiva;
                if(map.get(position) == true)
                {
                    isActiva = 0;
                    Log.e("Listener del switch", "isActiva = 1");
                    map.put(position, false);
                } else
                {
                    isActiva = 1;
                    Log.e("Listener del switch", "isActiva = 0");
                    map.put(position, true);
                }
                String query = "UPDATE Actions SET Activa = " + String.valueOf(isActiva) + " WHERE Id = " + String.valueOf(position+1);
                Log.e("Consulta:", query);
                Log.e("Listener del switch", "query creado");
                Log.e("La position debería ser", String.valueOf(position+1));
                Log.e("Y el valor del map.get(position) es", String.valueOf(map.get(position)));
                ActionsSQLite helper1  = new ActionsSQLite(context, "Actions", null, 1);
                Log.e("Listener del switch", "Creo el helper");
                SQLiteDatabase db = helper1.getWritableDatabase();
                Log.e("Listener del switch", "obtenida la base escribible");
                db.execSQL(query);
                Log.e("Listener del switch", "Query ejecutado");
            }
        });
        } else
        {
            convertView = null;
        }


        return convertView;


    }
}

Answer 1

一旦您告诉 ArrayAdapter 您有（例如）9 个项目，那么您的 getView 函数需要能够为所有 9 个项目创建视图。如果您实际上不希望这些项目之一显示在适配器中，则需要将其从适配器中删除，这样 Android 就不会调用 getView 来显示该项目。

有几种方法可以解决这个问题。最简单的方法是像您目前正在做的那样构造您的适配器，然后为您不想包含的操作调用 remove(action)。

另一种选择是覆盖 BaseAdapter 而不是 ArrayAdapter。然后你可以有更复杂的代码来动态地计算出你想要显示多少项目。 BaseAdapter 更灵活，但实现起来仍然很简单。

有道理吗？

如何使适配器不 return convertView？

How to make an Adapter to not return convertView?

android

listview

android-arrayadapter

convertview