为什么 item.getMenuInfo() 返回 null？

Question

I have been trying to make a simple app with a menu that change the bg color of the item that calls the menu. But instead item.getMenuInfo is returning null and I dont know why.

Some solutions on the internet says that it's because you should pass the entire list instead of the items. However I'm passing the entire ListView but I keep getting an java.lang.NullPointerException because item.getMenuItem() returns null.

This is where I register it:

AdaptadorPersonalizado adaptador = new AdaptadorPersonalizado(this, R.layout.layoutlinealistview, elementos);

ListView lista = (ListView) findViewById(R.id.provincias);

lista.setAdapter(adaptador);
lista.setOnItemClickListener(this);

registerForContextMenu(lista);

And is in this method where I use the item.getMenuInfo() function:

public boolean onContextItemSelected(MenuItem item) {
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();

        switch(item.getItemId()) {
            case R.id.rojo:
                return true;

            default:
                return true;
        }
    }

And this is the class where I create the custom ArrayAdapter and assign it the content:

String[] elementos = {"León",
                "Zamora",
                "Salamanca",
                "Palencia",
                "Valladolid",
                "Ávila",
                "Burgos",
                "Segovia",
                "Soria"};

        String[] descripciones = {"Provincia de Leon",
                "Provincia de Zamora",
                "Provincia de Salamanca",
                "Provincia de Palencia",
                "Provincia de Valladolid",
                "Provincia de Ávila",
                "Provincia de Burgos",
                "Provincia de Segovia",
                "Provincia de Soria"
        };

        int[] imagenes = {R.drawable.leon,
                R.drawable.zamora,
                R.drawable.salamanca,
                R.drawable.palencia,
                R.drawable.valladolid,
                R.drawable.avila,
                R.drawable.burgos,
                R.drawable.segovia,
                R.drawable.soria
        };

        class AdaptadorPersonalizado extends ArrayAdapter<String> {
            public AdaptadorPersonalizado(Context ctx, int txtViewResourceId, String[] objects) {
                super(ctx, txtViewResourceId, objects);
            }

            @Override
            public View getDropDownView(int position, View cnvtView, ViewGroup prnt) {
                return crearFilePersonalizada(position, cnvtView, prnt);
            }

            public View getView(int pos, View cnvtView, ViewGroup prnt) {
                return crearFilePersonalizada(pos, cnvtView, prnt);
            }

            private View crearFilePersonalizada(int posicion, View convertView, ViewGroup parent) {
                LayoutInflater inflador = getLayoutInflater();
                View miFila = inflador.inflate(R.layout.layoutlinealistview, parent, false);

                TextView nombre = miFila.findViewById(R.id.textViewNombre);
                nombre.setText(elementos[posicion]);

                TextView descripcion = miFila.findViewById(R.id.textViewDescripcion);
                descripcion.setText(descripciones[posicion]);

                ImageView imagen = miFila.findViewById(R.id.imageViewImagenesCiudades);
                imagen.setImageResource(imagenes[posicion]);

                return miFila;
            }
        }

Thanks in advance.

Answer 1

The Android menu is very easy to use, compared to other widgets like the recycler view. Using an Adapter for a menu is not needed , as it's handled by default. All you need to do is, Create a XML file called menu inside res/layout

<menu xmlns:android="http://schemas.android.com/apk/res/android">
<!-- Single menu item 
     Set id, icon and Title for each menu item -->
     <item android:id="@+id/menu_leon"
      android:icon="@drawable/icon_leon"
      android:title="Leon" />

     <item android:id="@+id/menu_zamora"
      android:icon="@drawable/icon_zamora"
      android:title="zamora" />
  </menu>

For all your menu items, and then Initiate it in your fragment / Activity using

 // Initiating Menu XML file (menu.xml)
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.layout.menu, menu);
        return true;
    }
     

And then do,

     @Override
        public boolean onOptionsItemSelected(MenuItem item)
        {
             
            switch (item.getItemId())
            {
            case R.id.leon:
                //Do your stuff for leon, zomara,etc
                return true;
     }
}

Hope this helped 😇