AlertDialog can't get context in custom adapter

Question

I'm trying to show a AlertDialog when I press a button from a ViewHolder from my adapter. But when I launch this crash with the next message.

E/AndroidRuntime: FATAL EXCEPTION: main Process: cl.abitsoft.todotick, PID: 4172 android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running? at android.view.ViewRootImpl.setView(ViewRootImpl.java:798)

public class CustomAdapter extends ArrayAdapter<RowModel> implements View.OnClickListener {

    private ArrayList<RowModel> DataSet;
    Context context;

    private static class ViewHolder {
        [...]
    }

    public CustomAdapter(ArrayList<RowModel> data, Context context) {
        super(context, R.layout.list_item_main, data);
        this.DataSet = data;
        this.context = context;
    }

    @Override
    public void onClick(View v) {
        int position = (Integer) v.getTag();
        final Object object = getItem(position);

        switch (v.getId()) {
            case R.id.list_delete_button:
                AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
                builder.show();
                break;
        }
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        [...]
    }

}

EDIT: Added MainActivity.class

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, View.OnClickListener {

    ListView listview;
    private CustomAdapter adapter;

    private Button no, button_accept;
    private EditText edittext_title;
    private Spinner spinner_classes;

    private RowModel rowModel;

    private ArrayList<RowModel> row_models;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(this);

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        // Se inicializan las variables
        edittext_title = findViewById(R.id.main_edittext_title);
        spinner_classes = findViewById(R.id.main_spinner_classes);
        button_accept = findViewById(R.id.main_button_accept);
        listview = findViewById(R.id.main_listview);
        row_models = new ArrayList<>();
        adapter = new CustomAdapter(row_models, getApplicationContext());
        // AL ListView se le asigna el Adapter con el tipo de objeto que usaremos
        listview.setAdapter(adapter);
        // Creamos un arreglo del tipo String con las variables para el Spinner
        String[] values = {"Pagar", "Cobrar", "Llamar", "Pedir", "Comprar", "Revisar", "Otro"};
        // Agregamos las variables a nuestro Spinner
        spinner_classes.setAdapter(new ArrayAdapter<String>(getApplicationContext(), R.layout.spinner_main, values));
        // Habilitamos el click en nuestro boton
        button_accept.setOnClickListener(this);

        loadRows();
    }
    [...]

Answer 1

You will have to use either Activity instance or can TypeCast Context to Activity like this following:

AlertDialog.Builder builder = new AlertDialog.Builder(YourActivity.this);

or

AlertDialog.Builder builder = new AlertDialog.Builder((Activity)context);

and Where you are showing AlertDialog then do something like this

if(!((Activity)context).isFinishing())
{
    builder.show(); 
} 

You will not get that exception

Answer 2

Make this 3 changes to resolve your problem,

1. first pass "this" in CustomAdapter.

   adapter = new CustomAdapter(row_models,this);
   

2. get Activity in CustomAdapter.

   public CustomAdapter(ArrayList<RowModel> data, Activity activity) {
   super(context, R.layout.list_item_main, data);
   this.DataSet = data;
   this.context = context;
   }
   

3. Create AlertDialoge using "activity".

   AlertDialog.Builder builder = new AlertDialog.Builder(activity);
   

Answer 3

Pass the context that you have declared globally

AlertDialog.Builder builder = new AlertDialog.Builder(context);

and change the following line to

adapter = new CustomAdapter(row_models, getApplicationContext());

to

adapter = new CustomAdapter(row_models, this);

I hope this will help.

Answer 4

You can get the Context from your View like this:

@Override public void onClick(View v) { 
    int position = (Integer) v.getTag(); 
    final Object object = getItem(position); 

    switch (v.getId()) { 
        case R.id.list_delete_button: 
            AlertDialog.Builder builder = new AlertDialog.Builder(v.getContext()); 
            builder.show();
            break; 
    } 
}