Fill Jcombobox with an object

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7

I would like a help to fill one JComboBox with a class. In this class, return two parameters: Id and Desc.

Category class I need to show in combo:

private int Id_categoria;
private String Desc_Categoria;

How do I show only the Desc_categoria? And in time to select some value, as I only catch the Id_Categoria?

I’ve tried, pass as parameter in JComboBox an array of category type and also add a model.

java swing jcombobox

  • What have you tried to do? Add to question.

  • How do you get these values? You want to display only one or several values?

  • I receive the values of the database and create an arrayList of categories, I would like to display this list

2 answers

6


Another solution would be to use the comboModel. Simple example:

public class AulaComboModel extends AbstractListModel<Aula> implements ComboBoxModel<Aula> {

    private List<Aula> lista;

    /* Seleciona um objeto na caixa de seleção */
    private Aula selecionado;

    /* Método construtor */
    public AulaComboModel() {
        /* Popula a lista */
        popular();

        /* Define o objeto selecionado */
        setSelectedItem(lista.get(0));
    }

    /* Captura o tamanho da listagem */
    public int getSize() {
        int totalElementos = lista.size();
        return totalElementos;
    }

    /* Captura um elemento da lista em uma posição informada */
    public Aula getElementAt(int indice) {
        Aula t = lista.get(indice);
        return t;
    }

    /* Marca um objeto na lista como selecionado */
    public void setSelectedItem(Object item) {
        selecionado = (Aula) item;
    }

    /* Captura o objeto selecionado da lista */
    public Object getSelectedItem() {
        return selecionado;
    }

    private void popular() {
        try {
            /* Cria o DAO */
            AulaDAO tdao = new AulaDAO();

            /* Cria um modelo vazio */
            Aula t = new Aula();
            t.setNomeUsuario("");

            /* Recupera os registros da tabela */
            lista = tdao.buscar(t);

            /* Cria o primeiro registro da lista */
            Aula primeiro = new Aula();
            primeiro.setIdUsuario(0);
            primeiro.setNomeUsuario("--SELECIONE UM USUARIO--");

            /* Adiciona o primeiro registro a lista */
            lista.add(0, primeiro);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }
}

In that comboModel I retrieve the bank records as follows: lista = tdao.buscar(t);

To implement this comboModel you need to override the method equals and the toString

Do this on the model, example:

 @Override
 public String toString() {
        String texto = idUsuario+" - "+ nomeUsuario;
        return texto;
    }

  @Override
   public boolean equals(Object obj) {
       Aula f = (Aula) obj;
       return Objects.equals(this.idUsuario, f.idUsuario);
   }

Note that in the toString i am concatenating id and name.

If using netbeans go to comboModel component, right-click and go to properties > model > custom code and then install the model created: new AulaComboModel()

inserir a descrição da imagem aqui

This would be a somewhat "bigger" solution to your problem, but the use of comboModel can facilitate and make your code more organized.

inserir a descrição da imagem aqui

  • But the class responsible for displaying the Jcombobox is not the Defaullistcellrenderer?

  • Yes, but the template (fill-in) can be made by AbstractListModel

  • Oh ta, I didn’t even know. I always create a separate model and a different Nderer.

  • I did it that way too, so a friend taught me to do it that way. In the documentation there are some examples as well. https://docs.oracle.com/javase/tutorial/uiswing/components/combobox.html

5

Solution 1

In your custom class, add the method toString() in order to return the parameter Desc_Categoria:

@Override
public String toString()
    return this.Desc_Categoria;
}

Solution 2

You can customize the display of Jcombobox through the method getListCellRendererComponent, class Defaultlistcellrenderer:

DefaultListCellRenderer renderer = new DefaultListCellRenderer() {

            @Override
            public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                  if (value instanceof SuaCustomClasse) {
                    SuaCustomClasse minhaclasse = (SuaCustomClasse) value;
                    setText(minhaclasse.getDesc_Categoria);//supondo que seu parametro seja encapsulado
                }
                return this;
            }

...

   combo.setRenderer(renderer);

This way, you’re changing like the JCombobox displays the elements added to it. You can create a ListCellRenderer customized as well, but it depends on the need and complexity of the objects that will be added to your combobox.

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