> For the complete documentation index, see [llms.txt](https://educacion.gitbook.io/programacion/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://educacion.gitbook.io/programacion/ud5-entrada-e-saida-da-informacion/interfaces-graficas/programacion-orientada-a-eventos.md).

# Programación orientada a eventos

Os eventos son **accións que o usuario realiza ou que acontecen no sistema**, e permiten que a aplicación reaccione.\
En Java Swing, podemos detectar eventos e asociarlles accións mediante *listeners*.

**Exemplos:**

* **ActionEvent** → Un botón foi pulsado (`JButton.addActionListener`).
* **MouseEvent** → O usuario moveu ou clicou co rato (`MouseListener`).
* **KeyEvent** → O usuario presionou unha tecla (`KeyListener`).

{% @mermaid/diagram content="sequenceDiagram
participant Usuario
participant UI as Elemento UI (Botón)
participant Listener
participant App as Aplicación

```
Usuario->>UI: 1. Click/Touch
UI->>Listener: 2. Dispara evento
Listener->>App: 3. Ejecuta callback
App-->>UI: 4. Actualiza interfaz
UI-->>Usuario: 5. Feedback visual" %}
```

## Modelo de xestión de eventos

Cando un usuario interactúa cun compoñente da inteface (por exemplo, premendo un botón, movendo o rato ou pechando unha ventá), producese un evento:

1. O c**ompoñente que que recibe a acción** convirtese na **fonte do evento**
2. Este c**ompoñente fonte, non contén necesariamente o código que debe executarse como resposta,** simplemente detecta que algo aconteceu
3. O **evento xerado transmítese** a un obxecto chamado **listener ou escoitador**
4. O **listener** é o responsable de **reaccionar ante a acción producida**
5. Cando o **evento se produce, o listener recibe un obxecto de clase evento** (ActionEvent, MouseEvent, WindowEvent, KeyEvent,...)
6. O o**bxecto evento conten toda a información** para que o l**istener poida xestionar correctamente a situación**:
   1. Que compoñente xerou o evento
   2. Cando ocorreu o evento
   3. Que tipo de acción concreta se realizou

{% @mermaid/diagram content="classDiagram

```
class CompoñenteUI - ContenedorUI {
    -actionListeners: List~ActionListener~
    -mouseListeners: List~MouseListener~
    +addActionListener(ActionListener)
    +addMouseListener(MouseListener)
    +xerarEvento()
}

class ActionListener {
    <<interface>>
    +actionPerformed(e)
}

class MouseListener {
    <<interface>>
    +mouseClicked(e)
}

CompoñenteUI - ContenedorUI --> "0..*" ActionListener : notifica
CompoñenteUI - ContenedorUI --> "0..*" MouseListener : notifica

class ListenerConcreto {
    +actionPerformed(e)
    +mouseClicked(e)
}

ListenerConcreto ..|> ActionListener
ListenerConcreto ..|> MouseListener" %}
```

## Vantaxes do modelo de eventos

* Basease na separación entre xeración e xestión de eventos
  * O compoñente detecta que algo aconteceu
  * O Listener contén a lóxica da resposta
* A separación facilita a organización do programa e mellora a claridade do códig
* Permite a **modificación do comportamento sen alterar o compoñente gráfico**

## Interfaces Listener mais comúns

| Evento      | Interface Listener | Método de enlace    | Compoñentes típicos |
| ----------- | ------------------ | ------------------- | ------------------- |
| ActionEvent | ActionListener     | addActionListener() | JButton, JTextField |
| MouseEvent  | MouseListener      | addMouseListener()  | Calquera compoñente |
| KeyEvent    | KeyListener        | addKeyListener()    | Campos de texto     |
| WindowEvent | WindowListener     | addWindowListener() | JFrame, JDialog     |

{% hint style="info" %}
**Documentación oficial:** <https://docs.oracle.com/javase/8/docs/api/java/awt/event/ActionListener.html>
{% endhint %}

{% hint style="info" %}
**Documentación oficial:** <https://docs.oracle.com/javase/8/docs/api/java/awt/event/MouseListener.html>
{% endhint %}

{% hint style="info" %}
**Documentación oficial:** <https://docs.oracle.com/javase/8/docs/api/java/awt/event/KeyEvent.html>
{% endhint %}

{% hint style="info" %}
**Documentación oficial:** <https://docs.oracle.com/javase/8/docs/api/java/awt/event/WindowEvent.html>
{% endhint %}

## Escenario de xestión de eventos e de interfaces

```java
package EventosBasico;

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.LocalDateTime;

public class PanelPersonalizado extends JPanel {

    private JButton botonEjemplo;

    public PanelPersonalizado(){
        this.botonEjemplo = new JButton("Boton de ejemplo");
        this.botonEjemplo.setEnabled(true);
        this.add(botonEjemplo);

        this.botonEjemplo.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("El boton acaba de ser pulsado " + LocalDateTime.now());
            }
        });
    }

    public JButton getBotonEjemplo() {
        return botonEjemplo;
    }
}

```

```java
package EventosBasico;

import javax.swing.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

public class FramePersonalizado extends JFrame {

    private PanelPersonalizado panel;

    public FramePersonalizado(){
        this.setTitle("Nuestro Frame Principal");
        this.setSize(600,400);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Añadimos un Listener
        this.addWindowListener(new WindowListener() {
            @Override
            public void windowOpened(WindowEvent e) {
                System.out.println("Acaba de abrirse la ventana");
            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("Acaba de cerrarse la ventana");
            }

            @Override
            public void windowClosed(WindowEvent e) {

            }

            @Override
            public void windowIconified(WindowEvent e) {

            }

            @Override
            public void windowDeiconified(WindowEvent e) {

            }

            @Override
            public void windowActivated(WindowEvent e) {

            }

            @Override
            public void windowDeactivated(WindowEvent e) {

            }
        });
        //Iniciamos el Panel
        this.panel = new PanelPersonalizado();
        this.add(panel);
        this.setVisible(true);
    }

    public PanelPersonalizado getPanel() {
        return panel;
    }
}

```

```java
package EventosBasico;

public class App {
    public static void main(String[] args) {
        FramePersonalizado frame = new FramePersonalizado();
    }
}
```


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