Java事件监听器及其工作方式

冷不防 2022-12-06 15:39 210阅读 0赞

An event listener in [Java][] is designed to process some kind of event — it "listens" for an event, such as a user's mouse click or a key press, and then it responds accordingly. An event listener must be connected to an event object that defines the event.

[Java中][Java]的事件侦听器旨在处理某种事件-它“侦听”事件，例如用户的鼠标单击或按键，然后相应地做出响应。 必须将事件侦听器连接到定义事件的事件对象。

For example, graphical components like a *JButton* or *JTextField* are known as *event sources*. This means that they can generate events (called *event objects*), such as providing a *JButton* for a user to click, or a *JTextField* in which a user can enter text. The event listener's job is to catch those events and do something with them.

例如，诸如*JButton*或*JTextField之*类的图形组件被称为*事件源* 。 这意味着它们可以生成事件(称为*事件对象* )，例如提供供用户单击的*JButton*或用户可以在其中输入文本的*JTextField* 。 事件侦听器的工作是捕获这些事件并对其进行处理。

## 事件监听器如何工作 **(** How Event Listeners Work **)** ##

Each event listener interface includes at least one method used by the equivalent event source.

每个事件侦听器接口都包括至少一个等效事件源使用的方法。

For this discussion, let's consider a mouse event, i.e. anytime a user clicks something with a mouse, represented by the Java class [*MouseEvent*][MouseEvent]. To handle this type of event, you would first create a *MouseListener* class that implements the Java *MouseListener* interface. This interface has five methods; implement the one that relates to the type of mouse action you anticipate your user taking. These are:

在此讨论中，让我们考虑一个鼠标事件，即，用户每次用鼠标单击某些东西时，都由Java类[*MouseEvent表示*][MouseEvent] 。 要处理此类事件，您首先要创建一个实现Java *MouseListener*接口的*MouseListener*类。 该接口有五种方法： 实现与您预期用户将执行的鼠标操作类型有关的操作。 这些是：

*      void mouseClicked(MouseEvent e)
    
    Invoked when the mouse button has been clicked (pressed and released) on a component.
    
    在组件上单击(按下并释放)鼠标按钮时调用。
 *      void mouseEntered(MouseEvent e)
    
    Invoked when the mouse enters a component.
    
    当鼠标进入组件时调用。
 *      void mouseExited(MouseEvent e)
    
    Invoked when the mouse exits a component.
    
    当鼠标退出组件时调用。
 *      void mousePressed(MouseEvent e)
    
    Invoked when a mouse button has been pressed on a component.
    
    在组件上按下鼠标按钮时调用。
 *      void mouseReleased(MouseEvent e)
    
    Invoked when a mouse button has been released on a component
    
    在组件上释放鼠标按钮时调用

As you can see, each method has a single event object parameter: the particular mouse event it is designed to handle. In your *MouseListener* class, you *register* to "listen to" any of these events so that you are informed when they occur.

如您所见，每个方法都有一个事件对象参数：它旨在处理特定的鼠标事件。 在*MouseListener*类中，您*注册*以“监听”这些事件中的任何一个，以便在发生这些事件时得到通知。

When the event fires (for example, the user clicks the mouse, as per the *mouseClicked()* method above), a relevant *MouseEvent* object representing that event is created and passed to the *MouseListener* object registered to receive it.

当事件触发时(例如，用户按照上面的*mouseClicked()*方法单击鼠标)，将创建表示该事件的相关*MouseEvent*对象，并将其传递给注册的*MouseListener*对象以接收该事件。

## 事件监听器的类型 **(** Types of Event Listeners **)** ##

Event listeners are represented by different interfaces, each of which is designed to process an equivalent event.

事件侦听器由不同的接口表示，每个接口旨在处理等效的事件。

Note that event listeners are flexible in that a single listener can be registered to "listen" to multiple types of events. This means that, for a similar set of components that perform the same type of action, one event listener can handle all the events.

请注意，事件侦听器很灵活，因为可以注册单个侦听器以“侦听”多种类型的事件。 这意味着，对于执行相同类型操作的一组相似组件，一个事件侦听器可以处理所有事件。

Here are some of the most common types:

以下是一些最常见的类型：

*  ***ActionListener***: Listens for an *ActionEvent*, i.e. when a graphical element is clicked such as a button or item in a list.
    
    ***ActionListener*** ： ***侦听*** *ActionEvent* ，即单击图形元素(例如按钮或列表中的项目)时。
 *  ***ContainerListener***: Listens for a *ContainerEvent*, which might occur if the user adds or removes an object from the interface.
    
    ***ContainerListener*** ：侦听*ContainerEvent* ，如果用户从接口添加或删除对象，则可能发生。
 *  [***KeyListener***:][KeyListener] Listens for a *KeyEvent* in which the user presses, types or releases a key.
    
    [***KeyListener*** ：][KeyListener]侦听用户在其中按下，键入或释放键的*KeyEvent* 。
 *  ***WindowListener***: Listens for a *WindowEvent*, for example, when a window is closed, activated or deactivated.
    
    ***WindowListener*** ：侦听*WindowEvent* ，例如，在关闭，激活或停用窗口时。
 *  ***MouseListener***: Listens for a  *MouseEvent*, such as when a mouse is clicked or pressed.
    
    ***MouseListener*** ： *侦听MouseEvent* ，例如单击或按下鼠标时。

> 翻译自: [https://www.thoughtco.com/event-listener-2034089][https_www.thoughtco.com_event-listener-2034089]

[Java]: https://www.thoughtco.com/java-programming-4133478
[MouseEvent]: https://www.thoughtco.com/what-is-java-2034117
[KeyListener]: https://www.thoughtco.com/a-keylistener-example-program-2033900
[https_www.thoughtco.com_event-listener-2034089]: https://www.thoughtco.com/event-listener-2034089