为什么 ActionEvent 要求提供 id? [英] Why does ActionEvent ask for an id?

问题描述

在创建 new ActionEvent 时，您需要提供一个整数作为 id.文档说这是:

When making a new ActionEvent, you're required to provide an integer as an id. The documentation says that this is:

标识事件的整数.有关允许值的信息，请参阅 ActionEvent

An integer that identifies the event. For information on allowable values, see the class description for ActionEvent

ActionEvent 的类描述说:

And the class description for ActionEvent says:

如果任何特定 ActionEvent 实例的 id 参数不在 ACTION_FIRST 到 的范围内，将导致未指定的行为ACTION_LAST.

An unspecified behavior will be caused if the id parameter of any particular ActionEvent instance is not in the range from ACTION_FIRST to ACTION_LAST.

我的困惑来自于 ACTION_FIRST 和 ACTION_LAST 的值:

My confusion comes in with the values of ACTION_FIRST and ACTION_LAST:

/**
 * The first number in the range of ids used for action events.
 */
public static final int ACTION_FIRST                = 1001;

/**
 * The last number in the range of ids used for action events.
 */
public static final int ACTION_LAST                 = 1001;

如果 id 必须始终是 1001 以免发生未指定的行为，那为什么还要要求它?

If id must always be 1001 lest unspecified behavior occur, then why even require it?

推荐答案

ActionEvent 是 AWTEvent 的子类，它是 id 的所有者.ActionEvent 的构造函数只是将 id 传递给 super 的构造函数，然后 super (...) 检查它是否是以下之一:

ActionEvent is a subclass of AWTEvent, who is the owner of the id. The constructor for ActionEvent simply passes the id to super's constructor, where super (...) then checks that it's one of:

• ActionEvent.ACTION_PERFORMED
• ItemEvent.ITEM_STATE_CHANGED
• AdjustmentEvent.ADJUSTMENT_VALUE_CHANGED
• TextEvent.TEXT_VALUE_CHANGED

因此，ActionEvent 想要确保 super 只从他那里获得一个 ActionEvent.ACTION_PERFORMED，其中 ACTION_PERFORMED 是一个设置为 ACTION_FIRST 的常量.

So, ActionEvent wants to ensure that super only gets an ActionEvent.ACTION_PERFORMED from him, where ACTION_PERFORMED is a constant set to ACTION_FIRST).

这篇关于为什么 ActionEvent 要求提供 id?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！