为MainFrame编写自己的密钥发布器

Question

我希望我的MainFrame能够捕捉关键事件。我没有找到任何已经在其中的关键出版商，所以我将编写我自己的...我有这样的东西：

class ImageView(image: ImageIcon, parent: UIElement = null) extends MainFrame {

  object keys extends Publisher {
    peer.addKeyListener(new KeyListener {
      def keyPressed(e: java.awt.event.KeyEvent) {
        publish(new KeyPressed(e))
      }

      def keyReleased(e: java.awt.event.KeyEvent) {
        publish(new KeyReleased(e))
      }

      def keyTyped(e: java.awt.event.KeyEvent) {
        publish(new KeyTyped(e))
      }
    })
  }

  listenTo(keys)

  reactions += {
     case KeyPressed(_, key,_,_) =>
       if (key == Key.Escape) dispose
  }

}

无论如何，当我按任何键时，我都会得到这样的异常：

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: scala.swing.Frame$$anon$1 cannot be cast to javax.swing.JComponent
    at scala.swing.event.KeyPressed.<init>(KeyEvent.scala:33)
    at pip.gui.ImageView$keys$$anon$2.keyPressed(ImageView.scala:35)
    at java.awt.Component.processKeyEvent(Component.java:6225)
    at java.awt.Component.processEvent(Component.java:6044)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Window.processEvent(Window.java:1836)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Window.dispatchEventImpl(Window.java:2478)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1850)
    at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:712)
    at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:990)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:855)
    at 
.
.
.
.
(continues long further)

我从Component.keys调出了这段发布器代码，那么这里到底出了什么问题呢？

提前谢谢你，托尼

Answer 1

在库中这似乎是一个糟糕的设计。纵观KeyEvent.scala，有各种各样的类型转换到JComponent，JFrame是java.awt.Component的子类，但不是JComponent，所以调用listenTo(keys)应该是不可能的。

您想要的是监听框架的contents中最顶部的组件。例如：

import scala.swing._; import event._
import javax.swing._

class ImageView(image: ImageIcon, parent: UIElement = null) extends MainFrame {
   val b = new BorderPanel {
      listenTo( keys )
      reactions += {
         case KeyPressed(_, key,_,_) =>
            println( "PRESSED : " + key )
            if (key == Key.Escape) dispose
      }
   }
   contents = b
}

val w = new ImageView( null )
w.peer.setSize( 200, 200 )
w.visible = true
w.b.requestFocus

requestFocus是必不可少的，因为即使你点击它，面板本身也不会请求焦点，否则它就不会收到按键事件。