我正在用 Scala 编写 GUI，并且在尝试在foreach语句中注册按钮事件时遇到了一个奇怪的问题：对于对象列表中的每个元素对象i（对象0 ...对象n )，检索到相应的 Button x = button i并使用 订阅给定的 Box box.listenTo(x)。当按下按钮时，应该执行与对象iprintln("Event triggered: " + event)相关的一些操作（在本例中为）：
import scala.swing.ComboBox
import scala.collection.mutable.Buffer
import scala.swing.Button
import scala.swing.event.ButtonClicked
import scala.swing.Action
import scala.swing.SimpleSwingApplication
import scala.swing.MainFrame
import scala.swing.GridPanel
import scala.swing.BorderPanel
object EventSet extends SimpleSwingApplication {
object PhoneKeyEvent extends Enumeration {
val Key1 = Value("1")
val Key2 = Value("2")
}
/* Constants */
private val DisplayHistory = Buffer[String]()
private val KeypadKeyEvents = List(
PhoneKeyEvent.Key1, PhoneKeyEvent.Key2)
private val PhoneKeyEventButtonNames = Map(
PhoneKeyEvent.Key1 -> "1",
PhoneKeyEvent.Key2 -> "2"
)
/* End constants */
private var PhoneKeyEventButtons = Map[PhoneKeyEvent.Value, Button]()
private def createDisplay() : ComboBox[String] = {
new ComboBox(DisplayHistory) {
// Listen to keypad keys
// Get the set of all keypad key events
val keypadEvents = List(PhoneKeyEvent.Key1, PhoneKeyEvent.Key2)
println("keypadEvents: " + keypadEvents)
keypadEvents.foreach({ event =>
println("event: " + event)
// Listen to each button representing a keypad key event
var keypadEventButton = PhoneKeyEventButtons(event)
println("keypadEventButton: " + keypadEventButton)
listenTo(keypadEventButton)
reactions += {
case ButtonClicked(keypadEventButton) => {
// TODO: fix strange bug here: adds all possible inputs
println("Event triggered: " + event)
// selection.item = selection.item + event
}
}
})
}
}
private def createPhoneControllerPanel() : BorderPanel = {
new BorderPanel() {
val keypadControlPanel = createPhoneKeyEventTypeControlPanel(KeypadKeyEvents)
add(keypadControlPanel, BorderPanel.Position.Center)
add(createDisplay(), BorderPanel.Position.North)
focusable = true
requestFocus
}
}
/**
* Creates a new {@link Button} for a given {@link PhoneKeyEvent} and adds
* the button to the global map of such buttons to their respective events;
* that means multiple buttons cannot be created for the same key event.
*/
private def createPhoneKeyEventButton(phoneKeyEvent: PhoneKeyEvent.Value) : Button = {
// Only one button can be created per key event
require(!PhoneKeyEventButtons.contains(phoneKeyEvent),
{System.err.println("A Button for the PhoneKeyEvent " + phoneKeyEvent + "has already been created.")})
val keyEventButtonName = PhoneKeyEventButtonNames(phoneKeyEvent)
val result = new Button(Action(keyEventButtonName) {
println("Key event button pressed: " + phoneKeyEvent)
})
// Add the button to the map of all created key event buttons
PhoneKeyEventButtons += phoneKeyEvent -> result
return result
}
private def createPhoneKeyEventTypeControlPanel(keyEvents : Iterable[PhoneKeyEvent.Value]) : GridPanel = {
new GridPanel(4, 3) {
// Get the intersection of all key events of the given type and the events with button names
keyEvents.foreach(phoneKeyEvent => contents += createPhoneKeyEventButton(phoneKeyEvent))
}
}
override def top = new MainFrame {
contents = createPhoneControllerPanel()
}
}
但是，我得到了一些非常奇怪的行为，单击任何 Button会触发所有此类对象操作 - 请参阅程序输出：
keypadEvents: List(1, 2)
event: 1
keypadEventButton: scala.swing wrapper scala.swing.Button$$anon$1[,0,0,0x0,invalid,alignmentX=0.0,alignmentY=0.5,border=
javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@7633f09,flags=296,maximumSize=,minimumSize=,preferredSize=,de
faultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=14,bottom=2,right=14]
,paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,te
xt=1,defaultCapable=true]
event: 2
keypadEventButton: scala.swing wrapper scala.swing.Button$$anon$1[,0,0,0x0,invalid,alignmentX=0.0,alignmentY=0.5,border=
javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@7633f09,flags=296,maximumSize=,minimumSize=,preferredSize=,de
faultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=14,bottom=2,right=14]
,paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,te
xt=2,defaultCapable=true]
Key event button pressed: 1
Event triggered: 1
Event triggered: 2
Key event button pressed: 2
Event triggered: 1
Event triggered: 2
我完全不知道为什么会这样。无论如何，我对 Scala 还是很陌生，所以这是一个非常陌生的领域，但我尝试摆弄很多东西并在 Swing 源代码中窥探，但仍然一无所知......每次迭代都使用一个循环？或者 Swing 如何一次触发每个事件？或者...？
编辑：这是两个最小化版本，它们的行为不同：
import scala.swing.SimpleSwingApplication
object ButtonEvents extends SimpleSwingApplication {
import scala.swing.Button
import scala.swing.event.ButtonClicked
import scala.swing.Action
import scala.swing.MainFrame
import scala.swing.FlowPanel
override def top = new MainFrame {
contents = new FlowPanel {
val button1 = new Button(Action("1") {
println("Button 1 pressed")
})
contents += button1
val button2 = new Button(Action("2") {
println("Button 2 pressed")
})
contents += button2
val buttons = List(button1, button2)
buttons.foreach({ button =>
listenTo(button)
reactions += {
case ButtonClicked(button) => {
println("Event triggered: " + button.text)
}
}
})
}
}
}
印刷：
Button 1 pressed
Event triggered: 1
Event triggered: 1
Button 2 pressed
Event triggered: 2
Event triggered: 2
还有一个似乎表现正确的版本（但我不确定为什么）：
import scala.swing.SimpleSwingApplication
object ButtonEvents extends SimpleSwingApplication {
import scala.swing.Button
import scala.swing.event.ButtonClicked
import scala.swing.Action
import scala.swing.MainFrame
import scala.swing.FlowPanel
override def top = new MainFrame {
contents = new FlowPanel {
val button1 = new Button(Action("1") {
println("Button 1 pressed")
})
contents += button1
val button2 = new Button(Action("2") {
println("Button 2 pressed")
})
contents += button2
val buttons = Map("1" -> button1, "2" -> button2)
buttons.foreach({ eventButton =>
listenTo(eventButton._2)
reactions += {
case ButtonClicked(eventButton._2) => {
println("Event triggered: " + eventButton._1)
}
}
})
}
}
}
打印（正确）：
Button 1 pressed
Event triggered: 1
Button 2 pressed
Event triggered: 2