我对引用它之外的类的引用函数感到有点困惑。我一直认为如果一个函数是一个公共函数，我可以继续从另一个类运行它。例如......
我正在尝试在新游戏中运行音频滑块。当我开始游戏时，音乐会很好。不幸的是，我的gameScreen类是文档类的子类。这意味着在我开始游戏之前，我的音频剪辑目前尚未添加到舞台上。我希望用户能够在玩游戏之前关闭声音（是的，即使它尚未播放，我认为这是一个很好的练习）。这意味着，如果他们直接进入选项屏幕，我需要我的音频滑块就在那里！现在，如果我开始玩，它只会添加到舞台上。
我解决这个问题的计划是进入我的选项屏幕类，然后如果运行选项屏幕功能，它会将音频剪辑添加到舞台上。这意味着我必须运行eventlistener。在这个eventlistener中，我想从我的Volume()类中引用一个函数....基本上是addToStage。我已经在我的Volume()课程中已经有了这个，我认为养成将功能从一个类复制到另一个类的习惯可能是浪费时间。所以我想，嘿，让我们去做那个功能，因为它是一个公共功能！
原来我收到错误“undefined property addToStage。”
那么我该怎样做才能使我不必将此功能直接重新复制到我的optionScreen类中？谢谢，我将在下面提供一些代码
package {
import flash.display.Sprite;
import flash.display.Graphics;
import flash.events.MouseEvent;
import flash.events.Event;
import flash.net.URLRequest;
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.media.SoundTransform;
import flash.geom.Rectangle;
public class Volume extends Sprite {
public var snd:Sound = new Sound();
public var channel:SoundChannel = new SoundChannel();
//URLRequest=new URLRequest("solitude.wav");
//Make sure you pass URLRequest an audio file on your computer.
public var req:BackgroundMusic = new BackgroundMusic();
public var boundary:Rectangle;
public var sprite:Sprite;
public var slider:Sprite;
public var xPos:Number;
public var yPos:Number;
public var vol:Number;
/*
Our request is loaded into the sound object and plays through
our channel. Volume is initially set at 50% and passed as a
transformation to our our channels soundTransform property
(a fancy way of saying volume). The init() function is called.
*/
public function Volume() {
channel=req.play();
channel.addEventListener( Event.SOUND_COMPLETE, onBackgroundMusicFinished,false,0,true );
vol=.5;
channel.soundTransform=new SoundTransform(vol);
}
/*
The init function creates and draws a rectangle and circle
to the stage and centers them based on the height and
width of the stage. In addition, a rectangle object is
created to 'contain' the sliding circle, like an imaginary box.
We pass -100 as the x value because it is added relative
to our sprite. If we set its x value at 0, or the sprites default x
value,the boundary would stop and start at the slider sprite. Change
-100 to 0 in the rectangle object to get a better idea of its use.
*/
public function onStage(e:Event):void
{
//We remove it immediately so that it doesn't get called multiple times
//As the instance is added to the display list tree
this.removeEventListener(Event.ADDED_TO_STAGE, onStage);
xPos = stage.stageWidth/2;
yPos = stage.stageHeight/2;
/* Now that we have a reference to the stage, let's go ahead and create our slider */
init();
}
public function init():void {
sprite = new Sprite();
sprite.graphics.beginFill(0x999999);
sprite.graphics.drawRect(xPos,yPos,200,5);
sprite.graphics.endFill();
addChild(sprite);
sprite.x-=sprite.width/2;
slider = new Sprite();
slider.graphics.beginFill(0xFF0000);
slider.graphics.drawCircle(xPos,yPos, 20);
slider.graphics.endFill();
addChild(slider);
slider.addEventListener(MouseEvent.MOUSE_DOWN, dragSlider);
stage.addEventListener(MouseEvent.MOUSE_UP, stopSlider);
boundary=new Rectangle(-100,0,200,0);
}
/*
dragSlider runs when the use holds the mouse button down. A
startDrag method is used on our sprite where we specify boundary
as our dragging limits. A new event handler designed
to change the mouse volume is subsequenlty called per frame, where
the slider.x property determines volume.
*/
public function dragSlider(event:MouseEvent):void {
slider.startDrag(false,boundary);
slider.removeEventListener(MouseEvent.CLICK, dragSlider);
slider.addEventListener(Event.ENTER_FRAME, changeVolume);
}
/*
Stops dragging and removes the event listener to save on space. Again,
volume will be based on the sliders current x position, which is
constantly being recalculated per frame because we used an
ENTER_FRAME event.
*/
public function stopSlider(event:MouseEvent):void {
slider.stopDrag();
slider.removeEventListener(MouseEvent.MOUSE_UP, stopSlider);
}
/*
This function is constantly recalculating the vol variable
based on the sliders x position, relative to the length of
our rectangle. Creates a decimal range from 0 to 1, where 1
represents 100% volume and 0 represents mute. Anything exceeding
100% causes distortion.
*/
public function changeVolume(event:Event):void {
vol=.5+Math.round(slider.x)/200;
channel.soundTransform=new SoundTransform(vol);
}
public function onBackgroundMusicFinished(event:Event):void
{
channel = req.play();
channel.addEventListener( Event.SOUND_COMPLETE, onBackgroundMusicFinished );
}
}
}
OptionScreen类
package {
import flash.display.MovieClip;
import flash.display.SimpleButton;
import flash.events.MouseEvent;
import flash.text.TextField;
import flash.ui.Mouse;
import flash.net.SharedObject;
public class OptionScreen extends MovieClip {
public var mainMenuButton:SimpleButton;
private var new_Volume:Volume;
public function OptionScreen() {
Mouse.show();
new_Volume = new Volume();
new_Volume.onStage();
mainMenuButtonOptions.addEventListener(MouseEvent.CLICK, onClickMainMenu,false,0,true);
}
public function onClickMainMenu(mouseEvent:MouseEvent):void
{
dispatchEvent( new NavigationEvent(NavigationEvent.MAINMENU));
}
}
}
答案 0 :(得分：2)
公共函数只能在已经在内存中实例化的实例上访问。
例如：
var redBall:Ball = new Ball();
redBall.bounce();
这是有效的，因为我在内存中有一个Ball的实例，以及包含在其中的方法的有效路径。如果我省略了实例，它会抛出一个错误。
如果要在不实例化该类的情况下调用类上的方法，则需要静态方法。
package {
public class Ball {
public static bounce():String {
return "boing!"
}
}
}
既然方法是静态的，我可以直接在类上调用方法，而不是该类的实例。
Ball.bounce() // traces "boing!"