用于Copter风格的道奇游戏AS3的错误代码#1009

Question

请您看一下我的代码，告诉我为什么我会收到这个错误：

TypeError:错误#1009:无法访问空对象引用的属性或方法。at Arm/update()

我是，而不是我刚刚学到的使用文档类的，无法让这些类工作。下面是我从下面开始的教程：http://eyes-squared.co.uk/blog/making-a-copter-style-game-the-projects/

主要代码：

stop();


import flash.events.Event;
import flash.events.MouseEvent;


var mouseIsDown = false; // mouse isn't held at start
var speed = 0; // no speed at the start
var score = 0; // start with no score!

// check for collisions every frame
addEventListener(Event.ENTER_FRAME, mainLoop);
// add 2 event listeners for the mouse button
stage.addEventListener(MouseEvent.MOUSE_DOWN, clicked);
stage.addEventListener(MouseEvent.MOUSE_UP, unclicked);

// explain the mouse functions
function clicked(m:MouseEvent) {
    mouseIsDown = true;
}

function unclicked(m:MouseEvent) {
    mouseIsDown = false;
}

//// explain the main game loop
function mainLoop(e:Event) {
    // update the score!
    score = score + 10;
    // update the text field
    Output.text = "Score: "+score;
    // move the player based on the mouse button
    if (mouseIsDown) {
        // take something off the speed
        speed -= 2; // accelerate upwards
    } else {
        speed += 2;
    }
    // limit the speed
    if (speed > 10) speed = 10;
    if (speed < -10) speed = -10;
    // move the player based on the speed
    firefly.y += speed;
    // loop through everything on screen
    for (var i = 0; i<numChildren; i++) {
        // check to see if this object is a block
        if (getChildAt(i) is Block || getChildAt(i) is Boundary || getChildAt(i) is Block2 || getChildAt(i) is Arm) {
            var b = getChildAt(i) as MovieClip;
            // this means the object is a block
            // check the block against the player object
            if (b.hitTestObject(firefly)) {
                // make an explosion
                for (var counter = 0; counter<12; counter++) {
                    // make a new Boom object
                    var boom = new Boom();
                    boom.x = firefly.x;
                    boom.y = firefly.y;
                    // randomly rotate boom
                    boom.rotation = Math.random()*360;
                    // randomly scale it
                    boom.scaleX = boom.scaleY = 0.5+Math.random();
                    // add the boom to the world
                    addChild(boom);
                }
                // hide the player
                firefly.visible = false;
                removeEventListener(Event.ENTER_FRAME, mainLoop);

                if(b.hitTestObject(firefly)){
                    nextFrame();
                }
            }
        }
    }
}

Answer 1

提示是，您的错误引用了名为Arm的类/ MovieClip中的一个名为update()的函数，该函数未包含在初始帖子中。

假设类中没有任何代码，并且所有东西都在FLA中，那么查看名为Arm的对象的Flash中的Library面板，打开它，然后查看框架脚本中的update()函数。

特定的错误意味着您试图对尚未创建的对象(或其属性的属性)执行操作，或者不存在。例如，如果删除或重新标记了Arm符号中的命名对象，然后在update函数中引用该对象，则会遇到空对象错误。

如果您查看代码，并且仍然难以确定哪个对象为null，请尝试在update函数的每一行之间放置以下跟踪语句：

trace(1);
...
trace(2);
...

因为这是一个运行时错误，Flash将在每一行跟踪给定的数字，直到它碰到该错误，并删除线程。观察输出面板，看看哪些数字被跟踪，您就会知道，故障线路是直接跟踪的最高数字之后。然后，您可以考虑为什么该行上的某个内容可能为空。祝好运!