我是 Flash 的初学者，目前我遇到了问题。我在做一个游戏，就像太空入侵者。一开始还不错 但是，当角色击中敌人时，它提示我错误。
类型错误：
错误 #1009：无法访问空对象引用的属性或方法。在 _fla::MainTimeline/frame1126() 在 flash.display::MovieClip/gotoAndStop() 在 Enemy/eFrame()
我不知道它有什么问题。谁能帮我？
这是我的时间线的来源
stop();
//these booleans will check which keys are down
var leftDown:Boolean = false;
var upDown:Boolean = false;
var rightDown:Boolean = false;
var downDown:Boolean = false;
//how fast the character will be able to go
var mainSpeed:int = 5;
//how much time before allowed to shoot again
var cTime:int = 0;
//the time it has to reach in order to be allowed to shoot (in frames)
var cLimit:int = 12;
//whether or not the user is allowed to shoot
var shootAllow:Boolean = true;
//how much time before another enemy is made
var enemyTime:int = 0;
//how much time needed to make an enemy
//it should be more than the shooting rate
//or else killing all of the enemies would
//be impossible :O
var enemyLimit:int = 16;
//the player's score
var score:int = 0;
//this movieclip will hold all of the bullets
var bulletContainer:MovieClip = new MovieClip();
addChild(bulletContainer);
//whether or not the game is over
var gameOver:Boolean = false;
//adding a listener to mcMain that will move the character
mcMain.addEventListener(Event.ENTER_FRAME, moveChar);
function moveChar(event:Event):void{
//checking if the key booleans are true then moving
//the character based on the keys
if(leftDown){
mcMain.x -= mainSpeed;
}
if(upDown){
mcMain.y -= mainSpeed;
}
if(rightDown){
mcMain.x += mainSpeed;
}
if(downDown){
mcMain.y += mainSpeed;
}
//keeping the main character within bounds
if(mcMain.x <= 0){
mcMain.x += mainSpeed;
}
if(mcMain.y <= 0){
mcMain.y += mainSpeed;
}
if(mcMain.x >= stage.stageWidth - mcMain.width){
mcMain.x -= mainSpeed;
}
if(mcMain.y >= stage.stageHeight - mcMain.height){
mcMain.y -= mainSpeed;
}
//Incrementing the cTime
//checking if cTime has reached the limit yet
if(cTime < cLimit){
cTime ++;
} else {
//if it has, then allow the user to shoot
shootAllow = true;
//and reset cTime
cTime = 0;
}
//adding enemies to stage
if(enemyTime < enemyLimit){
//if time hasn't reached the limit, then just increment
enemyTime ++;
} else {
//defining a variable which will hold the new enemy
var newEnemy = new Enemy();
//making the enemy offstage when it is created
newEnemy.y = -1 * newEnemy.height;
//making the enemy's x coordinates random
//the "int" function will act the same as Math.floor but a bit faster
newEnemy.x = int(Math.random()*(stage.stageWidth - newEnemy.width));
//then add the enemy to stage
addChild(newEnemy);
//and reset the enemyTime
enemyTime = 0;
}
//updating the score text
txtScore.text = 'Score: '+score;
}
//this listener will listen for down keystrokes
stage.addEventListener(KeyboardEvent.KEY_DOWN, checkKeysDown);
function checkKeysDown(event:KeyboardEvent):void{
//making the booleans true based on the keycode
//WASD Keys or arrow keys
if(event.keyCode == 37 || event.keyCode == 65){
leftDown = true;
}
if(event.keyCode == 38 || event.keyCode == 87){
upDown = true;
}
if(event.keyCode == 39 || event.keyCode == 68){
rightDown = true;
}
if(event.keyCode == 40 || event.keyCode == 83){
downDown = true;
}
//checking if the space bar is pressed and shooting is allowed
if(event.keyCode == 32 && shootAllow){
//making it so the user can't shoot for a bit
shootAllow = false;
//declaring a variable to be a new Bullet
var newBullet:Bullet = new Bullet();
//changing the bullet's coordinates
newBullet.x = mcMain.x + mcMain.width/2 - newBullet.width/2;
newBullet.y = mcMain.y;
//then we add the bullet to stage
bulletContainer.addChild(newBullet);
}
}
//this listener will listen for keys being released
stage.addEventListener(KeyboardEvent.KEY_UP, checkKeysUp);
function checkKeysUp(event:KeyboardEvent):void{
//making the booleans false based on the keycode
if(event.keyCode == 37 || event.keyCode == 65){
leftDown = false;
}
if(event.keyCode == 38 || event.keyCode == 87){
upDown = false;
}
if(event.keyCode == 39 || event.keyCode == 68){
rightDown = false;
}
if(event.keyCode == 40 || event.keyCode == 83){
downDown = false;
}
}
这是来自 ENEMY 的源代码。
//This is the basic skeleton that all classes must have
package{
//we have to import certain display objects and events
import flash.display.MovieClip;
import flash.events.*;
//this just means that Enemy will act like a MovieClip
public class Enemy extends MovieClip{
//VARIABLES
//this will act as the root of the document
//so we can easily reference it within the class
private var _root:Object;
//how quickly the enemy will move
private var speed:int = 5;
//this function will run every time the Bullet is added
//to the stage
public function Enemy(){
//adding events to this class
//functions that will run only when the MC is added
addEventListener(Event.ADDED, beginClass);
//functions that will run on enter frame
addEventListener(Event.ENTER_FRAME, eFrame);
}
private function beginClass(event:Event):void{
_root = MovieClip(root);
}
private function eFrame(event:Event):void{
//moving the bullet up screen
y += speed;
//making the bullet be removed if it goes off stage
if(this.y > stage.stageHeight){
removeEventListener(Event.ENTER_FRAME, eFrame);
_root.removeChild(this);
}
//checking if it is touching any bullets
//we will have to run a for loop because there will be multiple bullets
for(var i:int = 0;i<_root.bulletContainer.numChildren;i++){
//numChildren is just the amount of movieclips within
//the bulletContainer.
//we define a variable that will be the bullet that we are currently
//hit testing.
var bulletTarget:MovieClip = _root.bulletContainer.getChildAt(i);
//now we hit test
if(hitTestObject(bulletTarget)){
//remove this from the stage if it touches a bullet
removeEventListener(Event.ENTER_FRAME, eFrame);
_root.removeChild(this);
//also remove the bullet and its listeners
_root.bulletContainer.removeChild(bulletTarget);
bulletTarget.removeListeners();
//up the score
_root.score += 5;
}
}
//hit testing with the user
if(hitTestObject(_root.mcMain)){
//losing the game
_root.gameOver = true;
_root.gotoAndStop('lose');
}
if(_root.gameOver){
removeEventListener(Event.ENTER_FRAME, eFrame);
this.parent.removeChild(this);
}
}
public function removeListeners():void{
this.removeEventListener(Event.ENTER_FRAME, eFrame);
}
}
}