ActionScript 3：“TypeError：错误＃1009：无法访问空对象引用的属性或方法。”开关

Question

我正在用ActionScript3和嵌套开关情况编写一个简单的菜单。 它所做的是使用所选菜单检查当前帧，并且如果所选菜单正在引用另一个菜单，请执行转换，然后转到选定帧，并且如果所选菜单是当前帧，则会跟踪一条简单消息。 但是，当选定的菜单和当前帧相等时，我收到了这个烦人的消息，我不知道我需要做什么来解决问题。

我的代码是：

//Import TweenMax 
import com.greensock.*;; 
import com.greensock.plugins.*; 
import flash.events.MouseEvent; 

var frameNumber:int = currentFrame; 

TweenPlugin.activate([BlurFilterPlugin]); 

//Add the buttons into an array 
var buttonsArray:Array = new Array(s1t1,s1t2,s1t3,s1t4,s1t5); 

//Loop through the buttons array 
for (var i:uint = 0; i < buttonsArray.length; i++) { 
    //Add event listeners for the button 
    buttonsArray[i].addEventListener(MouseEvent.MOUSE_OVER, mouseOverButton); 
    buttonsArray[i].addEventListener(MouseEvent.CLICK, buttonClicked); 
} 

//Move the buttonBackground under the home button (= starting position) 
buttonBackground.x = s1t1.x; 
buttonBackground.y = s1t1.y; 

//Make the buttonBackground a bit bigger than the home button 
buttonBackground.width = s1t1.width + 10; 
buttonBackground.height = s1t1.height + 10; 

//Tween the buttonBackground to a random color using TweenMax 
TweenMax.to(buttonBackground, 0.1, {tint: Math.random() * 0xffffff}); 

//This function is called when the mouse is over a button 
function mouseOverButton(e:MouseEvent):void { 
    //trace(e.target.name + " was touched!"); 
    //Assign the button to a local variable 
    var button:MovieClip = (MovieClip)(e.target); 

    //Calculate the new target width and height for the buttonBackground 
    var targetWidth:Number = button.width + 10; 
    var targetHeight:Number = button.height + 10; 

    //Tween the buttonBackground's position, size and color (color is random) 
    TweenMax.to(buttonBackground, 0.5, {x: button.x, y: button.y, 
    width:targetWidth, height:targetHeight, tint: Math.random() * 0xffffff}); 
} 

//This function is called when a button is clicked 
function buttonClicked(e:MouseEvent):void { 
    switch(e.target.name){ 
     case "s1t1": 
      switch (currentFrame){ 
       case 5: 
        trace("Nowhere to go!"); 
       break; 
       case 6: 
        var myTM:TransitionManager = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        var myTM:TransitionManager = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        var myTM:TransitionManager = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        var myTM:TransitionManager = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 5; 
      myTM.addEventListener("allTransitionsOutDone", doneTrans) 
     break; 
     case "s1t2": 
      switch (currentFrame){ 
       case 5: 
        var myTM:TransitionManager = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        trace("Nowhere to go!"); 
       break; 
       case 7: 
        var myTM:TransitionManager = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        var myTM:TransitionManager = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        var myTM:TransitionManager = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 6; 
      myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t3": 
      switch (currentFrame){ 
       case 5: 
        var myTM:TransitionManager = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        var myTM:TransitionManager = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        trace("Nowhere to go!"); 
       break; 
       case 8: 
        var myTM:TransitionManager = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        var myTM:TransitionManager = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 7; 
      myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t4": 
      switch (currentFrame){ 
       case 5: 
        var myTM:TransitionManager = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        var myTM:TransitionManager = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        trace("Nowhere to go!"); 
       break; 
       case 7: 
        var myTM:TransitionManager = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        var myTM:TransitionManager = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 8; 
      myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t5": 
      switch (currentFrame){ 
       case 5: 
        var myTM:TransitionManager = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        var myTM:TransitionManager = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        var myTM:TransitionManager = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        var myTM:TransitionManager = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        trace("Nowhere to go!"); 
       break; 
      } 
      frameNumber = 9; 
      myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
    } 
} 
function doneTrans(e:Event):void{ 
    trace("Going frame: "+frameNumber); 
    gotoAndStop(frameNumber); 
} 

我使用Flash CS5和 “使用GreenSock” 插件和我的错误是：

TypeError: Error #1009: Cannot access a property or method of a null object reference. 
     at _009_fla::MainTimeline/buttonClicked() 

Answer 1

的问题是，当你添加一个事件侦听器时myTM它不在那里（当单击当前页面的菜单按钮时），所以我通过检查myTM是否被实例化（非空）并且如果是这样添加事件监听器来快速修复，希望它修复您的问题。

替换为您buttonClicked功能这一项：

function buttonClicked(e:MouseEvent):void { 
    //declaring new variables inside conditional cases is a bad practice 
    var myTM:TransitionManager; 
    switch(e.target.name){ 
     case "s1t1": 
      switch (currentFrame){ 
       case 5: 
        trace("Nowhere to go!"); 
       break; 
       case 6: 
        myTM = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        myTM = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        myTM = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        myTM = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 5; 
      //myTM.addEventListener("allTransitionsOutDone", doneTrans) 
     break; 
     case "s1t2": 
      switch (currentFrame){ 
       case 5: 
        myTM = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        trace("Nowhere to go!"); 
       break; 
       case 7: 
        myTM = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        myTM = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        myTM = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 6; 
      //myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t3": 
      switch (currentFrame){ 
       case 5: 
        myTM = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        myTM = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        trace("Nowhere to go!"); 
       break; 
       case 8: 
        myTM = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        myTM = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 7; 
      //myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t4": 
      switch (currentFrame){ 
       case 5: 
        myTM = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        myTM = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        trace("Nowhere to go!"); 
       break; 
       case 7: 
        myTM = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        myTM = new TransitionManager(s1text5); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       default: 
        trace("Nowhere to go!"); 
      } 
      frameNumber = 8; 
      //myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
     case "s1t5": 
      switch (currentFrame){ 
       case 5: 
        myTM = new TransitionManager(s1text1); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 6: 
        myTM = new TransitionManager(s1text2); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 7: 
        myTM = new TransitionManager(s1text3); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 8: 
        myTM = new TransitionManager(s1text4); 
        myTM.startTransition({type:Fade, direction:Transition.OUT, duration:0.25, easing:Back.easeOut}); 
       break; 
       case 9: 
        trace("Nowhere to go!"); 
       break; 
      } 
      frameNumber = 9; 
      //myTM.addEventListener("allTransitionsOutDone", doneTrans); 
     break; 
    } 

    //if myTM is not null (not empty) add the event listener 
    if (myTM) 
    { 
     myTM.addEventListener("allTransitionsOutDone", doneTrans); 
    } 
} 

有一个很大的空间，在你的代码的改进，例如，它可以重做只使用一个开关或很多更好的方法，但我不”不想大量改变你的代码。