I have two files,
FloorplansMaster and Floorplans.
In my FloorplansMaster I have this method inside my script tags:
public function changeView(): void
{
var floorplans:Floorplans = new Floorplans();
floorplans.changeView();
}
and I am trying to call the method changeView in the Floorplans file, which looks like this:
public function changeView():void
{
trace("Here");
}
But I keep getting this error:
Cannot access a property or method of a null object reference.
What am I doing wrong?
In Flex developers often try to access view elements before they're created.
Try calling the method in a creationComplete handler instead.
Related
I have this singleton that I'm using as a wrapper for global variables and constants, but as soon as I make some [Bindable] I get a crash on start up w/a bunch of red text in my console.
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at BrandGlobals$/get COLOUR_EVERYTHING_BACKGROUND()[C:\MyProject\src\BrandGlobals.as:14]
at BrandGlobals$cinit()
at global$init()[C:\MyProject\src\BrandGlobals.as:2]
at _mainWatcherSetupUtil/setup()
at main/initialize()[C:\MyProject\src\main.mxml:0]
at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::childAdded()[C:\autobuild\3.5.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:2131]
at mx.managers::SystemManager/initializeTopLevelWindow()[C:\autobuild\3.5.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:3400]
at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::docFrameHandler()[C:\autobuild\3.5.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:3223]
at mx.managers::SystemManager/docFrameListener()[C:\autobuild\3.5.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:3069]
BrandGlobals:
package {
public final class BrandGlobals {
[Bindable]public static var COLOUR_EVERYTHING_BACKGROUND:uint = 0xE010FF;
If I remove that [Bindable] and turn var to const there's no problem (except the obvious problem of not being able to set the variable outside of this file) but this doesn't work. Also, making the whole class [Bindable] instead of this one didn't work. When I hover my mouse over the COLOUR_EVERYTHING_BACKGROUND definition, it says "<exception thrown by getter>". 'Don't know what to think about that.
I might have guessed it was because it has no package, but I'm using another similar singleton which has [Bindable] variables and seems to work fine.
I never did get that [Bindable] twaddle.
I'm using the Flex 3.5 SDK.
I tried Brian's suggestion below, but it gave me pretty much the same error. I even tried:
{
_COLOUR_EVERYTHING_BACKGROUND = 0xE010FF;
trace("Var set."); //Breakpoint here
bLoadedFerCryinOutLoud = true;
}
[Bindable]private static var _COLOUR_EVERYTHING_BACKGROUND:uint;
private static var bLoadedFerCryinOutLoud:Boolean = false;
public static function get COLOUR_EVERYTHING_BACKGROUND():uint {
trace("Returning EVERYTHING background");
if (bLoadedFerCryinOutLoud)
return _COLOUR_EVERYTHING_BACKGROUND;
else return 0xFFFFFF;
}
What's more, if I put a breakpoint at that trace("Var set.");, Flash Builder complains that a break is not possible, because there is no executable code there.
I also noticed that in that call stack that I'm shown when this crash happens during a set and it seems to be the one that sets _COLOUR_EVERYTHING_BACKGROUND. But the only place where it is set is:
public static function SetBackground(oApp:UBIApplication):void {
_COLOUR_EVERYTHING_BACKGROUND = oApp.nBackgroundColour;
}
and breakpoints indicate that this is never called.
The documentation on using the tag has the following to say:
Using static properties as the source for data binding
You can use a static variable as the source for a data-binding expression. Flex performs the data binding once when the application starts, and again when the property changes.
You can automatically use a static constant as the source for a data-binding expression. Flex performs the data binding once when the application starts. Because the data binding occurs only once at application start up, you omit the [Bindable] metadata tag for the static constant. The following example uses a static constant as the source for a data-binding expression:
<fx:Script>
<![CDATA[
// This syntax casues a compiler error.
// [Bindable]
// public static var varString:String="A static var.";
public static const constString:String="A static const.";
]]>
</fx:Script>
<!-- This binding occurs once at application startup. -->
<s:Button label="{constString}"/>
Edit: You need to make sure that your variable is initialized before you try to read it. A static initializer is the way to go:
package {
public final class BrandGlobals {
{
_COLOUR_EVERYTHING_BACKGROUND = 0xE010FF;
trace("Var set."); //Breakpoint here
}
[Bindable]private static var _COLOUR_EVERYTHING_BACKGROUND:uint;
public static function get COLOUR_EVERYTHING_BACKGROUND():uint {
trace("Returning EVERYTHING background"); //Breakpoint here
return _COLOUR_EVERYTHING_BACKGROUND;
}
Putting in breakpoints in the places specified will let you verify that things are executing in the expected order
It turns out that the problem was assigning COLOUR_EVERYTHING_BACKGROUND to a static const elsewhere in the code, as a temporary measure. Hopefully I'll remember that assigning [Bindable]s to static consts is bad and if I don't, I'll remember the meaning of that particular cryptic reaction Flash Builder had. I'm starting to choke StackOverflow w/my questions about cryptic error messages.
Following the answer here, I have created a file called MyGlobals.as and placed some global variables and functions so that I can access it from anywhere within my project just like AS3 buil-in functions such as trace() method.
This is MyGlobals.as which is located in the src folder (top level folder)
package {
public var MessageQueue:Array = new Array();
public var main:Main;
public var BOOKING_STATUS_DATA:Object;
public function postMessage(msg:Object):void {
MessageQueue.push(msg);
}
public function processMessage():void {
var msg:Object = MessageQueue.pop();
if (msg) {
switch (msg.type) {
}
}
}
Looks like my IDE (FD4) is also recognizing all these functions and variables and also highlighting the varibles and functions just like any other built-in global functions. However, I am getting compilation errors "Accessing possibly undefined variable xxx". The code is as simple as trace(MessageQueue) inside my Main (or another classe).
I am wondering if there was any change Adboe has done recently that it can't be done now or am I missing something? I am not sure if I need to give any special instructions to FD to include this MyGlobals.as?
I am using FD4, Flex SKD 3.1, FP12.0
I am aware of the best practices which suggests to avoid using this type of method for creating global variables but I really need it for my project for my comfort which I feel best way (right now) when compared to take any other path which involves daunting task of code refactoring. I just want do something which can be done in AS3 which I guess is not a hack.
I've done some playing around; it looks like you can only define one (1) property or method at package level per .as file. It must be the same name (case-sensitive) as the .as file it is contained in.
So no, nothing has changed since the older Flash Versions.
In your case that would mean you need five separate ActionScript files along the lines of:
MessageQueue.as:
package
{
public var MessageQueue:Array;
}
main.as:
package
{
public var main:Main;
}
...etc. As you can see this is very cumbersome, another downside to the many others when using this approach. I suggest using the singleton pattern in this scenario instead.
package{
public class Singleton{
private static var _instance:Singleton=null;
private var _score:Number=0;
public function Singleton(e:SingletonEnforcer){
trace(‘new instance of singleton created’);
}
public static function getInstance():Singleton{
if(_instance==null){
_instance=new Singleton(new SingletonEnforcer());
}
return _instance;
}
public function get score():Number{
return _score;
}
public function set score(newScore:Number):void{
_score=newScore;
}
}
}
then iin your any as3 class if you import the singleton class
import Singleton
thn where u need to update the global var_score
use for example
var s:Singleton=Singleton.getInstance();
s.score=50;
trace(s.score);
same thing to display the 50 from another class
var wawa:Singleton=Singleton.getInstance();
trace(wawa.score)
I thought i should be smart and made/copy a removeAllChildren function which worked nice. But now I get "Error #2069: The Loader class does not implement this method" If i understanded it correctly so is it because I have a loaded picture in a Sprite. (But I'm almost sure it worked with the same type of pictures when I build the function as now.) I cant figure out how to go around it. Think catch error should work somehow, but havn't succeded with it. Or is something else I doing wrong?
This is the picture in R class
public static var picture:Class;
[Embed(source="picture.png")]
The child:
private var bg:Sprite=new R.picture;
canvas.addchild(bg);
My removechildrenfunction:
public static function removeAllChildren(doc:*):void {
while(doc.numChildren){
if (doc.getChildAt(0) is DisplayObjectContainer)
removeAllChildren(doc.getChildAt(0));
doc.removeChildAt(0);
}
}
you are sending removeAllChildren function parameter typed as Loader
from Loader Reference
The Loader class overrides the following methods that it inherits,
because a Loader object can only have one child display object—the
display object that it loads. Calling the following methods throws an
exception: addChild(), addChildAt(), removeChild(), removeChildAt(),
and setChildIndex(). To remove a loaded display object, you must
remove the Loader object from its parent DisplayObjectContainer child
array.
public static function removeAllChildren(doc:*):void {
if(doc is Loader && doc.parent != null)
{
doc.parent.removeChild(doc);
return;
}
while(doc.numChildren){
if (doc.getChildAt(0) is DisplayObjectContainer){
removeAllChildren(doc.getChildAt(0));
}
doc.removeChildAt(0);
}
}
I have a movieClip I am loading from the Libary and I have properly LINKED it to export with a name of myMC. This movieclip contains another movieClip and some properties. Lets call the movieClip inside: insideMC.
Here is my code:
function loadScreen()
{
var newMC:MovieClip = new myMC();
addChild(newMC);
loadButtons();
}
function loadButtons()
{
newMC.insideMC.addEventListener(MouseEvent.CLICK, homeButtons);
}
loadScreen();
HOWEVER, when I call the function loadButtons() within the loadScreen() function then I get this error.
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at iRosary_fla::MainTimeline/loadButtons()[iRosary_fla.MainTimeline::frame1:83]
at iRosary_fla::MainTimeline/loadScreen()[iRosary_fla.MainTimeline::frame1:110]
at iRosary_fla::MainTimeline/frame1()[iRosary_fla.MainTimeline::frame1:103]
It is not seeing the insideMC. Perhaps because it's calling to fast or not loaded yet. It is calling and loading the newMC tho. Just the function loadButtons() is not working because it is not seeing the insideMC movieClip. I am sure this is an easy fix but I can't find it anywhere. Thanks
newMC is a local variable in your loadScreen() method, therefore it has no scope in your loadButtons() method.
Declare newMC as a class member variable and it will have scope in loadButtons()
for example :
// in class declarations
public var newMC:MovieClip;
function loadScreen()
{
newMC = new myMC();
addChild(newMC);
loadButtons();
}
It's important to understand that :
var newMC:MovieClip = new myMC();
Creates a local variable. From your comments, it sounds like you did have newMC as a class variable. So you assumed that the above line was assigning the new instance to your class member newMC, and not the local variable you created.
Not completely sure this is your problem. But to access a movie clip within a movie clip you have to give that "insideMC" an instance name within the first movie clip. Otherwise you'll reference an object that you haven't added to the stage - a null object.
Tutorial on instance names here
through a design decission or what-so-ever Adobe changed the content of the ResultEvent fired by a HTTPService Object.
Take a look at following example:
var httpService:HTTPService = myHTTPServices.getResults();
httpService.addEventListener(ResultEvent.RESULT,resultHandler);
httpService.send();
/**
* Handels the login process
*/
function resultHandler(event:ResultEvent):void
{
// get http service
var httpService = (event.target as HTTPService);
// do something
}
It works like a charm with Flex 3.2. But when I try to compile it with Flex 3.5 or Flex 4.0 event.target as HTTPService is null.
I figured out that event.target is now an instance of HTTPOperation. That is interesting because I can't find HTTPOperation in the langref. However, I think what Flash Builder's debugger means is mx.rpc.http.Operation.
The debugger also shows that event.target has a private attribute httpService which is the instance I expected to get with event.target. But it's private, so event.target.httpService doesn't work.
If I only want to remove the EventListener I can cast event.target as EventDispatcher. But I need to use methods from HTTPService.
So: How can I get the HTTPService instance from the ResultEvent?
Any help would be appreciated. Thanks!
J.
It is useful to go through the source if you get into this. On OS X the rpc classes are here: /Applications/Adobe Flash Builder Beta 2/sdks/3.4.1/frameworks/projects/rpc/src
Inside mx.rpc.http.HTTPService there is indeed an inner-class named HTTPOperation.
It extends mx.rpc.http.AbstractOperation which in turn extends mx.rpc.AbstractOperation. Inside AbstractOperation is a getter method get service which looks to return what you need.
Since HTTPService is an inner-class it is effectively private so you'll need to cast to an AbstractOperation (either mx.rpc.http.AbstractOperation or mx.rpc.AbstractOperation).
So something like:
function resultHandler(event:ResultEvent):void
{
// get the operation
var operation:AbstractOperation = AbstractOperation(event.target);
// get http service
var httpService:HTTPService = HTTPService(operation.service);
}
edit: I take it back! Looks like Adobe is sending null for the service when it calls the super when constructing the HTTPOperation. The HTTPService is therefore only cached in the private variable httpService. I have no idea why they hide it from you but it looks like you'll have to keep your own reference around.
I solved this problem for myself.
There are some properties in HTTPService that are available from AbstractOperation. For example, I use property request which is an Object:
myService.request["service"] = myService;
And later, when I get Event which has HTTPOperation in event.currentTarget, I get my HTTPService in such way:
var eventService : HTTPService = HTTPService( AbstractOperation( event.currentTarget ).request["service"] );