I've got 2 files, my Application and a custom component.
In my component I have a httpservice and a string named _requestUrl that is bindable. The httpservice uses this.
<mx:HTTPService id="srv"
url="{_requestUrl}"
result="parseHttpResult(event)"
resultFormat="xml"
method="GET"
useProxy="false">
In my application file I make an instance of my component in the onCreationComplete function.
In this function if I say
mycomponent._urlRequest ="http://example.com" the httpservice throws a null url error but if I say mycomponent.srv.url="http://example.com" it works fine.
Why is this?
EDIT:
<mx:Script>
import mx.events.FlexEvent;
import components.custom
private var comp:custom= new custom()
private var comp:custom= new custom()
public function setVars(event:FlexEvent):void
{
comp._requestUrl = "http://example.com"
comp.setVars(event)
pform.addChild(comp)
}
//creationComplete="setVars(event)"
</mx:Script>
Because when components are initialized, your _requestUrl is null in the beginning anyway, thats why you get this error. And your url of srv is bound to null value on initialization.
Flex creates components in phases, so if you set variable in creationComplete etc, creationcomplete is called after it has completely created the components, it is called after few millseconds of the initialization of class.
So at time of initialization, by default everything is null except you initialize it inline init expression as below
// this will not be null...
var myUrl:String = "my url";
// this will be null
var myUrl2:String;
// binding above value may give null exception
// because it is null at time of initialization
Even to me first time it was confusing but in Flex's context, Initialized event is called before "CreationComplete" and in normal programming context, we think that we create and initialize object later.
In your example, binding starts working even before "creationComplete" is called that causes it to report null pointer exception, so before this event, your object's property is any way null right.
Related
I am new to Flex (got assigned to maintain an old project at work) and am having some trouble getting data binding to work correctly. I have a popup form class, AddOffer.mxml which uses a model AddOfferModel.as. On my popup form, I have the following component:
<mx:FormItem label="{getResource('addOffer.form.OFFER_DATE')}:"
labelWidth="90">
<views:OfferWindowDatesFragment
id="offerWindowField"
start="{model.offerStartDate}"
stop="{model.offerStopDate}" />
</mx:FormItem>
My AddForm.mxml file also has some embedded actionscript where I define my 'model' variable:
[Bindable]
public var model:AddOfferModel;
The model variables I am trying to bind to are standard getters/setters and look like this inside AddOfferModel.as:
[Bindable]
public function set offerStartDate(val:EditableInstant):void
{
_offerStartDate = val;
}
public function get offerStartDate():EditableInstant
{
return _offerStartDate;
}
private var _offerStartDate:EditableInstant;
[Bindable]
public function set offerStopDate(val:EditableInstant):void
{
_offerStopDate = val;
}
public function get offerStopDate():EditableInstant
{
return _offerStopDate;
}
private var _offerStopDate:EditableInstant;
Inside the OfferWindowDatesFragment component class, the start and stop variables look like this:
[Bindable]
public function set start(val:EditableInstant):void
{
_start = val;
}
public function get start():EditableInstant
{
return _start;
}
private var _start:EditableInstant;
[Bindable]
public function set stop(val:EditableInstant):void
{
_stop = val;
}
public function get stop():EditableInstant
{
return _stop;
}
private var _stop:EditableInstant;
Basically, I just want to bind the start and stop variables in my OfferWindowDatesFragment class to the offerStartDate and offerStopDate variables in the AddOfferModel.as file. Whenever I access the start/stop variables in functions inside the OfferWindowDatesFragment class, they are null.
I have an event listener function that gets triggered in OfferWindowDatesFragment anytime a user selects a new date, it looks like this:
private function changeOfferDate():void
{
start.currentValue = offerDateEditor.start;
stop.currentValue = offerDateEditor.stop;
}
Every time I reach this function, it throws up an error because 'start' and 'stop' are both null ... but should have been initialized and bound already. If I look at the variables in the debugger, I can confirm that values on the right side of the assignment expression are valid, and not what is causing the error.
I am not real familiar with how initialization works in Flex, and I assumed as long as I instantiated the component as seen in the first code snippet at the top of my post, it would initialize all the class variables, and setup the bindings. Am I missing something? Perhaps I am not properly initializing the model or class data for AddForm.mxml or AddFormModel.as, thereby binding null references to the start/stop fields in my OfferWindowDatesFragment class?
Any help would be greatly appreciated. Thanks!
EDIT:
I looked into this further and tried using Mate to inject the 'model' variable inside AddOffer.mxml with a valid AddOfferModel object:
<Injectors target="{AddOffer}" debug="{debug}">
<ObjectBuilder generator="{AddOfferModel}" constructorArguments="{scope.dispatcher}" cache="local"/>
<PropertyInjector targetKey="model" source="{lastReturn}" />
</Injectors>
I load the AddOffer.mxml dialog as the result of a button click event on another form. The function that pops it up looks like this:
public function addOffer():void
{
var addOfferDialog:AddOffer = new AddOffer();
addOfferDialog.addEventListener("addOffer", addOfferFromDialog);
modalUtil.popup(addOfferDialog);
}
It doesn't seem to be assigning anything to the 'model' variable in AddOffer.mxml. Does loading a view/dialog this way not trigger an injection from Mate by chance? (I realize this last part might belong in the Mate forums, but I'm hoping somebody here might have some insight on all of this).
In AddOffer.mxml, you have this code:
[Bindable]
public var model:AddOfferModel;
Is there something outside AddOffer.mxml that is setting this to a valid AddOfferModel? There should be. The nature of how the Flex component life cycle means that you can expect that things may be null at times as a View builds. So you should build your components to be able to "right themselves" after receiving bad data, if the data eventually comes good.
Data binding is one way to do this, but it may not paper over everything depending on what else is going on.
Have you verified that the model value you're getting is not null at the point where the user selects the date and that its offerStartDate and offerEndDate properties have been populated with valid EditableInstants? If both of those are correct, I'd start looking for pieces of the Views that expect to have stuff at a given instant and then don't recover if it is provided later.
Flex having any init(), destroy() method. Like Servlet init()method will run at Application initialize and never call it again if Refresh the Page also.
I would suggest not using initialize event, and instead use creationComplete. All UIComponent dispatch that event when they are finished constructing themselves AND their children. This event is executed once after the component has been initialized, had a chance to measure itself, perform layout, and added to the stage.
<mx:Application ... creationComplete="init()"/>
<mx:Script>
private function init() : void {
... // put your initialization routine here
}
</mx:Script>
</mx:Application>
All flex components, including the root "application" component have an "initlize" event that you can listen to and handle.
If you'd like it to only run ONCE, regardless of refresh, you'd need to store a variable somehow, such as with a local shared object. That's pretty easy to do:
private function onInit():void{
var appSO:SharedObject = SharedObject.getLocal("yourappdata");
if(appSO.size < 0){
//do your init code
appSO.data.initialized = true;
appSO.flush();
}
}
Since I found the webpages explaning the bindable propety quite confusing,so I would like to post my question here,which is quite simple,if I declare a variable to be bindable,does that mean whenever I changed the value of this variable in another class,all appearence of this variable will be synchronized to be the same value at the same time?
Say,if boolean variable "select" is declared to be bindable in Class A and default to be false,and we have an if statement in class A like if(select).
Then in another class,we changed the value of "select" to be true,will that if(select) statement pass the test ?
Also,how about the following setter method that is defined to be bindable:
[Bindable]
public function set isShowingAvg(b:Boolean):void
{
_isShowingAvg = b;
hasChanged();
}
Does this code imply that changing the value of _isShowingAvg is also going to be broadcasted?
Thanks in advance.
Thanks for your idea.
Declaring a property as Bindable means that when you change the value, an event will get broadcasted. This event enables data binding, but it's not necessarily automatic.
If the consuming class is MXML and you use brackets, like this:
<mx:Button enabled="{selected}" />
Then the MXML compiler will generate the appropriate binding code and anytime selected changes, enabled will also get changed.
If you're using it outside MXML then you'll either subscribe to the event to detect changes or use BindingUtils.
In your example I think you need to mark the getter [Bindable] and not the setter.
example:
public static const SHOWING_AVG_CHANGED:String = "showingAvgChangedEvent";
[Bindable(event="showingAvgChangedEvent")]
public function get isShowingAvg():Boolean
{
return _isShowingAvg;
}
public function set isShowingAvg(isShowing:Boolean):void
{
_isShowingAvg = isShowing;
dispatchEvent(new Event(SHOWING_AVG_CHANGED));
}
I'm not sure if I'm misunderstanding the binding in Flex. I'm using Cairngorm framework. I have the following component with code like:
[Bindable]
var _model:LalModelLocator = LalModelLocator.getInstance();
....
<s:DataGroup dataProvider="{_model.friendsSearchResults}"
includeIn="find"
itemRenderer="com.lal.renderers.SingleFriendDisplayRenderer">
<s:layout>
<s:TileLayout orientation="columns" requestedColumnCount="2" />
</s:layout> </s:DataGroup>
in the model locator:
[Bindable]
public var friendsSearchResults:ArrayCollection = new ArrayCollection();
Inside the item renderer there is a button that calls a command and inside the command results there is a line like this:
model.friendsSearchResults = friendsSearchResults;
Putting break points and stepping through the code I confirmed that this like gets called and the friendsSearchResults gets updated.
To my understanding if I update a bindable variable it should automatically re-render the s:DataGroup which has a dataProvider of that variable.
There's nothing obviously wrong in the code sample. It should work so I think there's a problem elsewhere.
I would recommend setting a breakpoint where the dataProvider is assigned and also where model.friendsSearchResults is assigned. Make sure they're both pointing to the same object instance. Then step through the property assignment and corresponding event.
To make debugging easier you can switch to using a named event instead of the default. With a named event, only event listeners interested in your particular property are triggered instead of any listeners listening for any property change. This is easier to debug and will run faster. For example, change:
[Bindable]
public var results:ArrayCollection;
to
[Bindable("resultsChanged")]
private var _results:ArrayCollection;
public function get results():ArrayCollection {
return _results;
}
public function set results(value:ArrayCollection):Void {
_results = value;
dispatchEvent(new Event("resultsChanged"));
}
Another thing to keep in mind is that bindings hide certain errors like null reference exceptions. They assume the value simply isn't available yet and suppress the error. Stepping through the assignment and related bindings will help find a problem like this.
I have a custom actionscript object defined as bindable with a number of public properties.
[Bindable]
public class MyObject extends Object {
public var mobileNumber:String;
...
In my mxml I have:
<mx:Script><![CDATA[
import mx.binding.utils.BindingUtils;
import org.test.MyObject;
[Bindable]
private var obj: MyObject = new MyObject();
]]></mx:Script>
<mx:Label text="Mobile Number" id="mobileNumberLabel"/>
<mx:TextInput id="mobileNumberText" text="{obj.mobileNumber}" />
<mx:LinkButton label="Load" id="loadButton" enabled="true" click="obj = obj.load();"/>
<mx:LinkButton label="Save" id="saveButton" enabled="true" click="obj.write();"/>
My issue is that when I enter a new value in the field for mobile number and then click the save button, the value typed is not logged out... i.e.:
public function write():void {
var bytes:ByteArray = new ByteArray();
trace("write - mobile:" + this.mobileNumber);
bytes.writeObject(this);
EncryptedLocalStore.setItem(KEY, bytes);
}
I also tried adding in:
private function init():void {
BindingUtils.bindProperty(mobileNumberText, "text", obj, "mobileNumber");
}
but no luck with that either.
I'm probably missing something simple here, but not sure what it is. Hope you can help, thanks.
tst's answer is correct - bindings are one-way. I'm guessing you already knew that though, since you tried to setup the reverse binding in your init() method.
However, there's two problems with your init() method.
First, it's not clear where you put that init() method, or what calls it.
Second, you got the method parameters backwards.
What I typically do in situations like this is either use the mxml tag as the first responder suggested, or if I'm in AS3 code, I do something like this:
private function onCreationComplete(event:Event):void
{
BindingUtils.bindProperty(obj, "mobileNumber", mobileNumberText, ["text"]);
}
Note a couple of points here:
1/ BindingUtils.bindProperty() is "left hand side = right hand side". Thus, it's kinda like writing
obj.mobileNumber = mobileNumberText.text;
Or, closer to what is "actually going on" inside the binding classes:
obj["mobileNumber"] = mobileNumberText["text"];
2/ BindingUtils.bindProperty() actually wants an array as the last param. This is so that you can do "chained properties" logically like:
obj.mobileNumber = mobileNumbersGrid.selectedItem.text;
which would be
BindingUtils.bindProperty(obj, "mobileNumber", mobileNumbersGrid,
["selectedItem", "text"]);
3/ Best practice tip: if you're binding a property chain whose initial member is a property of yourself (this), then write it as:
BindingUtils.bindProperty(obj, "mobileNumber", this,
["mobileNumbersGrid", "selectedItem", "text"]);
This neatly handles the case where your "right hand side object" this.mobileNumbersGrid instance itself is replaced with a new instance object.
4/ If you ever reassign obj ("the left hand side"), you need to create a new binding to the new obj instance. Typically, you do this by turning the local obj property into a getter/setter pair like this:
public function get obj():MyObject
{
return _obj;
}
private var _obj:MyObject = new MyObject();
public function set obj(value:MyObject):void
{
_obj = value;
BindingUtils.bindProperty(_obj, "mobileNumber", mobileNumberText, ["text"]);
}
(Note: to be really careful, you'd stash the returned value from BindingUtils.bindProperty() which is a ChangeWatcher instance, and you'd unwatch() to prevent the old object from receiving property changes)
Hope this helps. Bindings are among the most powerful tools in the Flex framework, but can cause a lot of headaches when used poorly. In particular, be aware of memory leaks and "unexpected updates" when bindings are left "hanging around".
This code:
<mx:TextInput id="mobileNumberText" text="{obj.mobileNumber}" />
makes a one-directional binding between obj.mobileNumber and mobileNumberText.text. What you need is an additional reverse binding - add the following line to your code and it will work:
<mx:Binding source="mobileNumberText.text" destination="obj.mobileNumber"/>
Did you try implementing IEventDispatcher, or extending EventDispatcher?
Bindings work through dispatching of PropertyChangeEvents, so maybe this is the problem?
also, I am not sure, whether bindings work on variables, or whether they require properties (getters/setters).
You should try compiling with -keep-generated-actionscript and see if the resulting code makes any sense, i.e. dispatches any events, if the variable is accessed ...