I was wondering, if you have multiple components files that uses the same child component (but with slightly modified parameters), is it possible to assign that child component an ID with a String Constant?
When I try the following in Flex SDK 3.5, it gives me a compile error:
<!-- Example -->
<mx:Button id="{ComponentIDs.ID_BUTTON_ONE}" />
Error:
"{ComponentIDs.ID_BUTTON_ONE}" is not a valid identifier.
Any guess if this is even possible to achieve? Does the syntax differ for ID fields?
Components ids in MXML are evaluated at the compile time. So you cannot use any kind of expressions there.
So this means that even for the state tag, in its shiney new spark version, neither can any form of String constants be employed in the mxml. So of course, the next train of developer thought is how to do it in ActionScript, and everything goes hunky-dory for creating states in code using Object notation, ... until you realise that the includeIn token is an mxml compiler thing and means nothing to ActionScript ... So there you are, you have to keep using String literals in your code
Related
I am trying to make a replacement VB6 class for the Scripting.Dictionary class from SCRRUN.DLL. Scripting.Dictionary has (among other things) a "Keys" method that returns an array of keys, and a read/write "Item" property that returns the item associated with a key. I am confused about this, because both of them seem to be defaults for the class. That is:
For Each X In MyDict
Is equivalent to:
For Each X In MyDict.Keys
Which to me implies that "Keys" is the default operation for the class, but:
MyDict("MyKey") = "MyValue"
MsgBox MyDict("MyKey")
Is equivalent to:
MyDict.Item("MyKey") = "MyValue"
MsgBox MyDict.Item("MyKey")
Which to me implies that "Item" is the default operation for the class.
I've never before created a VB6 class that had a default operation, so upon realizing this, I thought perhaps I could define multiple default operations as long as they all have different signatures, which they do: Keys is nullary, the Item getter takes a Variant, and the Item setter takes two Variants. But this doesn't seem to be allowed: When I use "Tools/Procedure Attributes" to set the Keys function to be the default, and then I use it to set the Item property to be the default, the IDE complains that a default has already been set.
So I think I'm misunderstanding something fundamental here. What is going on in the Scripting.Dictionary object that makes it able to act as if "Keys" is the default in some contexts, but as if "Item" is the default in others? And whatever it is, can I accomplish the same thing in VB6?
OK, answering my own question: I haven't tried this yet, but I gather that "Item" should be made the default, and that I should add an entirely new function called "NewEnum" that looks something like the following (slightly modified from an example in Francesco Balena's "Programming Microsoft Visual Basic 6.0" book):
Public Function NewEnum() As IUnknown
Set NewEnum = m_Keys.[_NewEnum]
End Function
(where "m_Keys" is a Collection containing the keys), and then use Tools/Procedure Attributes to hide NewEnum and to set its ProcID to -4.
What you are observing is the difference between the default member and a collection enumerator. A COM object (including VB6 classes) can have both.
You can identify the default property of a class by looking in the Object Browser for the tiny blue globe or the words "default member of" in the description (see Contents of the Object Browser). The Object Browser will not identify an enumerator method, but if you look at the class's interface definition using OLE View or TypeLib Browser (free but registration required) it's DispId will be 0xfffffffc or -4.
In your own class, you can mark the default property by setting the Procedure ID to "(default)" in the Procedure Attributes dialog (see Making a Property or Method the Default). You already listed the steps for setting up the collection enumerator in your own answer, but you can find this listed as well in the Programmer's Guide topic Creating Your Own Collection Class: The House of Bricks.
Scripting.Dictionary has a dirty secret:
It does not handle enumeration at all, it returns big ugly Variant arrays and your For Each loops iterate over those.
This is one of the reasons why a Dictionary can actually be far less efficient than a standard VB6 Collection.
Does anybody know if it is possible in a compound template to use a string item in the package and execute it as if were a dreamweaver template? And whether you apply the same method to other mediators (like razor)?
Thanks
Mark
I suspect this is not possible.
Package.EvaluateExpression may be useful, but as the name suggests it'll only work on expressions, not large snippets of code with embedded expressions (i.e. TEL)
Engine.GetMediator expects a Template and returns the appropriate Mediator for it. Your problem then is that the IMediator interface only defines the Transform method, which requires an Engine, a Template and a Package.
I can't think of any elegant ways around these. Maybe write your own Mediator, but that would still expect a Package, not a string, so you'd have to first store the string based Item from another TBB.
My advice: Sounds like you need to go back to the drawing board and find an alternative solution to your problem.
I'm afraid that won't be possible on just any item in the Package, since the Engine expects Templates to be based on Tridion items.
If your Template Item is based on a Tridion Item you can probably get pretty far by starting at the Engine.GetMediator method. If it isn't, you'll have to find some way to turn it into a valid Template object.
Template template = ...
IMediator mediator = engine.GetMediator(template);
mediator.Transform(engine, template, package);
When I have to create a Component object from a Tridion-based Item in the Package, I normally do something like this:
Component component = new Component(item.GetAsXmlDocument().DocumentElement,
engine.GetSession);
I haven't tried, but expect that you can do the same for a Template - given that you start with a valid Item from the Package representing a Template to begin with. You can probably clone the XML from an existing Item or find some other way to fake it.
If you get this to work, it will work across all registered template types. The Engine provides no special treatment for the types that come with Tridion.
Why are there two different HTTPService classes in Flex?
this
and
this
And the second one inherits the first one.
Why couldn't there be a single class combining the two?
One of the objects (the first link you posted) is the HTTPService Object itself.
The second is the object that wraps the HTTPService object and gives it the additional functionality for the <mxml /> tag.
The two probably weren't combined because you don't necessarily need the implementation of the IMXMLObject and IMXMLSupport interfaces every time you need an HTTService object.
mx.rpc.http.mxml.HTTPService can also handle concurrency while the other can't.
Edit:
Although in the online documentation I see concurrency as a property of both, several sources say thats not true(and my tests didn't work when I first tried using it). Also the concurrency package is only imported into the mxml.HTTPService, not the base rpc class.
Bug Comment
Mederator comment on the docs page
There appear to be more error handling features in the URLLoader class. Using MXML to create your HTTPService is not a big difference though.
// ActionScript Style
private function myService():void {
var service:HTTPService = new HTTPService();
...service.parameters = value;...
service.send();
}
or
< !-- MXML Style -- >
< mx:HTTPService >
...< parameters >...
< /mx:HTTPService >
The first is a member of the mx.rpc.http package and is used in ActionScript code. The other version of the HTTPService class is a sublass of the first and is a member of the mx.rpc.http.mxml package. This is the version you use when you instantiate the object with the tag.
The versions are nearly identical with two significant differences: only the MXML Version implements the showBusyCursor property, which casuses an animated curser top be displayed for the duration of an HTTPService request/response cycle, and the concurrency property, which determines how multiple concurrent requests to the same network resource are handled.
The concurrency property isn't implemented in the version of the HTTPService class typically used in ActionScript because, when using ActionScript you commonly create a new HTTPService object for each new request.
Source: Adobe Flex 3 Bible - David Gassner
I'm re-writing an MXML item renderer in pure AS. A problem I can't seem to get past is how to have each item renderer react to a change on a static property on the item renderer class. In the MXML version, I have the following binding set up on the item renderer:
instanceProperty={callInstanceFunction(ItemRenderer.staticProperty)}
What would be the equivalent way of setting this up in AS (using BindingUtils, I assume)?
UPDATE:
So I thought the following wasn't working, but it appears as if Flex is suppressing errors thrown in the instanceFunction, making it appear as if the binding itself is bad.
BindingUtils.bindSetter(instanceFunction, ItemRenderer, "staticProperty");
However, when instanceFunction is called, already initialized variables on the given instance are all null, which was the cause of the errors referenced above. Any ideas why this is?
You have 2 options that I am aware of:
Option 1
You can dig into the code that the flex compiler builds based on your MXML to see how it handles binding to static properties. There is a compiler directive called -keep-generated-actionscript that will cause generated files to stick around. Sleuthing through these can give you an idea what happens. This option will involve instantiating Binding objects and StaticPropertyWatcher objects.
Option 2
There is staticEventDispatcher object that gets added at build time to classes containing static variables see this post http://thecomcor.blogspot.com/2008/07/adobe-flex-undocumented-buildin.html. According to the post, this object only gets added based on the presence of static variables and not getter functions.
Example of Option 2
Say we have a class named MyClassContainingStaticVariable with a static variable named MyStaticVariable and another variable someobject.somearrayproperty that we want to get updated whenever MyStaticVariable changes.
Class(MyClassContainingStaticVariable).staticEventDispatcher.addEventListener(
PropertyChangeEvent.PROPERTY_CHANGE,
function(event:PropertyChangeEvent):void
{
if(event.property == "MyStaticVariable")
{
someobject.somearrayproperty = event.newValue as Array;
}
});
I think you need to respond to the "PropertyChanged" event.
If you're going to do that, use a singleton instead of static. I don't think it will work on a static. (If you have to do it that way at all, there are probably a couple ways you could reapproach this that would be better).
var instance:ItemRenderer = ItemRenderer.getInstance();
BindingUtils.bindProperty(this, "myProperty", instance, "theirProperty");
After fiddling with this for a while, I have concluded that this currently isn't possible in ActionScript, not even with bindSetter. It seems there are some MXML-only features of data bindings judging by the following excerpt from the Adobe docs (though isn't it all compiled to AS code anyways)?
You cannot include functions or array
elements in property chains in a data
binding expression defined by the
bindProperty() or bindSetter() method.
For more information on property
chains, see Working with bindable
property chains.
Source: http://livedocs.adobe.com/flex/3/html/help.html?content=databinding_7.html
You can create a HostProxy class to stand in for the funciton call. Sort of like a HostFunctionProxy class which extends from proxy, and has a getProperty("functionInvokeStringWithParameters") which will invoke the function remotely from the host, and dispatch a "change" event to trigger the binding in typical [Bindable("change")] Proxy class.
You than let the HostProxy class act as the host, and use the property to remotely trigger the function call. Of course, it'd be cooler to have some TypeHelperUtil to allow converting raw string values to serialized type values at runtime for method parameters (splitted by commas usually).
Example:
eg.
var standInHost:Object = new HostFunctionProxy(someModelClassWithMethod, "theMethodToCall(20,11)");
// With BindingUtils.....
// bind host: standInHost
// bind property: "theMethodToCall(20,11)"
Of course, you nee to create such a utlity to help support such functionality beyond the basic Flex prescription. It seems many of such (more advanced) Flex bindings are usually done at compile time, but now you have to create code to do this at runtime in a completely cross-platform Actionscript manner without relying on the Flex framework.
MXML lets you do some really quite powerful data binding such as:
<mx:Button id="myBtn" label="Buy an {itemName}" visible="{itemName!=null}"/>
I've found that the BindingUtils class can bind values to simple properties, but neither of the bindings above do this. Is it possible to do the same in AS3 code, or is Flex silently generating many lines of code from my MXML?
Can anyone duplicate the above in pure AS3, starting from:
var myBtn:Button = new Button();
myBtn.id="myBtn";
???
The way to do it is to use bindSetter. That is also how it is done behind the scenes when the MXML in your example is transformed to ActionScript before being compiled.
// assuming the itemName property is defined on this:
BindingUtils.bindSetter(itemNameChanged, this, ["itemName"]);
// ...
private function itemNameChanged( newValue : String ) : void {
myBtn.label = newValue;
myBtn.visible = newValue != null;
}
...except that the code generated by the MXML to ActionScript conversion is longer as it has to be more general. In this example it would likely have generated two functions, one for each binding expression.
You can also view the auto-generated code that flex makes when it compiles your mxml file, by adding a -keep argument to your compiler settings. You can find your settings by selecting your projects properties and looking at the "Flex Compiler" option, then under "Additional compiler arguments:" add "-keep" to what is already there.
Once done Flex will create a "generated" directory in your source folder and inside you'll find all teh temporary as files that were used during compilation.
I believe flex generates a small anonymous function to deal with this.
You could do similar using a ChangeWatcher. You could probably even make a new anonymous function in the changewatcher call.