Re: [Tapestry-developer] component definitions

kyle dawkins Thu, 19 Dec 2002 10:39:08 -0800

Hey, I'm chiming in late here, but this discussion seems like we're smacking our heads against a brick wall a little bit. I think this whole confusion is kind of related to the problem that lots of developers have understanding the difference between "Class" and "Instance". Christian wants to put an *instance* of a component on lots of pages, and doesn't seem to get that he needs to (to borrow the OO term) *instantiate* it. In Java, you need to instantiate objects that you want to use, or you create static methods that do it for you. If you want a singleton for example, you still need to instantiate it once, and you need to do that work yourself. This is no different to how you set up your pages in Tapestry (or WebObjects, of course), except it's not classes we're talking about, it's components.

If you want an instance of your calendar object on a whole slew of different pages, create a component that needs no parameters and displays your component with all of its parameters set the way you like them, and then put *that* component on all your pages. You get your calendar all nicely configured and it doesn't take a bunch of lines in your .jwc files, as described by MindBridge below.

Or is that still too hard?

Kyle Dawkins
Central Park Software

On Thursday, Dec 19, 2002, at 12:27 US/Eastern, Mind Bridge wrote:

Hi Christian,

I think am clear as to what you suggest (see below for an example). Here is
an example of what I am talking about:
New Component (Tapestry 2.4):
-----------------------------
1 x defining a new component
	5 lines + 'component configuration', 1 line template, 1 line alias
N x using the new component
	1 line in template
huh? Sorry I really cannot follow. What are those 5 lines?
JWC:
----
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE component-specification PUBLIC "-//Howard Lewis Ship//Tapestry
Specification 1.3//EN"
"http://tapestry.sf.net/dtd/Tapestry_1_3.dtd";>
<component-specification class="net.sf.tapestry.BaseComponent">


<component id="compId" type="SomeComponentThatNeedsToBeConfigured">
<binding name="someParameter1" expression="some value 1"/>
<binding name="someParameter2" expression="some value 2"/>
</component>


</component-specification>

Template:
---------
<span jwcid="compId"/>

App spec:
---------
<component-alias type="ConfiguredComponent" specification-path="..."/>

Using the new component in every relevant page (same effect as what you
suggest):
----------------------------------------------------------------------- -
<span jwcid="@ConfiguredComponent"/>
What is "? lines + 'component configuration'"?
What you suggest is to put the following block in the App spec instead:


<component id="compId" type="SomeComponentThatNeedsToBeConfigured">
<binding name="someParameter1" expression="some value 1"/>
<binding name="someParameter2" expression="some value 2"/>
</component>


and make it possible for that component to be used in all application pages
and components in the following way:

<span jwcid="compId"/>

As you can see, the difference between the above approaches is precisely 7
lines in the locations that I have specified. I have put the '? lines'
because it is possible that additional code may be needed, although it is
not apparent that it is at this point.

Note that there is basically no difference between the two approaches when
'use' is concerned -- they both require one short line.

I have to go out in about -5 minutes, so just a few quick final remarks for
now:
1. make type aliases optional (tapestry 2.4?)
This is where we come from, actually. In the pre-2.2 world aliases were
optional and Spindle, for example, did not use them at all. This is not very
compatible with the notion of libraries, however. Please have a look at the
mailing list archives on this topic, or perhaps Howard can explain his point
of view.

I hope this makes things clearer.

You proposal is definitely interesting, but I think the 'composing
component' one described above is very close.

Best regards,
-mb

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Re: [Tapestry-developer] component definitions

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