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Posted to dev@tapestry.apache.org by ta...@jakarta.apache.org on 2004/11/18 04:02:34 UTC
[Jakarta Tapestry Wiki] New: MoreFrequentlyAskedQuestions
Date: 2004-11-17T19:02:34
Editor: JohnStudarus <jo...@jhlconsulting.com>
Wiki: Jakarta Tapestry Wiki
Page: MoreFrequentlyAskedQuestions
URL: http://wiki.apache.org/jakarta-tapestry/MoreFrequentlyAskedQuestions
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New Page:
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<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><!--[if supportFields]><span
style='mso-element:field-begin'></span><span style="mso-spacerun:
yes"> </span>TOC \o "1-3" \n \h \z <span style='mso-element:field-separator'></span><![endif]--><span
class=MsoHyperlink><a href="#_Toc88480225">Where is the (some random HTML)
component? (i.e. TD)</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480226">Why isnt Initialize setting my
variables when the page is created?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480227">Where do I initialize values for a
page?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480228">How do I use the pageRenderListener
to setup my page before it is used?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480229">How do I pass information from page
to page?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480230">I just created a new page and now I
get a 'class instantiation problem'.<span style="mso-spacerun: yes">
</span>Why cant it instantiate my class?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480231">How can I share data across two
Tapestry applications?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480232">What is Spindle?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480233">What are the jwcid=$content$ tags
that Spindle places into my HTML files?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480234">When would I use the $remove$ tag?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480235">Why is my Visit object always null
or throws NoClassDefFound?</a></span><o:p></o:p></p>
<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
class=MsoHyperlink><a href="#_Toc88480236">How do I make a property in a
Component persistent?</a></span><o:p></o:p></p>
<p class=MsoNormal><!--[if supportFields]><span style='mso-element:field-end'></span><![endif]--><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480213"></a><a name="_Toc88480225"><span style='mso-bookmark:
_Toc88480213'>Where is the (some random HTML) component? (i.e. TD)</span></a></h3>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Any component that does not have a direct Tapestry component
can be represented with the Tapestry ANY component.<span style="mso-spacerun:
yes"> </span>For example, say you want to have Tapestry generate the
background color for your table using a TD component you could use <td
jwcid=@Any bgcolor=ognl:backgroundColor></td>.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480214"></a><a name="_Toc88480226"><span style='mso-bookmark:
_Toc88480214'>Why isnt Initialize setting my variables when the page is
created?</span></a> </h3>
<p class=MsoNormal>Dont worry; you arent the first person to make this
mistake.<span style="mso-spacerun: yes"> </span>Initialize isnt called when a
page is created it is called when a page is returned to the pool to be
reused.<span style="mso-spacerun: yes"> </span>Initialize is not to be used to
setup a page but instead return it to a pristine state so it can be recycled in
the pool of available pages.<span style="mso-spacerun: yes"> </span>See the
pageRenderListener interface if you want to setup state before a page is used.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480215"></a><a name="_Toc88480227"><span style='mso-bookmark:
_Toc88480215'>Where do I initialize values for a page?</span></a></h3>
<p class=MsoNormal>Youll probably want to use the pageRenderListener class to
perform any work you need when the page is accessed.<span style="mso-spacerun:
yes"> </span>Alternatively you can do some lazy initialization where objects
are created the first time they are used.<span style="mso-spacerun: yes">
</span>This isnt as clean as using Tapestry properties but it should
work.<span style="mso-spacerun: yes"> </span>For example:</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>AppointmentPage:</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Protected Date date = null;</p>
<p class=MsoNormal>Public Date getEvent() {</p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span>if ( null == date )
{</p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span>date = new
Date();</p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span>}</p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span>return date;</p>
<p class=MsoNormal>}</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480216"></a><a name="_Toc88480228"><span style='mso-bookmark:
_Toc88480216'>How do I use the pageRenderListener to setup my page before it is
used?</span></a></h3>
<p class=MsoNormal>Simply implement the PageRenderListener interface and
override the pageBeginRender() routine.<span style="mso-spacerun: yes">
</span>Often times you can just call initialize() from pageBeginRender() to
setup the page your logic in both routines may be the same.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>public abstract class AppointmentPage extends BasePage
implements PageRenderListener {</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>private Date date;</p>
<p class=MsoNormal>// this is called by Tapestry when the page is called up</p>
<p class=MsoNormal>public void pageBeginRender(PageEvent event) {</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>// do all
your pre page processing here</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>date = new
Date();</p>
<p class=MsoNormal>}</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>// this is called by Tapestry before it is return to the
pool for reuse</p>
<p class=MsoNormal>public void initialize() {</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>date = new
Date();</p>
<p class=MsoNormal>}</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480217"></a><a name="_Toc88480229"><span style='mso-bookmark:
_Toc88480217'>How do I pass information from page to page?</span></a></h3>
<p class=MsoNormal>You can use a Visit object to keep state from page to page
but this is probably overkill and cumbersome if you just want to pass some
information from one page to the next.<span style="mso-spacerun: yes">
</span>Instead you will want to create an instance of the next page, pass the
parameter and then call (activate) the next page.<span style="mso-spacerun:
yes"> </span>Here is some sample code:</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Calling Page Java:</p>
<p class=MsoNormal>public void submitAction(IRequestCycle cycle) {</p>
<p class=MsoNormal> // The next page we want to go to is the Result page</p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span>AppointmentPage
next_page = (AppointmentPage)cycle.getPage("Appointment");<br>
next_page.setDate(new Date());</p>
<p class=MsoNormal><span style="mso-spacerun: yes">
</span>next_page.setEvent(Birthday Party);</p>
<p class=MsoNormal><span style="mso-spacerun: yes">
</span>cycle.activate(next_page);</p>
<p class=MsoNormal>}</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Appointment Page:</p>
<p class=MsoNormal><property-specification name="date"
type="java.lang.Date" persistent="yes"/></p>
<p class=MsoNormal><property-specification name="event"
type="java.lang.String" persistent="yes"/></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Appointment Page Java:</p>
<p class=MsoNormal>public void setDate(Date date);</p>
<p class=MsoNormal>public void setEvent(String event); </p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480218"></a><a name="_Toc88480230"><span style='mso-bookmark:
_Toc88480218'>I just created a new page and now I get a 'class instantiation
problem'.<span style="mso-spacerun: yes"> </span>Why cant it instantiate my
class?</span></a></h3>
<p class=MsoNormal>Most likely you created your class abstract when it didnt
need to be.<span style="mso-spacerun: yes"> </span>Tapestry doesnt create an
enhanced subclass if there are no <span style='font-size:11.0pt;font-family:
Arial;color:black'><property-specification> elements.<span
style="mso-spacerun: yes"> </span>A concrete class is never created by
Tapestry in this case and since abstract classes cannot be instantiated, this
exception pops up.<span style="mso-spacerun: yes"> </span>You either need to
create a <property-specification> element or make your class concrete by
removing the abstract identifier.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:Arial;color:black'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<h3><a name="_Toc88480219"></a><a name="_Toc88480231"><span style='mso-bookmark:
_Toc88480219'>How can I share data across two Tapestry applications?</span></a></h3>
<p class=MsoNormal>Even if youre running two Tapestry applications within the
same Application Server (i.e. Tomcat) you cant share data between them within
the Application Server.<span style="mso-spacerun: yes"> </span>You can merge
the two applications together into one application and then share data through
singleton objects within the Application Server.<span style="mso-spacerun:
yes"> </span>Alternatively the two applications can share data at a lower
level common level, i.e. the operating system (message passing) or a database.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480220"></a><a name="_Toc88480232"><span style='mso-bookmark:
_Toc88480220'>What is Spindle?</span></a></h3>
<p class=MsoNormal>Spindle is a plugin for the Eclipse IDE.<span
style="mso-spacerun: yes"> </span>Eclipse is available at <a
href="http://www.eclipse.org/">www.eclipse.org</a> and Spindle is available at
spindle.sourceforge.net.<span style="mso-spacerun: yes"> </span>The Spindle
adds intelligence about Tapestry into Eclipse.<span style="mso-spacerun: yes">
</span>The end result is an IDE that is aware of Tapestry Components and Pages
by providing Wizard interfaces and navigation widgets for the creation and
viewing of Tapestry Components and Pages.<span style="mso-spacerun: yes">
</span>It is well worth a look if you intend on developing with Tapestry.<span
style="mso-spacerun: yes"> </span>Download Eclipse first and then install
Spindle through the auto update feature of Eclipse.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480221"></a><a name="_Toc88480233"><span style='mso-bookmark:
_Toc88480221'>What are the jwcid=$content$ tags that Spindle places into my
HTML files?</span></a></h3>
<p class=MsoNormal>Tapestry does not process any text outside of a <span
jwcid=$content$></span>.<span style="mso-spacerun: yes">
</span>This allows a developer to place documentation, header files or static
HTML (that should not be rendered by the Tapestry engine).<span
style="mso-spacerun: yes"> </span>Spindle places these tags into the HTML out
of convenience.<span style="mso-spacerun: yes"> </span>The can be deleted
without any problems.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480222"></a><a name="_Toc88480234"><span style='mso-bookmark:
_Toc88480222'>When would I use the $remove$ tag?</span></a></h3>
<p class=MsoNormal>The $remove$ tag is used as an aid to view static HTML
pages.<span style="mso-spacerun: yes"> </span>The Tapestry Engine removes the
tag and any text insert within when the page is rendered.<span
style="mso-spacerun: yes"> </span>This is useful when the text would otherwise
be generated dynamically and an HTML designer needs to mock up the pages
statically.<span style="mso-spacerun: yes"> </span>In the following example,
three lines would be displayed when the page is statically viewed while the
Tapestry Engine would render the one line dynamically when it is iterated
through the Foreach component.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><table></p>
<p class=MsoNormal><tr jwcid=employeeForeach></p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span><td><span
jwcid=employeeName>Jane</span></td></p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span><span
jwcid=$remove$></p>
<p class=MsoNormal><span style="mso-spacerun: yes">
</span><td>Sally</td></p>
<p class=MsoNormal><span style="mso-spacerun: yes">
</span><td>Sue</td></p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span><span/></p>
<p class=MsoNormal></tr></p>
<p class=MsoNormal></table></p>
<p class=MsoNormal><span style="mso-spacerun: yes"> </span></p>
<h3><a name="_Toc88480223"></a><a name="_Toc88480235"><span style='mso-bookmark:
_Toc88480223'>Why is my Visit object always null or throws NoClassDefFound?</span></a></h3>
<p class=MsoNormal>You might want to check that your Visit class is defined in
the application specification.<span style="mso-spacerun: yes"> </span>If it is
not defined you will run into problems when calling page.getVisit().<span
style="mso-spacerun: yes"> </span>Make sure you put a fully qualified class
name in the property.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>MyApp.application:</p>
<p class=MsoNormal><property
name="org.apache.tapestry.visit-class" value="some.example.Visit"
/></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>AppointmentPage.java:</p>
<p class=MsoNormal>Public void submit() {</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>//
getVisit() will need to be casted to the defined Visit class</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>Some.example.Visit
visit = (Some.example.Visit)getPage().getVisit();</p>
<p class=MsoNormal>}</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h3><a name="_Toc88480224"></a><a name="_Toc88480236"><span style='mso-bookmark:
_Toc88480224'>How do I make a property in a Component persistent?</span></a></h3>
<p class=MsoNormal>Pages support persistent properties so place the persistent
property in the encompassing Page and pass it into the Component.<span
style="mso-spacerun: yes"> </span>The property will remain persistent and be
passed into the Component as a parameter.<span style="mso-spacerun: yes">
</span>The Component will need not know, or care, that the property is
persistent.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
</div>
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