bxml详解教程.docx

bxml详解教程.docx

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bxml详解教程

BXMLisanXML-basedmarkuplanguageforsimplifyingtheconstructionofJavaobjecthierarchies.WhileitismostoftenusedtodefinetheuserinterfaceofanApachePivotapplication,itisnotlimitedtouserinterfaceconstruction,andcanactuallybeusedtocreatehierarchiesofanyobjecttype.

ThisdocumentintroducestheBXMLlanguageandexplainshowitcanbeusedtocreateandconfigureacollectionofJavaobjects.

BXMLSerializer

Theorg.apache.pivot.beans.BXMLSerializerclassisusedtoloadastructuredefinedinaBXMLfile.Thisclassimplementstheorg.apache.pivot.serialization.Serializerinterface,whichdefinesthereadObject（）methodforreadinganobjectvaluefromaninputstream:

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publicinterfaceSerializer{

    publicTreadObject（InputStreaminputStream）

        throwsIOException,SerializationException;

    publicvoidwriteObject（Tobject,OutputStreamoutputStream）

        throwsIOException,SerializationException;

    publicStringgetMIMEType（Tobject）;

}

Forexample,thefollowingcodesnippetloadsaWindowobjectdeclaredinafilenamed"my_window.bxml":

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BXMLSerializerbxmlSerializer=newBXMLSerializer（）;

Windowwindow=（Window）bxmlSerializer.readObject（getClass（）.getResource（"my_window.bxml"））;

BXMLSerializerdoesnotimplementwriteObject（）,butdoesprovidesomeadditionalconveniecemethodsforreadingBXMLaswellasforlocalizingthedeserializedstructureusingresourcebundles.

Namespaces

InBXML,anXMLnamespacerepresentsaJavapackage.Declaringanamespaceassociatesthenamespaceprefixwiththepackage,similartohowtheimportkeywordisusedinJava.

Forexample,thefollowingsimpleBXMLassociatesthepackage"com.foo"withthe"foo"namespaceprefix:

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Barxmlns:

foo="com.foo"/>

IfthisfileweredeserializedusingBXMLSerializer,aninstanceofcom.foo.BarwouldbereturnedbythecalltoreadObject（）.ThefollowingBXML,whichmapsthecom.foopackagetothedefaultnamespace,wouldproducethesameresultswithslightlylessverbosemarkup:

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;

Morecomplexexamplesmayuseclassesdefinedinmultiplepackages;multiplenamespaceprefixescanbeusedforthispurpose.

The"bxml"Namespace

The"bxml"namespaceprefixisreservedanddefinesanumberofelementsandattributesthatareusedforinternalprocessing.ItisgenerallydeclaredontherootelementofaBXMLdocument:

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bxml="http:

//pivot.apache.org/bxml"

    xmlns="com.foo">

    ...

The"bxml"namespaceincludesthefollowing:

∙Thebxml:

idattribute,whichisusedtoassignavariablenametoanelementdeclaredinaBXMLfile.Forexample,thefollowingmarkupwouldassociateaninstanceoftheFooclasswiththeID"myFoo".Thisvariableisaddedtothedocument'svariablenamespace（whichisdifferentfromtheXMLnamespaceusedtoimportJavapackages）,andcanthenbereferencedelsewhereinthefileorbycodethatdeserializesthefile,viatheBXMLSerializer#getNamespace（）method:

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id="myFoo"/>

∙The

include>tag,whichisusedtoincludeexternalresources,includingnestedBXMLdocuments.Forexample,thefollowingmarkupwouldembedthecontentsofthe"my_include.bxml"fileinthecurrentdocument:

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includesrc="my_include.bxml"/>;

BXMLincludesareoftenusedforpartitioningcontentintomanageablepieces（forexample,whenworkingonlargeapplicationsorwithmultipledevelopers,orwhendefiningreusablecontenttemplates）.Bydefault,eachincludeisassigneditsownvariablenamespacetoavoidnamingcollisionswithancestordocuments;however,thisbehaviorcanbeoverriddenbyaddingan"inline"attributewithavalueof"true"tothe

include>tag.

∙The

script>tag,whichdefinesablockofscriptcodewithinaBXMLfile.Forexample,thefollowingscriptblockdefinesafunctionnamedfoo（）,whichcanthenbecalledfromotherscriptblocksinthedocument:

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script>

functionfoo（）{

    ....

}

script>

ThedefaultscriptinglanguageisJavaScript,butanyJVM-compatiblescriptinglanguagecanbeused.Thelanguageprocessinginstructionisusedtospecifyadifferentlanguage;forexample,Groovy:

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languagegroovy?

>

Scriptblockscanalsobedefinedineventhandlerattributesandelements.Scriptingandeventhandlingarediscussedinmoredetailbelow.

∙The

define>tag,whichisusedtodeclareobjectsthatwillexistoutsideofthehierarchybutmaybereferredtoelsewhere.

Forexample,thefollowingdefineblockdeclaresaninstanceofFoonamed"myFoo"thatisnotprocessedaspartofthedocumentflow（inotherwords,wouldnotbeaddedtoitsparentelement,ifithadone）butcanbereferredtobyvariablenamelaterinthedocument:

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define>

id="myFoo"/>

define>

∙The

reference>tag,usedtodereferenceapagevariable.Forexample,theFooinstanceinthepreviousexamplecouldbedereferencedasfollowselsewhereinthedocument:

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referenceid="myFoo"/>

Whereverthistagappears,itwilleffectivelybereplacedbythevalueofthe"myFoo"variable.

Thevariabledeferenceoperator（"$"）canalsobeusedtodereferencepagevariables.Thisisdiscussedinmoredetailbelow.

Elements

InBXML,anXMLelementthatdoesnotbeginwiththereserved"bxml"namespaceprefixrepresentsoneofthefollowing:

∙Aclassinstance

∙Apropertyofaclassinstance

∙A"static"property

Eachoftheseisdiscussedinmoredetailbelow.

ClassInstances

Ifanelement'stagnamebeginswithanuppercaseletter（anditisnota"static"propertysetter;seebelow）,itisconsideredaclassinstance.WhenBXMLSerializerencounterssuchanelement,itcreatesaninstanceofthatclass.Asdiscussedabove,theXMLnamespaceprefixisusedtodeterminetheJavapackagetowhichtheclassbelongs.

Forexample,thefollowingBXMLwouldproduceaninstanceoftheorg.apache.pivot.wtk.Labelclasspopulatedwiththetext"Hello,World!

":

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"xmlns="org.apache.pivot.wtk"/>

ClassinstanceelementsinaBXMLfilewilloftenrepresentinstancesofJavabeantypes.Internally,BXMLSerializerusesaninstanceoforg.apache.pivot.beans.BeanAdaptertowraptheinstantiatedclassandinvokeitssettermethods.Thisclassimplementstheorg.apache.pivot.collections.Dictionaryinterfaceandallowsacallertogetandsetbeanpropertyvaluesaskey/valuepairs.

However,iftheelementrepresentsatypethatalreadyimplementstheDictionaryinterface（suchasorg.apache.pivot.collections.HashMap）,itisnotwrappedanditsdictionarymethodsareuseddirectly.Forexample,thefollowingBXMLcreatesaninstanceoforg.apache.pivot.collections.HashMapandsetsits"foo"and"bar"valuesto"123"and"456",respectively:

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Howthe"foo"and"bar"attributesarehandledisdiscussedinmoredetailbelow.

InstanceProperties

Elementswhosetagnamesbeginwithalowercaseletterrepresentinstanceproperties.Aninstancepropertyelementmayrepresentoneofthefollowing:

∙Apropertysetter

∙Aread-onlysequence

∙Aread-onlydictionary

∙Aneventlistenerlist

PropertySetters

Iftheelementrepresentsapropertysetter,thecontentsoftheelement（whichmustbeeitheratextnodeoranestedclassinstanceelement）arepassedasthevaluetothesetterfortheproperty.Forexample,thefollowingBXMLcreatesaninstanceoftheLabelclassandsetsthevalueofthelabel's"text"propertyto"Hello,World!

":

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    Hello,World!

Thisproducesthesameresultastheearlierexamplewhichusedanattributetosetthe"text"property:

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"xmlns="org.apache.pivot.wtk"/>

ThefollowingexamplecreatesaninstanceofListViewandsetsthevalueofits"listData"propertytoaninstanceoforg.apache.pivot.collections.ArrayListthathasbeenpopulatedwithseveralinstancesoforg.apache.pivot.wtk.content.ListItem:

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    xmlns:

collections="org.apache.pivot.collections"

    xmlns:

content="org.apache.pivot.wtk.content">

ArrayList>

ListItemtext="A"/>

ListItemtext="B"/>

ListItemtext="C"/>

ArrayList>

Read-OnlySequences

Ifthepropertyrepresentsaread-onlysequence（abeanpropertywhosegetterreturnsaninstanceoforg.apache.pivot.collections.Sequenceandhasnocorrespondingsettermethod）,thecontentsoftheelementareaddedtothesequence.Forexample,the"tabs"propertyoftheorg.apache.pivot.wtk.TabPaneclassisaread-onlysequencerepresentingthetabpane'stabcomponents.TabscanbeaddedtoaTabPaneinBXMLasfollows:

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Read-OnlyDictionaries

Apropertyelementmayalsorepresentaread-onlydictionary（abeanpropertywhosegetterreturnsaninstanceoforg.apache.pivot.collections.Dictionarybuthasnocorrespondingsettermethod）.Forexample,the"userData"propertyoftheorg.apache.pivot.wtk.Componentclassrepresentsaread-onlydictionary:

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"

    xmlns="org.apache.pivot.wtk">