Expression Definitions

Identifier:

org.blueberry.core.expressions.definitions

Since:

3.3

Description:

This extension point allows you to create reusable extensions. They can then be used in other core expression constructs.

The reference element in a core expression will evaluated the expression definition with the evaluation context that is active for the reference element.

Configuration Markup:

<!ELEMENT extension (definition*)>

<!ATTLIST extension

point CDATA #REQUIRED

id CDATA #IMPLIED

name CDATA #IMPLIED>

point - a fully qualified identifier of the target extension point
id - an optional identifier of the extension instance
name - an optional name of the extension instance

<!ATTLIST definition

id CDATA #REQUIRED>

Provides a global definition of an expression to be used with the <reference/> expression element. This helps to reuse common expressions.

id - A globally unique identifier for the expression definition.

<!ELEMENT enablement (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

A generic root element. The element can be used inside an extension point to define its enablement expression. The children of an enablement expression are combined using the and operator.

This element represent a NOT operation on the result of evaluating it's sub-element expression.

<!ELEMENT and (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an AND operation on the result of evaluating all it's sub-elements expressions.

<!ELEMENT or (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an OR operation on the result of evaluating all it's sub-element expressions.

<!ELEMENT instanceof EMPTY>

<!ATTLIST instanceof

value CDATA #REQUIRED>

This element is used to perform an instanceof check of the object in focus. The expression returns EvaluationResult.TRUE if the object's type is a sub type of the type specified by the attribute value. Otherwise EvaluationResult.FALSE is returned.

value - a fully qualified name of a class or interface.

<!ELEMENT test EMPTY>

<!ATTLIST test

property CDATA #REQUIRED

args CDATA #IMPLIED

value CDATA #IMPLIED

forcePluginActivation (true | false) >

This element is used to evaluate the property state of the object in focus. The set of testable properties can be extended using the propery tester extension point. The test expression returns EvaluationResult.NOT_LOADED if the property tester doing the actual testing isn't loaded yet and the attribute forcePluginActivation is set to false. If forcePluginActivation is set to true and the evaluation context used to evaluate this expression support plug-in activation then evaluating the property will result in activating the plug-in defining the tester.

property - the name of an object's property to test.
args - additional arguments passed to the property tester. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.
value - the expected value of the property. Can be omitted if the property is a boolean property. The test expression is supposed to return EvaluationResult.TRUE if the property matches the value and EvaluationResult.FALSE otherwise. The value attribute is converted into a Java base type using the following rules:
- the string "true" is converted into Boolean.TRUE
- the string "false" is converted into Boolean.FALSE
- if the string contains a dot then the interpreter tries to convert the value into a Float object. If this fails the string is treated as a java.lang.String
- if the string only consists of numbers then the interpreter converts the value in an Integer object.
- in all other cases the string is treated as a java.lang.String
- the conversion of the string into a Boolean, Float, or Integer can be suppressed by surrounding the string with single quotes. For example, the attribute value="'true'" is converted into the string "true"
forcePluginActivation - a flag indicating whether the plug-in contributing the property tester should be loaded if necessary. As such, this flag should be used judiciously, in order to avoid unnecessary plug-in activations. Most clients should avoid setting this flag to true. This flag is only honored if the evaluation context used to evaluate this expression allows plug-in activation. Otherwise the flag is ignored and no plug-in loading takes place.

<!ELEMENT systemTest EMPTY>

<!ATTLIST systemTest

property CDATA #REQUIRED

value CDATA #REQUIRED>

Tests a system property by calling the System.getProperty method and compares the result with the value specified through the value attribute.

property - the name of an system property to test.
value - the expected value of the property. The value is interpreted as a string value.

<!ELEMENT equals EMPTY>

<!ATTLIST equals

value CDATA #REQUIRED>

This element is used to perform an equals check of the object in focus. The expression returns EvaluationResult.TRUE if the object is equal to the value provided by the attribute value. Otherwise EvaluationResult.FALSE is returned.

value - the expected value. The value provided as a string is converted into a Java base type using the same rules as for the value attribute of the test expression.

<!ELEMENT count EMPTY>

<!ATTLIST count

value CDATA #REQUIRED>

This element is used to test the number of elements in a collection.

value - an expression to specify the number of elements in a list. Following wildcard characters can be used:

*

any number of elements

?

no elements or one element

+

one or more elements

!

no elements

integer value

the list must contain the exact number of elements

<!ELEMENT with (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

<!ATTLIST with

variable CDATA #REQUIRED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw a ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

variable - the name of the variable to be used for further inspection. It is up to the evaluator of an extension point to provide the variable in the variable pool.

<!ELEMENT resolve (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

<!ATTLIST resolve

variable CDATA #REQUIRED

args CDATA #IMPLIED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw a ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

variable - the name of the variable to be resolved. This variable is then used as the object in focus for child element evaluation. It is up to the evaluator of an extension point to provide a corresponding variable resolver (see IVariableResolver) through the evaluation context passed to the root expression element when evaluating the expression.
args - additional arguments passed to the variable resolver. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.

<!ELEMENT adapt (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

<!ATTLIST adapt

type CDATA #REQUIRED>

This element is used to adapt the object in focus to the type specified by the attribute type. The expression returns not loaded if either the adapter or the type referenced isn't loaded yet. It throws a ExpressionException during evaluation if the type name doesn't exist at all. The children of an adapt expression are combined using the and operator.

type - the type to which the object in focus is to be adapted.

<!ELEMENT iterate (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

<!ATTLIST iterate

operator (or|and)

ifEmpty (true | false) >

This element is used to iterate over a variable that is of type java.util.Collection. If the object in focus is not of type java.util.Collection then an ExpressionException will be thrown while evaluating the expression.

operator - either "and" or "or". The operator defines how the child elements will be combined. If not specified, "and" will be used.
ifEmpty - the value return from the iterate expression if the collection is empty. If not specified then true is returned when the operator equals "and" and false is return if the operator equals "or".

<!ELEMENT reference EMPTY>

<!ATTLIST reference

definitionId CDATA #REQUIRED>

This element is used to reference an expression from the org.blueberry.core.expressions.definitions extension point. The expression definition will be evaluated within the current expression element using the current evaluation context.

definitionId - The unique id of an expression from org.blueberry.core.expressions.definitions.

Examples:

You can define and the use core expressions:


&lt;extension point="org.blueberry.core.expressions.definitions"&gt;
   &lt;definition id="com.example.parts.activeProblemsView"&gt;
       &lt;with variable="activePartId"&gt;
          &lt;equals value="org.blueberry.ui.views.ProblemsView"/&gt;
       &lt;/with&gt;
   &lt;/definition&gt;
   &lt;definition id="com.example.markers.markerSelection"&gt;
       &lt;iterate&gt;
          &lt;instanceof value="org.blueberry.core.resources.IMarker"/&gt;
       &lt;/with&gt;
   &lt;/definition&gt;
&lt;/extension&gt;

Then this expression definition can be used when composing other expressions.


&lt;enabledWhen&gt;
   &lt;reference definitionId="com.example.parts.activeProblemsView"&gt;
&lt;/enabledWhen&gt;


&lt;visibleWhen&gt;
   &lt;and&gt;
      &lt;reference definitionId="com.example.parts.activeProblemsView"/&gt;
      &lt;reference definitionId="com.example.markers.markerSelection"/&gt;
   &lt;/and&gt;
&lt;/visibleWhen&gt;

Copyright (c) 2007 IBM Corporation and others.
All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse Public License v1.0 which accompanies this distribution, and is available at http://www.eclipse.org/legal/epl-v10.html