org.eclipse.core.expressions

Interface IEvaluationContext

All Known Implementing Classes:

EvaluationContext

public interface IEvaluationContext

An evaluation context is used to manage a set of objects needed during XML expression evaluation. A context has a parent context, can manage a set of named variables and has a default variable. The default variable is used during XML expression evaluation if no explicit variable is referenced.

This interface is not intended to be implemented by clients. Clients are allowed to instantiate EvaluationContext.

Since:

3.0

Restriction:

This interface is not intended to be implemented by clients.

Restriction:

This interface is not intended to be extended by clients.

Field Summary

Fields

Modifier and Type	Field and Description
static Object	UNDEFINED_VARIABLE Represents the value used by variables that exist but are not defined in a evaluation context.

Method Summary

Modifier and Type	Method and Description
void	addVariable(String name, Object value) Adds a new named variable to this context.
boolean	getAllowPluginActivation() Returns whether this evaluation context supports plug-in activation.
Object	getDefaultVariable() Returns the default variable.
IEvaluationContext	getParent() Returns the parent context or null if this is the root of the evaluation context hierarchy.
IEvaluationContext	getRoot() Returns the root evaluation context.
Object	getVariable(String name) Returns the variable managed under the given name.
Object	removeVariable(String name) Removes the variable managed under the given name from this evaluation context.
Object	resolveVariable(String name, Object[] args) Resolves a variable for the given name and arguments.
void	setAllowPluginActivation(boolean value) Specifies whether this evaluation context allows activation of plug-ins for testers used in the expression tree.

Field Detail

UNDEFINED_VARIABLE

static final Object UNDEFINED_VARIABLE

Represents the value used by variables that exist but are not defined in a evaluation context. When tested by the 'with' expression, false will be returned.

Since:

3.4

Method Detail

getParent

IEvaluationContext getParent()

Returns the parent context or null if this is the root of the evaluation context hierarchy.

Returns:

the parent evaluation context or null

getRoot

IEvaluationContext getRoot()

Returns the root evaluation context.

Returns:

the root evaluation context

setAllowPluginActivation

void setAllowPluginActivation(boolean value)

Specifies whether this evaluation context allows activation of plug-ins for testers used in the expression tree. To actual trigger the plug-in loading this flag has to be set to true and the actual test expression must have the attribute forcePluginActivation set to true as well.

Parameters:

value - whether this evaluation context allows plug-in activation

Since:

3.2

getAllowPluginActivation

boolean getAllowPluginActivation()

Returns whether this evaluation context supports plug-in activation. If not set via setAllowPluginActivation(boolean) the parent value is returned. If no parent is set false is returned.

Returns:

whether plug-in activation is supported or not

Since:

3.2

getDefaultVariable

Object getDefaultVariable()

Returns the default variable.

Returns:

the default variable or null if no default variable is managed.

addVariable

void addVariable(String name,
                 Object value)

Adds a new named variable to this context. If a variable with the name already exists the new one overrides the existing one.

Parameters:

name - the variable's name

value - the variable's value

removeVariable

Object removeVariable(String name)

Removes the variable managed under the given name from this evaluation context.

Parameters:

name - the variable's name

Returns:

the currently stored value or null if the variable doesn't exist

getVariable

Object getVariable(String name)

Returns the variable managed under the given name.

Parameters:

name - the variable's name

Returns:

the variable's value or null if the content doesn't manage a variable with the given name

resolveVariable

Object resolveVariable(String name,
                       Object[] args)
                throws CoreException

Resolves a variable for the given name and arguments. This method can be used to dynamically resolve variable such as plug-in descriptors, resources, etc. The method is used by the resolve expression.

Parameters:

name - the variable to resolve

args - an object array of arguments used to resolve the variable

Returns:

the variable's value or null if no variable can be resolved for the given name and arguments

Throws:

CoreException - if an errors occurs while resolving the variable