Expression contexts are used to encapsulate the parameters around which a QgsExpression should be evaluated. More...

#include <qgsexpressioncontext.h>

Public Member Functions
	QgsExpressionContext ()

	QgsExpressionContext (const QgsExpressionContext &other)
	Copy constructor. More...

	~QgsExpressionContext ()

QgsExpressionContextScope *	activeScopeForVariable (const QString &name)
	Returns the currently active scope from the context for a specified variable name. More...

const QgsExpressionContextScope *	activeScopeForVariable (const QString &name) const
	Returns the currently active scope from the context for a specified variable name. More...

void	appendScope (QgsExpressionContextScope *scope)
	Appends a scope to the end of the context. More...

QgsFeature	feature () const
	Convenience function for retrieving the feature for the context, if set. More...

QgsFields	fields () const
	Convenience function for retrieving the fields for the context, if set. More...

QStringList	filteredVariableNames () const
	Returns a filtered list of variables names set by all scopes in the context. More...

QgsExpression::Function *	function (const QString &name) const
	Fetches a matching function from the context. More...

QStringList	functionNames () const
	Retrieves a list of function names contained in the context. More...

bool	hasFunction (const QString &name) const
	Checks whether a specified function is contained in the context. More...

bool	hasVariable (const QString &name) const
	Check whether a variable is specified by any scope within the context. More...

int	indexOfScope (QgsExpressionContextScope *scope) const
	Returns the index of the specified scope if it exists within the context. More...

bool	isHighlightedVariable (const QString &name) const
	Returns true if the specified variable name is intended to be highlighted to the user. More...

bool	isReadOnly (const QString &name) const
	Returns whether a variable is read only, and should not be modifiable by users. More...

QgsExpressionContextScope *	lastScope ()
	Returns the last scope added to the context. More...

QgsExpressionContext &	operator<< (QgsExpressionContextScope *scope)
	Appends a scope to the end of the context. More...

QgsExpressionContext &	operator= (const QgsExpressionContext &other)

QgsExpressionContextScope *	scope (int index)
	Returns the scope at the specified index within the context. More...

int	scopeCount () const
	Returns the number of scopes contained in the context. More...

QList< QgsExpressionContextScope * >	scopes ()
	Returns a list of scopes contained within the stack. More...

void	setFeature (const QgsFeature &feature)
	Convenience function for setting a feature for the context. More...

void	setFields (const QgsFields &fields)
	Convenience function for setting a fields for the context. More...

void	setHighlightedVariables (const QStringList &variableNames)
	Sets the list of variable names within the context intended to be highlighted to the user. More...

void	setOriginalValueVariable (const QVariant &value)
	Sets the original value variable value for the context. More...

QVariant	variable (const QString &name) const
	Fetches a matching variable from the context. More...

QStringList	variableNames () const
	Returns a list of variables names set by all scopes in the context. More...

Static Public Attributes
static const QString	EXPR_FEATURE

static const QString	EXPR_FIELDS

static const QString	EXPR_ORIGINAL_VALUE

Detailed Description

Expression contexts are used to encapsulate the parameters around which a QgsExpression should be evaluated.

QgsExpressions can then utilise the information stored within a context to contextualise their evaluated result. A QgsExpressionContext consists of a stack of QgsExpressionContextScope objects, where scopes added later to the stack will override conflicting variables and functions from scopes lower in the stack.

Note: added in QGIS 2.12

Definition at line 239 of file qgsexpressioncontext.h.

Constructor & Destructor Documentation

QgsExpressionContext::QgsExpressionContext ( )

inline

Definition at line 243 of file qgsexpressioncontext.h.

QgsExpressionContext::QgsExpressionContext ( const QgsExpressionContext & other )

Copy constructor.

Definition at line 201 of file qgsexpressioncontext.cpp.

QgsExpressionContext::~QgsExpressionContext ( )

Definition at line 222 of file qgsexpressioncontext.cpp.

Member Function Documentation

QgsExpressionContextScope * QgsExpressionContext::activeScopeForVariable ( const QString & name )

Returns the currently active scope from the context for a specified variable name.

As scopes later in the stack override earlier contexts, this will be the last matching scope which contains a matching variable.

Parameters

name	variable name

Returns: matching scope containing variable, or null if none found

Definition at line 267 of file qgsexpressioncontext.cpp.

const QgsExpressionContextScope * QgsExpressionContext::activeScopeForVariable ( const QString & name ) const

Returns the currently active scope from the context for a specified variable name.

As scopes later in the stack override earlier contexts, this will be the last matching scope which contains a matching variable.

Parameters

name	variable name

Returns: matching scope containing variable, or null if none found

Definition at line 254 of file qgsexpressioncontext.cpp.

void QgsExpressionContext::appendScope ( QgsExpressionContextScope * scope )

Appends a scope to the end of the context.

This scope will override any matching variables or functions provided by existing scopes within the context. Ownership of the scope is transferred to the stack.

Parameters

scope expression context to append to context

Definition at line 380 of file qgsexpressioncontext.cpp.

QgsFeature QgsExpressionContext::feature ( ) const

Convenience function for retrieving the feature for the context, if set.

See also: setFeature

Definition at line 399 of file qgsexpressioncontext.cpp.

QgsFields QgsExpressionContext::fields ( ) const

Convenience function for retrieving the fields for the context, if set.

See also: setFields

Definition at line 412 of file qgsexpressioncontext.cpp.

QStringList QgsExpressionContext::filteredVariableNames ( ) const

Returns a filtered list of variables names set by all scopes in the context.

The included variables are those which should be seen by users.

Returns: filtered list of unique variable names

See also: variableNames

Definition at line 314 of file qgsexpressioncontext.cpp.

QgsExpression::Function * QgsExpressionContext::function ( const QString & name ) const

Fetches a matching function from the context.

The function will be fetched from the last scope contained within the context which has a matching function set.

Parameters

name	function name

Returns: function if contained by the context, otherwise null.

See also: hasFunction

Definition at line 362 of file qgsexpressioncontext.cpp.

QStringList QgsExpressionContext::functionNames ( ) const

Retrieves a list of function names contained in the context.

See also: function(); variableNames()

Definition at line 350 of file qgsexpressioncontext.cpp.

bool QgsExpressionContext::hasFunction ( const QString & name ) const

Checks whether a specified function is contained in the context.

Parameters

name	function name

Returns: true if context provides a matching function

See also: function

Definition at line 340 of file qgsexpressioncontext.cpp.

bool QgsExpressionContext::hasVariable ( const QString & name ) const

Check whether a variable is specified by any scope within the context.

Parameters

name	variable name

Returns: true if variable is set

See also: variable(); variableNames()

Definition at line 228 of file qgsexpressioncontext.cpp.

int QgsExpressionContext::indexOfScope ( QgsExpressionContextScope * scope ) const

Returns the index of the specified scope if it exists within the context.

Parameters

scope scope to find

Returns: index of scope, or -1 if scope was not found within the context.

Definition at line 296 of file qgsexpressioncontext.cpp.

bool QgsExpressionContext::isHighlightedVariable ( const QString & name ) const

Returns true if the specified variable name is intended to be highlighted to the user.

This is used by the expression builder to more prominently display the variable.

Parameters

name	variable name

See also: setHighlightedVariables()

Definition at line 244 of file qgsexpressioncontext.cpp.

bool QgsExpressionContext::isReadOnly ( const QString & name ) const

Returns whether a variable is read only, and should not be modifiable by users.

Parameters

name	variable name

Returns: true if variable is read only. Read only status will be taken from last matching scope which contains a matching variable.

Definition at line 330 of file qgsexpressioncontext.cpp.

QgsExpressionContextScope * QgsExpressionContext::lastScope ( )

Returns the last scope added to the context.

See also: scope()

Definition at line 288 of file qgsexpressioncontext.cpp.

QgsExpressionContext & QgsExpressionContext::operator<< ( QgsExpressionContextScope * scope )

Appends a scope to the end of the context.

This scope will override any matching variables or functions provided by existing scopes within the context. Ownership of the scope is transferred to the stack.

Definition at line 385 of file qgsexpressioncontext.cpp.

QgsExpressionContext & QgsExpressionContext::operator= ( const QgsExpressionContext & other )

Definition at line 210 of file qgsexpressioncontext.cpp.

QgsExpressionContextScope * QgsExpressionContext::scope ( int index )

Returns the scope at the specified index within the context.

Parameters

index index of scope

Returns: matching scope, or null if none found

See also: lastScope()

Definition at line 280 of file qgsexpressioncontext.cpp.

int QgsExpressionContext::scopeCount ( ) const

Returns the number of scopes contained in the context.

Definition at line 375 of file qgsexpressioncontext.cpp.

QList< QgsExpressionContextScope* > QgsExpressionContext::scopes ( )

inline

Returns a list of scopes contained within the stack.

Returns: list of pointers to scopes

Definition at line 317 of file qgsexpressioncontext.h.

void QgsExpressionContext::setFeature ( const QgsFeature & feature )

Convenience function for setting a feature for the context.

The feature will be set within the last scope of the context, so will override any existing features within the context.

Parameters

feature feature for context

See also: feature()

Definition at line 391 of file qgsexpressioncontext.cpp.

void QgsExpressionContext::setFields ( const QgsFields & fields )

Convenience function for setting a fields for the context.

The fields will be set within the last scope of the context, so will override any existing fields within the context.

Parameters

fields fields for context

See also: fields()

Definition at line 404 of file qgsexpressioncontext.cpp.

void QgsExpressionContext::setHighlightedVariables ( const QStringList & variableNames )

Sets the list of variable names within the context intended to be highlighted to the user.

This is used by the expression builder to more prominently display these variables.

Parameters

variableNames variable names to highlight

See also: isHighlightedVariable()

Definition at line 249 of file qgsexpressioncontext.cpp.

void QgsExpressionContext::setOriginalValueVariable ( const QVariant & value )

Sets the original value variable value for the context.

Parameters

value value for original value variable. This usually represents the an original widget value before any data defined overrides have been applied.

Note: added in QGIS 2.12

Definition at line 417 of file qgsexpressioncontext.cpp.

QVariant QgsExpressionContext::variable ( const QString & name ) const

Fetches a matching variable from the context.

The variable will be fetched from the last scope contained within the context which has a matching variable set.

Parameters

name	variable name

Returns: variable value if matching variable exists in the context, otherwise an invalid QVariant

See also: hasVariable(); variableNames()

Definition at line 238 of file qgsexpressioncontext.cpp.

QStringList QgsExpressionContext::variableNames ( ) const

Returns a list of variables names set by all scopes in the context.

Returns: list of unique variable names

See also: filteredVariableNames; functionNames; hasVariable; variable

Definition at line 304 of file qgsexpressioncontext.cpp.

Member Data Documentation

const QString QgsExpressionContext::EXPR_FEATURE

static

Definition at line 421 of file qgsexpressioncontext.h.

const QString QgsExpressionContext::EXPR_FIELDS

static

Definition at line 420 of file qgsexpressioncontext.h.

const QString QgsExpressionContext::EXPR_ORIGINAL_VALUE

static

Definition at line 422 of file qgsexpressioncontext.h.

The documentation for this class was generated from the following files:

/tmp/buildd/qgis-2.12.0+99unstable/src/core/qgsexpressioncontext.h
/tmp/buildd/qgis-2.12.0+99unstable/src/core/qgsexpressioncontext.cpp

Public Member Functions

Static Public Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation