QGIS API Documentation
3.0.2-Girona (307d082)
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Expression contexts are used to encapsulate the parameters around which a QgsExpression should be evaluated. More...
#include <qgsexpressioncontext.h>
Public Member Functions | |
QgsExpressionContext ()=default | |
Constructor for QgsExpressionContext. More... | |
QgsExpressionContext (const QList< QgsExpressionContextScope *> &scopes) | |
Initializes the context with given list of scopes. More... | |
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... | |
void | appendScopes (const QList< QgsExpressionContextScope *> &scopes) |
Appends a list of scopes to the end of the context. More... | |
QVariant | cachedValue (const QString &key) const |
Returns the matching cached value, if set. More... | |
void | clearCachedValues () const |
Clears all cached values from the context. More... | |
QString | description (const QString &name) const |
Returns a translated description string for the variable with specified name. 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... | |
QgsExpressionFunction * | 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 | hasCachedValue (const QString &key) const |
Returns true if the expression context contains a cached value with a matching key. More... | |
bool | hasFeature () const |
Returns true if the context has a feature associated with it. 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... | |
int | indexOfScope (const QString &scopeName) const |
Returns the index of the first scope with a matching name 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) |
QgsExpressionContext & | operator= (QgsExpressionContext &&other) noexcept |
QgsExpressionContextScope * | popScope () |
Removes the last scope from the expression context and return it. More... | |
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 | setCachedValue (const QString &key, const QVariant &value) const |
Sets a value to cache within the expression context. 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... | |
QList< QgsExpressionContextScope * > | takeScopes () |
Return all scopes from this context and remove them, leaving this context without any 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... | |
QVariantMap | variablesToMap () const |
Returns a map of variable name to value representing all the expression variables contained by the context. More... | |
Static Public Attributes | |
static const QString | EXPR_CLUSTER_COLOR |
Inbuilt variable name for cluster color variable. More... | |
static const QString | EXPR_CLUSTER_SIZE |
Inbuilt variable name for cluster size variable. More... | |
static const QString | EXPR_FIELDS |
Inbuilt variable name for fields storage. More... | |
static const QString | EXPR_GEOMETRY_PART_COUNT |
Inbuilt variable name for geometry part count variable. More... | |
static const QString | EXPR_GEOMETRY_PART_NUM |
Inbuilt variable name for geometry part number variable. More... | |
static const QString | EXPR_GEOMETRY_POINT_COUNT |
Inbuilt variable name for point count variable. More... | |
static const QString | EXPR_GEOMETRY_POINT_NUM |
Inbuilt variable name for point number variable. More... | |
static const QString | EXPR_ORIGINAL_VALUE |
Inbuilt variable name for value original value variable. More... | |
static const QString | EXPR_SYMBOL_ANGLE |
Inbuilt variable name for symbol angle variable. More... | |
static const QString | EXPR_SYMBOL_COLOR |
Inbuilt variable name for symbol color variable. More... | |
Expression contexts are used to encapsulate the parameters around which a QgsExpression should be evaluated.
QgsExpressions can then utilize 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.
See QgsExpressionContextUtils for helper methods for working with QgsExpressionContext objects.
Definition at line 375 of file qgsexpressioncontext.h.
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default |
Constructor for QgsExpressionContext.
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explicit |
Initializes the context with given list of scopes.
Ownership of the scopes is transferred to the stack.
Definition at line 228 of file qgsexpressioncontext.cpp.
QgsExpressionContext::QgsExpressionContext | ( | const QgsExpressionContext & | other | ) |
Copy constructor.
Definition at line 233 of file qgsexpressioncontext.cpp.
QgsExpressionContext::~QgsExpressionContext | ( | ) |
Definition at line 271 of file qgsexpressioncontext.cpp.
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.
name | variable name |
Definition at line 327 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.
name | variable name |
Definition at line 314 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.
scope | expression context to append to context |
Definition at line 459 of file qgsexpressioncontext.cpp.
void QgsExpressionContext::appendScopes | ( | const QList< QgsExpressionContextScope *> & | scopes | ) |
Appends a list of scopes to the end of the context.
This scopes will override any matching variables or functions provided by existing scopes within the context. Ownership of the scopes is transferred to the stack.
scopes | scopes to append to context |
Definition at line 464 of file qgsexpressioncontext.cpp.
QVariant QgsExpressionContext::cachedValue | ( | const QString & | key | ) | const |
Returns the matching cached value, if set.
This can be used to retrieve the previously stored results of an expensive expression sub-calculation.
key | unique key used to store cached value |
Definition at line 553 of file qgsexpressioncontext.cpp.
void QgsExpressionContext::clearCachedValues | ( | ) | const |
Clears all cached values from the context.
Definition at line 558 of file qgsexpressioncontext.cpp.
QString QgsExpressionContext::description | ( | const QString & | name | ) | const |
Returns a translated description string for the variable with specified name.
If no specific description has been provided for the variable, the value from QgsExpression::variableHelpText() will be returned.
Definition at line 413 of file qgsexpressioncontext.cpp.
QgsFeature QgsExpressionContext::feature | ( | ) | const |
Convenience function for retrieving the feature for the context, if set.
Definition at line 508 of file qgsexpressioncontext.cpp.
QgsFields QgsExpressionContext::fields | ( | ) | const |
Convenience function for retrieving the fields for the context, if set.
Definition at line 529 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.
Definition at line 387 of file qgsexpressioncontext.cpp.
QgsExpressionFunction * 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.
name | function name |
Definition at line 441 of file qgsexpressioncontext.cpp.
QStringList QgsExpressionContext::functionNames | ( | ) | const |
Retrieves a list of function names contained in the context.
Definition at line 429 of file qgsexpressioncontext.cpp.
bool QgsExpressionContext::hasCachedValue | ( | const QString & | key | ) | const |
Returns true if the expression context contains a cached value with a matching key.
key | unique key used to store cached value |
Definition at line 548 of file qgsexpressioncontext.cpp.
bool QgsExpressionContext::hasFeature | ( | ) | const |
Returns true if the context has a feature associated with it.
Definition at line 498 of file qgsexpressioncontext.cpp.
bool QgsExpressionContext::hasFunction | ( | const QString & | name | ) | const |
Checks whether a specified function is contained in the context.
name | function name |
Definition at line 419 of file qgsexpressioncontext.cpp.
bool QgsExpressionContext::hasVariable | ( | const QString & | name | ) | const |
Check whether a variable is specified by any scope within the context.
name | variable name |
Definition at line 277 of file qgsexpressioncontext.cpp.
int QgsExpressionContext::indexOfScope | ( | QgsExpressionContextScope * | scope | ) | const |
Returns the index of the specified scope if it exists within the context.
scope | scope to find |
Definition at line 356 of file qgsexpressioncontext.cpp.
int QgsExpressionContext::indexOfScope | ( | const QString & | scopeName | ) | const |
Returns the index of the first scope with a matching name within the context.
scopeName | name of scope to find |
Definition at line 364 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.
name | variable name |
Definition at line 304 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.
name | variable name |
Definition at line 403 of file qgsexpressioncontext.cpp.
QgsExpressionContextScope * QgsExpressionContext::lastScope | ( | ) |
Returns the last scope added to the context.
Definition at line 348 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 484 of file qgsexpressioncontext.cpp.
QgsExpressionContext & QgsExpressionContext::operator= | ( | const QgsExpressionContext & | other | ) |
Definition at line 258 of file qgsexpressioncontext.cpp.
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noexcept |
Definition at line 243 of file qgsexpressioncontext.cpp.
QgsExpressionContextScope * QgsExpressionContext::popScope | ( | ) |
Removes the last scope from the expression context and return it.
Definition at line 469 of file qgsexpressioncontext.cpp.
QgsExpressionContextScope * QgsExpressionContext::scope | ( | int | index | ) |
Returns the scope at the specified index within the context.
index | index of scope |
Definition at line 340 of file qgsexpressioncontext.cpp.
int QgsExpressionContext::scopeCount | ( | ) | const |
Returns the number of scopes contained in the context.
Definition at line 454 of file qgsexpressioncontext.cpp.
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inline |
Returns a list of scopes contained within the stack.
Definition at line 481 of file qgsexpressioncontext.h.
void QgsExpressionContext::setCachedValue | ( | const QString & | key, |
const QVariant & | value | ||
) | const |
Sets a value to cache within the expression context.
This can be used to cache the results of expensive expression sub-calculations, to speed up future evaluations using the same expression context.
key | unique key for retrieving cached value |
value | value to cache |
Definition at line 543 of file qgsexpressioncontext.cpp.
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.
feature | feature for context |
Definition at line 490 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.
fields | fields for context |
Definition at line 521 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.
variableNames | variable names to highlight |
Definition at line 309 of file qgsexpressioncontext.cpp.
void QgsExpressionContext::setOriginalValueVariable | ( | const QVariant & | value | ) |
Sets the original value variable value for the context.
value | value for original value variable. This usually represents the an original widget value before any data defined overrides have been applied. |
Definition at line 534 of file qgsexpressioncontext.cpp.
QList< QgsExpressionContextScope * > QgsExpressionContext::takeScopes | ( | ) |
Return all scopes from this context and remove them, leaving this context without any context.
Ownership is transferred to the caller.
Definition at line 477 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.
name | variable name |
Definition at line 287 of file qgsexpressioncontext.cpp.
QStringList QgsExpressionContext::variableNames | ( | ) | const |
Returns a list of variables names set by all scopes in the context.
Definition at line 377 of file qgsexpressioncontext.cpp.
QVariantMap QgsExpressionContext::variablesToMap | ( | ) | const |
Returns a map of variable name to value representing all the expression variables contained by the context.
Definition at line 293 of file qgsexpressioncontext.cpp.
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Inbuilt variable name for cluster color variable.
Definition at line 711 of file qgsexpressioncontext.h.
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Inbuilt variable name for cluster size variable.
Definition at line 709 of file qgsexpressioncontext.h.
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Inbuilt variable name for fields storage.
Definition at line 693 of file qgsexpressioncontext.h.
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Inbuilt variable name for geometry part count variable.
Definition at line 701 of file qgsexpressioncontext.h.
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Inbuilt variable name for geometry part number variable.
Definition at line 703 of file qgsexpressioncontext.h.
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Inbuilt variable name for point count variable.
Definition at line 705 of file qgsexpressioncontext.h.
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Inbuilt variable name for point number variable.
Definition at line 707 of file qgsexpressioncontext.h.
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Inbuilt variable name for value original value variable.
Definition at line 695 of file qgsexpressioncontext.h.
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Inbuilt variable name for symbol angle variable.
Definition at line 699 of file qgsexpressioncontext.h.
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Inbuilt variable name for symbol color variable.
Definition at line 697 of file qgsexpressioncontext.h.