QgsAbstractValidityCheck class

Abstract base class for individual validity checks.

Contents

Validity checks represent objects which can run a test using a QgsValidityCheckContext, and return the results of the check via QgsValidityCheckResult objects.

Checks can be used for many different use cases, e.g. validating a layout's contents before allowing an export to occur, or validating the contents of a Processing model (and warning if required plugin based providers are not available or if compulsory algorithm parameters have not been populated).

Subclasses must indicate the type of check they represent via the checkType() method. When checks are performed, all the registered checks with a matching check type are performed sequentially. The check type also dictates the subclass of the QgsValidityCheckContext which is given to the subclass' runCheck method.

Checks must be registered in the application's QgsValidityCheckRegistry, which is accessible via QgsApplication::validityCheckRegistry().

Public types

enum Type { TypeLayoutCheck = 0, TypeUserCheck = 10000 }
Check types.

Public functions

auto checkType() const -> int pure virtual
Returns the type of the check.
auto create() const -> QgsAbstractValidityCheck* pure virtual
Creates a new instance of the check and returns it.
auto id() const -> QString pure virtual
Returns the unique ID of the check.
auto prepareCheck(const QgsValidityCheckContext* context, QgsFeedback* feedback) -> bool virtual
Prepares the check for execution, and returns true if the check can be run.
auto runCheck(const QgsValidityCheckContext* context, QgsFeedback* feedback) -> QList<QgsValidityCheckResult> pure virtual
Runs the check and returns a list of results.

Enum documentation

enum QgsAbstractValidityCheck::Type

Check types.

Enumerators
TypeLayoutCheck

Print layout validity check, triggered on exporting a print layout.
TypeUserCheck

Starting point for custom user types.

Function documentation

QString QgsAbstractValidityCheck::id() const pure virtual

Returns the unique ID of the check.

This is a non-translated, non-user visible string identifying the check.

bool QgsAbstractValidityCheck::prepareCheck(const QgsValidityCheckContext* context, QgsFeedback* feedback) virtual

Prepares the check for execution, and returns true if the check can be run.

This method is always called from the main thread, and subclasses can implement it to do preparatory steps which are not thread safe (e.g. obtaining feature sources from vector layers). It is followed by a call to runCheck(), which may be performed in a background thread.

Individual calls to prepareCheck()/runCheck() are run on a new instance of the check (see create()), so subclasses can safely store state from the prepareCheck() method ready for the subsequent runCheck() method.

The context argument gives the wider in which the check is being run.

QList<QgsValidityCheckResult> QgsAbstractValidityCheck::runCheck(const QgsValidityCheckContext* context, QgsFeedback* feedback) pure virtual

Runs the check and returns a list of results.

If the check is "passed" and no warnings or errors are generated, then an empty list should be returned.

This method may be called in a background thread, so subclasses should take care to ensure that only thread-safe methods are used. It is always preceded by a call to prepareCheck().

If a check needs to perform non-thread-safe tests, these should be implemented within prepareCheck() and stored in the subclass instance to be returned by this method.

The context argument gives the wider in which the check is being run.