Class: QgsAbstractValidityCheck

Abstract base class for individual validity checks.

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().

See also

QgsValidityCheckRegistry

Added in version 3.6.

Note

This is an abstract class, with methods which must be implemented by a subclass.

The following methods must be implemented: checkType(), create(), id(), runCheck()

Enums

Type

Check types

Abstract Methods

checkType

Returns the type of the check.

create

Creates a new instance of the check and returns it.

id

Returns the unique ID of the check.

runCheck

Runs the check and returns a list of results.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsAbstractValidityCheck. See the FAQ for more details.

prepareCheck

Prepares the check for execution, and returns True if the check can be run.
class qgis.core.QgsAbstractValidityCheck[source]

Bases: object

class Type(*values)

Bases: IntEnum

Check types

  • LayoutCheck: Print layout validity check, triggered on exporting a print layout

    Available as QgsAbstractValidityCheck.TypeLayoutCheck in older QGIS releases.

  • UserCheck: Starting point for custom user types

    Available as QgsAbstractValidityCheck.TypeUserCheck in older QGIS releases.

abstract checkType(self) → int[source]

Returns the type of the check.

Return type:

int

abstract create(self) → QgsAbstractValidityCheck | None[source]

Creates a new instance of the check and returns it.

Return type:

Optional[QgsAbstractValidityCheck]

abstract id(self) → str[source]

Returns the unique ID of the check.

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

Return type:

str

virtual prepareCheck(self, context: QgsValidityCheckContext | None, feedback: QgsFeedback | None) → bool[source]

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.

Parameters:
Return type:

bool

abstract runCheck(self, context: QgsValidityCheckContext | None, feedback: QgsFeedback | None) → List[QgsValidityCheckResult]

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.

Parameters:
Return type:

List[QgsValidityCheckResult]