Class: QgsMapCanvasTracer¶

Extension of QgsTracer that provides extra functionality.

This tracer subclass adds:

automatic updates of own configuration based on canvas settings
reporting of issues to the user via message bar
determines whether tracing is currently enabled by the user

A simple registry of tracer instances associated to map canvas instances is kept for convenience. (Map tools do not need to create their local tracer instances and map canvas API is not “polluted” by this optional functionality).

Class Hierarchy¶

Base classes¶

`QgsTracer`	Utility class that constructs a planar graph from the input vector layers and provides shortest path search for tracing of existing features.
QObject

Methods

`actionEnableSnapping`	Access to action that user may use to toggle snapping on/off.
`actionEnableTracing`	Access to action that user may use to toggle tracing on/off.
`reportError`	Report a path finding error to the user
`setActionEnableSnapping`	Assign "enable snapping" checkable action to the tracer.
`setActionEnableTracing`	Assign "enable tracing" checkable action to the tracer.

Virtual Methods

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

configure

Sets configuration from current snapping settings and canvas settings

Static Methods

tracerForCanvas

Retrieve instance of this class associated with given canvas (if any).

class qgis.gui.QgsMapCanvasTracer[source]¶

Bases: QgsTracer

__init__(canvas: QgsMapCanvas | None, messageBar: QgsMessageBar | None = None)

Create tracer associated with a particular map canvas, optionally message bar for reporting

Parameters:

canvas (Optional[QgsMapCanvas])
messageBar (Optional[QgsMessageBar] = None)

actionEnableSnapping(self) → QAction | None[source]¶

Access to action that user may use to toggle snapping on/off. May be None if no action was associated.

Return type:: Optional[QAction]

actionEnableTracing(self) → QAction | None[source]¶

Access to action that user may use to toggle tracing on/off. May be None if no action was associated

Return type:: Optional[QAction]

virtual configure(self)[source]¶: Sets configuration from current snapping settings and canvas settings

reportError(self, err: QgsTracer.PathError, addingVertex: bool)[source]¶

Report a path finding error to the user

Parameters:

err (QgsTracer.PathError)
addingVertex (bool)

setActionEnableSnapping(self, action: QAction | None)[source]¶

Assign “enable snapping” checkable action to the tracer. The action is used to determine whether snapping is currently enabled by the user.

Parameters:: action (Optional[QAction])

setActionEnableTracing(self, action: QAction | None)[source]¶

Assign “enable tracing” checkable action to the tracer. The action is used to determine whether tracing is currently enabled by the user

Parameters:: action (Optional[QAction])

static tracerForCanvas(canvas: QgsMapCanvas | None) → QgsMapCanvasTracer | None[source]¶

Retrieve instance of this class associated with given canvas (if any). The class keeps a simple registry of tracers associated with map canvas instances for easier access to the common tracer by various map tools

Parameters:: canvas (Optional[QgsMapCanvas])
Return type:: Optional[QgsMapCanvasTracer]