PyQGIS – Select Features by Mouse Click Not Working

pyqgis-3qgis-3qgis-plugins

I'm using the solution provided in this question. but when I click on the canvas nothing happens. here is my code

from qgis.gui import QgsMapToolIdentifyFeature, QgsMapToolIdentify
from qgis.core import (
    Qgis, QgsVectorLayer
)

class selectTool(QgsMapToolIdentifyFeature):

        def __init__(self, iface, layer):
            self.iface = iface
            self.canvas = self.iface.mapCanvas()
            self.layer = layer
            QgsMapToolIdentifyFeature.__init__(self, self.canvas, self.layer)
            self.iface.currentLayerChanged.connect(self.active_changed)
            
        def active_changed(self, layer):
            self.layer.removeSelection()
            if isinstance(layer, QgsVectorLayer) and layer.isSpatial():
                self.layer = layer
                self.setLayer(self.layer)
                
        def canvasPressEvent(self, event):
            found_features = self.identify(event.x(), event.y(), [self.layer], QgsMapToolIdentify.TopDownAll)
            print(found_features)
            self.layer.selectByIds([f.mFeature.id() for f in found_features], QgsVectorLayer.AddToSelection)
            
        def deactivate(self):
            self.layer.removeSelection()

And here is the code that instantiates this class, it is a function that is called when I push a button on my plugin, I have confirmed that the button push is tied to this function by using this print statement. after the button is pushed I can click in the canvas on features but no feature is selected, I have also confirmed that the correct layer is selected.

    def start_line_edit(self):
        print("button pushed")
        t = selectTool(iface, self.poly_layer)
        iface.mapCanvas().setMapTool(t)

Best Answer

For me, the instance of selectTool is deleted at the end of the start_line_edit function.

So try :

def start_line_edit(self):
    print("button pushed")
    self.t = selectTool(iface, self.poly_layer)
    iface.mapCanvas().setMapTool(self.t)

Related Solutions

PyQGIS – Programmatically Check for Mouse Click in PyQGIS

The best way to make a new tool like the Select Single Feature tool is to inherit from the QgsMapTool class. When your tool is active, which can be set using QgsMapCanvas::setMapTool, any keyboard or click events the canvas gets will be passed onto your custom tool.

Here is a basic QgsMapTool class

class PointTool(QgsMapTool):   
    def __init__(self, canvas):
        QgsMapTool.__init__(self, canvas)
        self.canvas = canvas    

    def canvasPressEvent(self, event):
        pass

    def canvasMoveEvent(self, event):
        x = event.pos().x()
        y = event.pos().y()

        point = self.canvas.getCoordinateTransform().toMapCoordinates(x, y)

    def canvasReleaseEvent(self, event):
        #Get the click
        x = event.pos().x()
        y = event.pos().y()

        point = self.canvas.getCoordinateTransform().toMapCoordinates(x, y)

    def activate(self):
        pass

    def deactivate(self):
        pass

    def isZoomTool(self):
        return False

    def isTransient(self):
        return False

    def isEditTool(self):
        return True

You can do what you need in canvasReleaseEvent, etc

To set this tool active you just do:

tool = PointTool(qgis.iface.mapCanvas())
qgis.iface.mapCanvas().setMapTool(tool)

[GIS] Getting coordinates from mouse click in QGIS 3 (python plugin)

I have a little bit of a hard time getting the "canvasReleaseEvent" to return the x,y coordinates. At the moment i am writing my code into that function since it does output the x, y. (simply by stating "x=point.x()" etc).

I think i will try @xunilk's code and see if that would be easier.

https://webgeodatavore.github.io/pyqgis-samples/gui-group/QgsMapTool.html

# coding: utf-8
from PyQt4.QtCore import Qt
from qgis.gui import QgsMapTool
from qgis.utils import iface


class SendPointToolCoordinates(QgsMapTool):
    """ Enable to return coordinates from clic in a layer.
    """
    def __init__(self, canvas, layer):
        """ Constructor.
        """
        QgsMapTool.__init__(self, canvas)
        self.canvas = canvas
        self.layer = layer
        self.setCursor(Qt.CrossCursor)

    def canvasReleaseEvent(self, event):
        point = self.toLayerCoordinates(self.layer, event.pos())

        print(point.x(), point.y())

layer, canvas = iface.activeLayer(), iface.mapCanvas()

send_point_tool_coordinates = SendPointToolCoordinates(
    canvas,
    layer
)
canvas.setMapTool(send_point_tool_coordinates)

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