[GIS] How to define an event for features selected in mapcanvas in qgis using python

pyqgisqgisqgis-plugins

I have created a push button, when it is clicked it calls the function 'selectfeatures'. This function will call the Select feature by free hand tool of QGIS and allows the user to select features in the mapcanvas. What I need is my event to recognize the features selected in mapcanvas and call another function. How should this be accomplished?

Best Answer

If I got you right, you can use the SIGNAL selectionChanged from your vector layer and connect it to your other function (which must accept an argument to receive selected features' ids).

For example, load a vector layer to QGIS, activate it in the ToC and run the following code in the QGIS Python console. You should see the function is running after a new selection, recognizing the selected features' ids.

lyr=iface.activeLayer()
def myFunction(selFeatures):
    print str(len(selFeatures)) + " features were selected: " + str(selFeatures)

lyr.selectionChanged.connect(myFunction)

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[GIS] How to filter the MouseWheel event in a QGIS C++ plugin

This code should do what you need:

from PyQt4.QtCore import QEvent, QObject
from PyQt4.QtGui import QWheelEvent
from qgis.gui import QgsMapCanvas
from qgis.core import QgsMessageLog
import qgis

class EventHook(QObject):
  def eventFilter(self, object, event):
    if event.type() == QEvent.Wheel:
      QgsMessageLog.logMessage("Wheel event delta was %s" % event.delta(),"plugin")
      return True
    else:
      return False

hook = EventHook()
qgis.utils.iface.mapCanvas().viewport().installEventFilter(hook)

I would be careful how you use this as you are changing how QGIS behaves.

Like @dakcarto said, a better method is to popup a dialog, or widget, that grabs mouse wheel focus to adjust the required value.

Make sure you clean up using qgis.utils.iface.mapCanvas().viewport().removeEventFilter(hook)

[GIS] Triggering QGIS action when plugin button is clicked

You don't really seem to have read at least one of the resources I collected for you in Layer properties dialog in my QGIS plugin.

If you open, for example this one, you'll see the answer to your question:

button.clicked.connect(self.onClicked)

In your case it would be something like (you might need to edit it to match your plugin structure):

self.areapushbutton.clicked.connect( self.iface.actionSelectFreehand().trigger )

Best Answer

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