I want to know how to check for a mouse click in QGIS. I am trying to write a Python plugin and want to provide functionality similar to the "Select Single Feature" tool that already exists in QGIS.
I checked the QGIS API docs and found
QgsMapCanvas::CanvasProperties::mouseButtonDown
This sounds promising. I have a QgsMapCanvas object but I can't see how to access the mouseButtonDown attribute.
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)
class PointTool(QgsMapTool): NameError: name 'QgsMapTool' is not defined. Any ideas?
from qgis.gui import QgsMapTool at the top
None. I would save what the user had selected using QgsMapCanvas.mapTool() restoring it after you are done.
I think you can do this with a combination of using QGIS "canvasClicked" but also SIGNAL/SLOTS to deal with the response:
result = QObject.connect(self.clickTool, SIGNAL("canvasClicked(const QgsPoint &, Qt::MouseButton)"), self.handleMouseDown)
Not tried but should give you some more information to start looking at. There is a tutorial here where someone is using this to build a very basic plugin.
QgsMapToolEmitPoint class which will give you the basic start for a tool. A good way to connect to signals in PyQt is using this syntax self.clickTool.canvasClicked.connect(self.handleMouseDown)
Try something like this (this is to select a point):
def run(self):
self.pointEmitter = QgsMapToolEmitPoint(self.iface.mapCanvas())
QObject.connect( self.pointEmitter, SIGNAL("canvasClicked(const QgsPoint, Qt::MouseButton)"), self.selectNow)
self.iface.mapCanvas().setMapTool( self.pointEmitter )
def selectNow(self, point, button):
#QMessageBox.information(None, "Clicked coords", " x: " + str(point.x()) + " Y: " + str(point.y()) )
layer = self.iface.activeLayer()
if not layer or layer.type() != QgsMapLayer.VectorLayer:
QMessageBox.warning(None, "No!", "Select a vector layer")
return
width = self.iface.mapCanvas().mapUnitsPerPixel() * 2
rect = QgsRectangle(point.x() - width,
point.y() - width,
point.x() + width,
point.y() + width)
rect = self.iface.mapCanvas().mapRenderer().mapToLayerCoordinates(layer, rect)
layer.select([], rect)
feat = QgsFeature()
ids = []
while layer.nextFeature(feat):
ids.append( feat.id() )
layer.setSelectedFeatures( ids )
self.clickTool.canvasClicked.connect(self.handleMouseDown) syntax to connect to signals as it's much cleaner.