使用PyQgis选择和缩放图层的要素

Question

I want to select features and to zoom on them and do all these steps using PyQgis.

And I'm able to do both of them separatly but it doesn't seems to work when I try to mix the two of them.

Both of the codes I use for them are from the internet. Here's what I use to select features of a layer :

from qgis.core import *
import qgis.utils
lyrMap = QgsVectorLayer('C:/someplace', 'MapName', 'ogr')
QgsMapLayerRegistry.instance().addMapLayer(lyrMap)

expr = QgsExpression("'Attribute' IS NOT NULL")
it = lyrMap.getFeatures(QgsFeatureRequest(expr))
ids = [i.id() for i in it] #select only the features for which the expression is true
lyrMap.setSelectedFeatures(ids)

And it seems to do the trick as features appear selected on QGis.

In order to zoom the code is much more simple, it's just :

canvas = qgis.utils.iface.mapCanvas()
canvas.zoomToSelected(lyrMap)

But it seems that canvas doesn't consider that there's a selection on lyrMap and simply do nothing. I've tried to do the selection manually in QGis, and then zoom using zoomToSelected, and it worked.

But my objective is to do it without needing to do the selection manually...

Note : I don't think that's the issue, but the attribute I'm doing the selection on is from a join between lyrMap and another layer (I didn't put the code here because I don't think it's linked).

Thanks in advances for answers, clues or anything really :) !

Answer 1

This is working for my plugin. I am using python 2.7 and QGIS 1.8 and 2.0.1.You can use this code after including using vector file and adding it to the registry.

self.rubberBand = None
#create vertex marker for point..older versons..
self.vMarker = None
#add rubberbands 
self.crossRb = QgsRubberBand(iface.mapCanvas(),QGis.Line)
self.crossRb.setColor(Qt.black)


def pan(self):
        print "pan button clicked!"
        x = self.dlg.ui.mTxtX.text()
        y = self.dlg.ui.mTxtY.text()
        if not x:
            return
        if not y:
            return
        print x + "," + y
        canvas = self.canvas
        currExt = canvas.extent()
        canvasCenter = currExt.center()
        dx = float(x) - canvasCenter.x()
        dy = float(y) - canvasCenter.y()
        xMin = currExt.xMinimum() + dx
        xMax = currExt.xMaximum() + dx
        yMin = currExt.yMinimum() + dy
        yMax = currExt.yMaximum() + dy
        newRect = QgsRectangle(xMin,yMin,xMax,yMax)
        canvas.setExtent(newRect)
        pt = QgsPoint(float(x),float(y))
        self.zoom(pt)
        canvas.refresh()

def zoom(self,point):
        canvas = self.canvas
        currExt = canvas.extent()
        leftPt = QgsPoint(currExt.xMinimum(),point.y())
        rightPt = QgsPoint(currExt.xMaximum(),point.y())
        topPt = QgsPoint(point.x(),currExt.yMaximum())
        bottomPt = QgsPoint(point.x(),currExt.yMinimum())
        horizLine = QgsGeometry.fromPolyline( [ leftPt , rightPt ] )
        vertLine = QgsGeometry.fromPolyline( [ topPt , bottomPt ] )
        self.crossRb.reset(QGis.Line)
        self.crossRb.addGeometry(horizLine,None)
        self.crossRb.addGeometry(vertLine,None)
        if QGis.QGIS_VERSION_INT >= 10900:
            rb = self.rubberBand
            rb.reset(QGis.Point)
            rb.addPoint(point)
        else:
            self.vMarker = QgsVertexMarker(self.canvas)
            self.vMarker.setIconSize(10)
            self.vMarker.setCenter(point)
            self.vMarker.show()

        # wait .5 seconds to simulate a flashing effect
        QTimer.singleShot(500,self.resetRubberbands)

    def resetRubberbands(self):
        print "resetting rubberbands.."
        canvas = self.canvas
        if QGis.QGIS_VERSION_INT >= 10900:
            self.rubberBand.reset()
        else:
            self.vMarker.hide()
            canvas.scene().removeItem(self.vMarker)
        self.crossRb.reset()
        print "completed resetting.."