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I created the simple frame .UI file, compiled with pyuic4, and tried the to load the shapefile "world_borders.shp". However, the map doesn't display at the first time. I have to click out the window to make it appear. After everything works! I am working in Windows 7. Instalation "osgeo4w-setup-x86". Qgis 2.2.0-Valmiera

Why does QgsMapCanvas in Qgis 2.2.0-Valmiera only appear after losing focus?

Here is my code:

class ShapeViewer(QMainWindow, Ui_MainWindow):
    def __init__(self):
        self.canvas = QgsMapCanvas()
        self.layout = QVBoxLayout(self.frame)
        file = QFileDialog.getOpenFileName(self,"Open", ".", "Shp(*.shp)")
        layer = QgsVectorLayer(file, "My Shape", "ogr")
        cl = QgsMapCanvasLayer(layer)

def main(argv):
    # create Qt application
    app = QApplication(argv)

    # Initialize qgis libraries
    QgsApplication.setPrefixPath(qgis_prefix, True)
    # create main window
    wnd = ShapeViewer()
    # run!
    retval = app.exec_()

    # exit
if __name__ == "__main__":
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This is interesting I am seeing this in a custom QGIS app I made too against 2.2. Not sure why yet. –  Nathan W Feb 26 '14 at 21:33
@NathanW it's only happend in a custom QGIS app. I fixed this error by switching to version 2.0.1. I think it's a bug from 2.2. I'm not sure, because I have no experience in qgis. –  Marcelo Pacheco Apr 10 '14 at 22:03
Yes it's a bug. There is a workaround. –  Nathan W Apr 11 '14 at 3:21

4 Answers 4

This is a bug in 2.2 with the canvas and it's redraw event. The redraw event is called when the widget is first shown and it kicks off a timer which stops the canvas from painting.

The workaround is as simple as calling:


The first time the widget is shown.

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I had the same issue. I solve it by calling to after configuring the qgsmapcanvas. Hope it helps.

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Barna, thx for your answer, but I did what you wrote but it doesn't work. –  Marcelo Pacheco Apr 2 '14 at 15:14
up vote 0 down vote accepted

I fixed this error by switching to version 2.0.1 I think it's a bug from 2.2. I'm not sure, because I have no experience in qgis.

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This bug cost me a day. The workaround is very specific. You must freeze and unfreeze the canvas at just the right time while also refreshing and repainting the canvas:

# Freeze the Canvas
# to make it immune to
# buggy events
# Show the frozen canvas
# Refresh the canvas content
# Now, and only now, we can unfreeze
# the canvas
# And finally, we can safely repaint it.
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