canvas = QgsMapCanvas()
self.setCentralWidget(canvas)

canvas.setCanvasColor(Qt.white)
canvas.enableAntiAliasing(True)

file = QFileDialog.getOpenFileName(self,'Open Shapefile', '.', 'Shapefiles (*.shp)')
fileInfo = QFileInfo(file)

print fileInfo.fileName()

layer = QgsVectorLayer(file, fileInfo.fileName(), 'ogr')
if not layer.isValid():
      raise IOError, "Failed to open the layer"

# add layer to the registry
QgsMapLayerRegistry.instance().addMapLayer(layer)

# set extent to the extent of our layer
canvas.setExtent(layer.extent())

# set the map canvas layer set
canvas.setLayerSet( [ QgsMapCanvasLayer(layer) ] )