from PyQt4 import QtCore, QtGui
from qgis import core, gui, utils
from qgis.gui import QgsMapCanvasLayer

mc = iface.mapCanvas()
layers = mc.mapRenderer().layerSet()
if not layers:
    self.ui.displayFileNameTextEdit.setText("No layer to display.")
else:
    for layer in layers: #layer is one id
        self.ui.qgsMapCanvas.setExtent(layer.extent())
        self.ui.qgsMapCanvas.setLayerSet( [ QgsMapCanvasLayer(layer) ] )
        self.ui.qgsMapCanvas.refresh()

from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import QFile, QFileInfo
from qgis import core, gui, utils
from qgis.core import QgsRasterLayer
from qgis.gui import QgsMapCanvasLayer
from qgis.utils import iface

layers = iface.legendInterface().layers()
for each_layer in layers:
    fileName = each_layer
    fileInfo = QFileInfo(fileName)
    baseName = fileInfo.baseName()
    self.layer = QgsRasterLayer(fileName, baseName)

    QgsMapLayerRegistry.instance().addMapLayer(self.layer)
    self.canvas = self.ui.qgsMapCanvas
    self.canvas.setCanvasColor(QtCore.Qt.white)
    self.canvas.setExtent(self.layer.extent())
    self.canvas.setLayerSet( [ QgsMapCanvasLayer(self.layer) ] )
    r = QgsRubberBand(self.ui.qgsMapCanvas, True)
    self.canvas.setCurrentLayer(self.layer)
    self.canvas.setVisible(True)
    self.canvas.refresh()

legend = self.iface.legendInterface()
layers = legend.layers()
for each_layer in layers:
    if each_layer.type() == "RasterLayer":
        print each_layer.id()
        print each_layer.name()