pyqgis - How can I trigger a QGIS plugin Event from map refresh?

I have a combobox in my plugin (python Qt dockable widget) that needs to contain the currently open rasters.

How do I trigger an update of the plugin when something new gets added to the map?

Answer

There's a couple of methods which I use (note that it may not be the most efficient solution):

• 
  

  (using Combo Box) - Add the following line before you populate your combo box:

  
  

  self.dockwidget.comboBox.clear()
  

  
  

  Then when you add a new layer, close your plugin and open it again, the combo box should be re-populated with the new additions.

  
  

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• 
  

  (using QgsMapLayerComboBox) - This is automatically updated when any changes are made to the layer list (i.e. layers added/removed, names changed etc) without you having to refresh the plugin. I would recommend this method. You can set it so that it only recognises raster layers by using something like:

  
  

  self.dockwidget.mapLayerComboBox.setFilters( QgsMapLayerProxyModel.RasterLayer )
  

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Note: When using QGIS custom widgets, you may need to edit your dockwidget_base.ui file, find the QgsMapLayerComboBox class (usually at the end of the file) and replace the

to qgis.gui.h.