Feature request #2392

Plugin layer registry

Added by Mathias Walker over 13 years ago. Updated over 13 years ago.

Assignee:Martin Dobias
Category:Python plugins
Pull Request or Patch supplied: Resolution:fixed
Easy fix?:No Copied to github as #:12452


This patch adds a plugin layer registry to support plugin specific maplayers.

Plugins can register a function that creates the specific subclass of QgsMapLayer. This allows to instantiate the corresponding plugin layer when reading the project file.


see sample plugin for details

  • create subclass of QgsMapLayer
    • implement isEditable(), draw() and writeXml()
  • create subclass of QgsPluginLayerCreator
    • implement createLayer() e.g. as callback to a plugin function
  • init plugin
    • register PluginLayerCreator using QgsPluginLayerRegistry.instance().addCreator()
  • add layer
    • create PluginMapLayer instance of layer type QgsMapLayer.PluginLayer
    • add layer using QgsMapLayerRegistry.instance().addMapLayer()
  • save project
    • calls PluginMapLayer.writeXml()
    • save plugin id string as attribute "type"
  • load project
    • QgsPluginLayerRegistry calls createLayer() for all registered QgsPluginLayerCreators
    • plugin creates and adds a new PluginMapLayer instance if the attribute "type" matches their id string
  • unload plugin
    • unregister PluginLayerCreator using QgsPluginLayerRegistry.instance().removeCreator()

enh2392_plugin_layer_registry.diff Magnifier - Plugin layer registry patch (10.6 KB) Mathias Walker, 2010-01-25 07:29 AM

enh2392_sample_layer_plugin.tar.gz - Sample layer plugin (5.26 KB) Mathias Walker, 2010-01-25 07:31 AM

sample_layer_plugin_updated.tar.gz - plugin compatible with implementation in trunk (7.15 KB) Martin Dobias, 2010-01-26 08:15 AM


#1 Updated by luca76 - over 13 years ago


very interesting patch!

#2 Updated by Marco Hugentobler over 13 years ago

Martin, do you have time to review this patch?

#3 Updated by Giovanni Manghi over 13 years ago

  • Resolution set to fixed
  • Status changed from Open to Closed

applied in 8f32f25a (SVN r12835)

#4 Updated by Martin Dobias over 13 years ago

Applied in 8f32f25a (SVN r12835) with several modifications:

  • plugin layers are subclassed from QgsPluginLayer and not directly from QgsMapLayer for convenience
  • each plugin layer type has its unique name used in QgsPluginLayerRegistry - instead of dynamically assigned IDs
  • layer creator has been enhanced to return the unique layer type name and to be able to open layer's properties dialog (and renamed to QgsPluginLayerType as it's not just a creator)
  • simplified creation of plugin layers: for the unique type name the registry returns instance of the layer
  • when the plugin layer type is removed from registry, layer of that type are removed automatically

I've modified also the sample plugin to reflect my changes.

Sample plugin from the example:

LAYER_TYPE = "sample" 

class [[SamplePluginLayer]](QgsPluginLayer):
  def +init+(self, width=None):
    [[QgsPluginLayer]].+init+(self, LAYER_TYPE, "Sample plugin layer")

    self.width = width if width is not None else 256

  def draw(self, rendererContext):
    painter = rendererContext.painter()
    painter.drawRect(32, 32, self.width, 128)
    return True

  def readXml(self, node):
    self.width = node.toElement().attribute("width", "256").toInt()r0
    return True

  def writeXml(self, node, doc):
    element = node.toElement()
    # write plugin layer type to project (essential to be read from project)
    element.setAttribute("type", "plugin")
    element.setAttribute("name", LAYER_TYPE)
    # custom properties
    element.setAttribute("width", str(self.width))
    return True

Definition of the layer's type with auxiliary methods:

class [[SamplePluginLayerType]](QgsPluginLayerType):
  def +init+(self):
    [[QgsPluginLayerType]].+init+(self, LAYER_TYPE)

  def createLayer(self):
    return [[SamplePluginLayer]]()

  def showLayerProperties(self, layer):
    res = QInputDialog.getInt(None, "Sample plugin", "Set width of the rectangle", layer.width, 1, 1000)
    if resr1: # dialog was not cancelled
      layer.width = resr0
      # trigger repaint

    # indicate that we have shown the properties dialog
    return True


    [[QgsPluginLayerRegistry]].instance().addPluginLayerType( [[SamplePluginLayerType]]() )

Creation of the layer:

layer = [[SamplePluginLayer]]()
# -or-



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