18. 使用插件层

提示

如果您在pyqgis控制台之外，则此页面上的代码片段需要以下导入：

from qgis.core import (
    QgsPluginLayer,
    QgsPluginLayerType,
    QgsMapLayerRenderer,
    QgsApplication,
    QgsProject,
)

from qgis.PyQt.QtGui import QImage

如果您的插件使用其自己的方法来渲染地图图层，则基于 QgsPluginLayer 可能是实现这一点的最好方式。

18.1. 将QgsPluginLayer子类化

下面是一个最小的QgsPluginLayer实现示例。它是基于 Watermark example plugin 。

自定义呈现器是工具的一部分，用于定义画布上的实际绘图。

class WatermarkLayerRenderer(QgsMapLayerRenderer):

    def __init__(self, layerId, rendererContext):
        super().__init__(layerId, rendererContext)

    def render(self):
        image = QImage("/usr/share/icons/hicolor/128x128/apps/qgis.png")
        painter = self.renderContext().painter()
        painter.save()
        painter.drawImage(10, 10, image)
        painter.restore()
        return True

class WatermarkPluginLayer(QgsPluginLayer):

    LAYER_TYPE="watermark"

    def __init__(self):
        super().__init__(WatermarkPluginLayer.LAYER_TYPE, "Watermark plugin layer")
        self.setValid(True)

    def createMapRenderer(self, rendererContext):
        return WatermarkLayerRenderer(self.id(), rendererContext)

    def setTransformContext(self, ct):
        pass

    # Methods for reading and writing specific information to the project file can
    # also be added:

    def readXml(self, node, context):
        pass

    def writeXml(self, node, doc, context):
        pass

插件层可以作为任何其他地图层添加到项目和画布：

plugin_layer = WatermarkPluginLayer()
QgsProject.instance().addMapLayer(plugin_layer)

加载包含这样一个层的项目时，需要一个工厂类：

class WatermarkPluginLayerType(QgsPluginLayerType):

    def __init__(self):
        super().__init__(WatermarkPluginLayer.LAYER_TYPE)

    def createLayer(self):
        return WatermarkPluginLayer()

    # You can also add GUI code for displaying custom information
    # in the layer properties
    def showLayerProperties(self, layer):
        pass


# Keep a reference to the instance in Python so it won't
# be garbage collected
plt =  WatermarkPluginLayerType()

assert QgsApplication.pluginLayerRegistry().addPluginLayerType(plt)