[processing] show warning when file-based layer could not be loaded and dependent params updated

volaya · nyalldawson · commit 722e4fe30879 · 2019-01-30T02:35:24.000+11:00
For algorithms with multiple parameters depending on a vector layer parameter, the code that loads the layer in the background is called repeatedly, impacting performance. A small layer cache is implemented with these changes, so the dialog only tries to load the layer once. (cherry picked from commit 6eaa511)
diff --git a/python/plugins/processing/gui/wrappers.py b/python/plugins/processing/gui/wrappers.py
@@ -45,6 +45,7 @@
     QgsSettings,
     QgsProject,
     QgsMapLayer,
+    QgsVectorLayer,
     QgsProcessing,
     QgsProcessingUtils,
     QgsProcessingParameterDefinition,
@@ -78,7 +79,8 @@
     QgsProcessingModelChildParameterSource,
     QgsProcessingModelAlgorithm,
     QgsRasterDataProvider,
-    NULL)
+    NULL,
+    Qgis)
 
 from qgis.PyQt.QtWidgets import (
     QCheckBox,
@@ -1049,6 +1051,7 @@ class FeatureSourceWidgetWrapper(WidgetWrapper):
     NOT_SELECTED = '[Not selected]'
 
     def createWidget(self):
+        self.fileBasedLayers = {}
         if self.dialogType == DIALOG_STANDARD:
             widget = QWidget()
             layout = QHBoxLayout()
@@ -1391,6 +1394,7 @@ class VectorLayerWidgetWrapper(WidgetWrapper):
     NOT_SELECTED = '[Not selected]'
 
     def createWidget(self):
+        self.fileBasedLayers = {}
         if self.dialogType == DIALOG_STANDARD:
             widget = QWidget()
             layout = QHBoxLayout()
@@ -1576,14 +1580,26 @@ def postInitialize(self, wrappers):
                 break
 
     def parentValueChanged(self, wrapper):
-        self.setLayer(wrapper.parameterValue())
+        value = wrapper.parameterValue()
+        if value in wrapper.fileBasedLayers:
+            self.setLayer(wrapper.fileBasedLayers[value])
+        else:
+            self.setLayer(value)
+            wrapper.fileBasedLayers[value] = self._layer
 
     def setLayer(self, layer):
         if isinstance(layer, QgsProcessingFeatureSourceDefinition):
             layer, ok = layer.source.valueAsString(self.context.expressionContext())
         if isinstance(layer, str):
             layer = QgsProcessingUtils.mapLayerFromString(layer, self.context)
+            if not isinstance(layer, QgsVectorLayer) or not layer.isValid():
+                self.dialog.messageBar().clearWidgets()
+                self.dialog.messageBar().pushMessage("", self.tr("Could not load selected layer/table. Dependent field could not be populated"),
+                                                     level=Qgis.Warning, duration=5)
+                return
+
         self._layer = layer
+
         self.refreshItems()
 
     def refreshItems(self):
