Measure Point Along a Line

Question

Looking to find Distance along a line(road) by a user input(Mouse Click). Here is my python code TESTED and works

def onMouseDownMap(self, x, y, button, shift):
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd)[0]
pointGeom = arcpy.PointGeometry(arcpy.Point(x, y), mxd.activeDataFrame.spatialReference)
road_layer = arcpy.mapping.ListLayers(mxd, "narr", df)[0]
arcpy.SelectLayerByLocation_management(road_layer, "WITHIN_A_DISTANCE", pointGeom, "50 FEET")
arcpy.RefreshActiveView()
output_layer = arcpy.CopyFeatures_management(road_layer, arcpy.Geometry())
dist_along_road = output_layer[0].measureOnLine(pointGeom)
pythonaddins.MessageBox(dist_along_road / 5280, "Address", 1)

Answer 1

First of all does your output_layer actually contain any geometries? I ask this as your select by location is set to INTERSECT. No one can ever click on a line, so may be change that to closest or create a buffer around your point and use that as the selecting geometry.

Secondly measureOnLine is a method for Polyline geometry, your code is trying to run that on your cursor cursorRoad, you need to get the row from the cursor then the geometry. Suggest you read this page and study the code.