在使用arcmap工具箱里的工具的时候，如果已经加载相应的图层或者数据，就可以使用下拉列表的方式进行选择，也就是说工具会自动加载这些图层只需要选择即可。这一节就说下如何自动化的选择图层和数据。
1、 设置参数类型为相应的Featurelayer、RasterLayer等带Layer的参数
看一个实例代码：
import arcpy
#获取图层
fc = arcpy.GetParameter(0)
arcpy.RepairGeometry_management(fc)
按照教程三创建arcpy工具，设置参数时候如下进行设置：
就可以实现图层的自动选择，如下图：
2、 通过代码自动获得图层或者数据
看一个实例代码：
import arcpy, os
#Read parameters from dialog
mxdPath = arcpy.GetParameterAsText(0)
dfName = arcpy.GetParameterAsText(1)
layerName = arcpy.GetParameterAsText(2)
layerFile = arcpy.GetParameterAsText(3)
outMXD = arcpy.GetParameterAsText(4)
#Update layer symbology
mxd = arcpy.mapping.MapDocument(mxdPath)
df = arcpy.mapping.ListDataFrames(mxd,dfName)[0]
updateLayer = arcpy.mapping.ListLayers(mxd,layerName)[0]
sourceLayer =arcpy.mapping.Layer(layerFile)
arcpy.mapping.UpdateLayer(df, updateLayer,sourceLayer, True)
#Save changes to new MXD and automaticallyopen
mxd.saveACopy(outMXD)
os.startfile(outMXD)
del mxd, sourceLayer
其工具参数如下设置：
参数设置后面有个Validation
通过下面的Edit按钮可以对里面的代码进行编辑，编辑之后，点击保存，并点击下面的应用按钮即可。粘贴代码如下：
class ToolValidator:
"""Class for validating a tool's parameter values andcontrolling
thebehavior of the tool's dialog."""
def__init__(self):
"""Setup the Geoprocessor and the list of toolparameters."""
import arcpy
self.params = arcpy.GetParameterInfo()
definitializeParameters(self):
"""Refine the properties of a tool's parameters. This method is
called when the tool is opened."""
return
defupdateParameters(self):
"""Modify the values and properties of parameters beforeinternal
validation is performed. Thismethod is called whenever a parmater
has been changed."""
import arcpy
#Update Data Frames list
if self.params[0].value:
mxd = arcpy.mapping.MapDocument(self.params[0].value.value)
dataFrames = arcpy.mapping.ListDataFrames(mxd)
dfList = []
for df in dataFrames:
dfList.append(df.name)
dfList.sort()
if not self.params[1].altered:
self.params[1].filter.list = dfList
#Update Layer list (in selected data frame)
if self.params[1].value:
df = arcpy.mapping.ListDataFrames(mxd, (self.params[1].value))[0]
lyrs = arcpy.mapping.ListLayers(mxd, "", df)
layerList = []
for lyr in lyrs:
layerList.append(lyr.name)
layerList.sort()
if not self.params[2].altered:
self.params[2].filter.list = layerList
return
defupdateMessages(self):
"""Modify the messages created by internal validation foreach tool
parameter. This method is calledafter internal validation."""
return