AO开发中的一些小技巧

百花草

1.
/////////
根据feature 的oid 取得对应的feature
Set pfeature = pFeatureClass.GetFeature(CStr(sOid))
////////

Set pfeature = pFeatureClass.GetFeature(lOid)
当不存在featureOID 为 lOid 时，会出错，改为通过函数处理，为了减少时间，也不采用featureclass.search等方法。
这样成功就取得对应的feature,不然就返回nothing,虽然函数中会产生错误，但不会影响正常操作。
Private Function get_FeatureByOid(pFcls As IFeatureClass, lOid As Long) As IFeature
On Error GoTo EH
Set get_FeatureByOid = Nothing
Dim pfeature As IFeature
If pFcls Is Nothing Then Exit Function
If lOid < 0 Then Exit Function

If pFcls.HasOID Then
Set pfeature = pFcls.GetFeature(lOid)
Set get_FeatureByOid = pfeature
End If
EH:
'
End Function

2.取得指定字段名的值
/////////
NameString = pfeature.Value(pFeatureClass.FindField("XXXXXX"))
/////////
同样道理，当找不到字段名为 XXXXXX 的字段时，pfeatureclass.findfield("XXXXXX") 返回值为-1
那么 pfeature.value(-1)当然会出错
同样通过函数替换
Public Function Get_FClsFldIdx(ByVal pFeatureCls As IFeatureClass, ByVal sFldName As String) As Long
'if success then return a value bigger than -1,if not found,then return -1
On Error GoTo EH
Get_FClsFldIdx = pFeatureCls.FindField(sFldName)

Exit Function
EH:
'
End Function
使用时:
...
lFldIdx = m_MyLib.Get_FClsFldIdx(pFeatureClass, "XXXXXX")
If lFldIdx = -1 Then Exit Function '不存在名称为"XXXXXX"的字段
...
Dim pfeature As IFeature
Dim NameString As String

For i = 0 To pFeatureClass.FeatureCount(Nothing) - 1
Set pfeature = get_FeatureByOid(pFeatureClass, CLng(i))
If Not pfeature Is Nothing Then
NameString = pfeature.Value(lFldIdx)
....
End If
Next i
...

以上两例是比较简单的例子，在ao在线帮助中也经常有一些会产生错误的隐患，AO只是示例用法，但用法是否合理，要在自已的开发实践中总结。
这样，使用AO中提供的代码，有的人能调试通过，运行得很正常，则其他人有可能调试不通过。
希望能对初学者有帮助

wwxx

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359732265

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