AO开发中的一些小技巧(A)

<P>开发中的一些小技巧:
1.
/////////
  根据feature 的oid 取得对应的feature
  Set pfeature = pFeatureClass.GetFeature(CStr(sOid))
////////</P>
<P>  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</P>
<P>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
  ...</P>
<P>  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?
</P>

<img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em04.gif" /><img src="images/post/smile/dvbbs/em04.gif" /><img src="images/post/smile/dvbbs/em05.gif" /><img src="images/post/smile/dvbbs/em05.gif" />

<img src="images/post/smile/dvbbs/em01.gif" />

感谢他，我就是受益者！

等着出b，c，d<img src="images/post/smile/dvbbs/em04.gif" />

<img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em02.gif" />

好! <img src="images/post/smile/dvbbs/em07.gif" />

支持！