第5章數(shù)據(jù)查詢與功能實現(xiàn)

在MapObjects如何查詢各類幾何對象（點，線段， SearchShape(shape,sear expression)幾何圖形對象在空間關(guān)系上符合參數(shù)searethod所表達(dá)式expression是一個滿足SQL要省略表達(dá)式,則使用一個空字符串SetobjRecset=Objma yer.SearchShape(shape, ethod,expression)objRecset: yer：用戶定義的一個矢量圖層對象 Expression：一個構(gòu)成SQL語句的'where'從句部分的字符串。應(yīng)當(dāng)注意MapObjects遵遁ANSISQL標(biāo)準(zhǔn)而不是JetDatabaseEngineSQL moPointInPolygon：使用此參數(shù) 圖層，shape是一個點對象；判接觸完全或部分地處在要查找的幾何對象中完全或部分地包myPolylaer.SearchShape(myPolylaer.SearchShape(pt1,moPointInPolygon,“”方法：SearchByDistanceshapetolerance,shpe為中心tolerance你要省略表達(dá)式,(“”),這對于Shape文件、ARC/INFO圖層數(shù)據(jù)，Shape(youcannotpassaRecordsetderivedfromanSDElayer).SetobjRecset=shape,tolerance,expression) PrivateConstSEARCHTOLPIXELS3（為3個像素theTol=Map1.ToMapDistance(SEARCHTOLPIXELS*Screen.TwipsPerPixelX)（將地圖控件上3個像素所表一個與屏幕無關(guān)的單位，用來保證屏幕應(yīng)用程序?qū)ζ?Twip=1/20Point=1/1440Inch=1/567cm（打印時的一英DimfoundShapeAsDimsymAsNewPrivateConstSEARCHTOLPIXELS=DimbufClickAsPublicrecsAsPrivateSubMap1_MouseDown(ButtonAsInteger,ShiftAsInteger,xAsSingle,yAsIfMap1.Layers.Count=0ThenExitIfOption1.Value=TrueAnd"ExitEndIfCheck1.Value=TrueFindFeaturex,PublicSubFindFeature(ByValxAsDouble,ByValyAsDouble)IfOption1.Value=TrueDimptAsNewSetpt=Map1.ToMapPoint(x,FindPolygonElseIfOption2.Value=TrueCallFindClosest(x,ElseIfOption3.Value=TrueCallFindLineOrPoint(x,EndForm2.ZOrderEndPublicSubFindPolygon(ptAsDimshpAsSetrecs=Map1.Layers(0).SearchShape(pt,moPointInPolygon,"")Ifrecs.Count=0ThenExitSetshp=SetfoundShape=EndSubPublicSubFindClosest(ByValxAsDouble,ByValyAsDouble)DimminDistAsDimthisDistAsDimmapPtAsDimsubrecsAsDimshpAsDimstrFIDAsSetmapPt=Map1.ToMapPoint(x,Setrecs=minDist=strFID=DoWhileNotSetshp=thisDist=IfthisDist<minDistminDist=strFID=EndSetsubrecs="&strFID)Setrecs=SetfoundShape=EndSubPublicSubFindLineOrPoint(ByValxAsDouble,ByValyAsDouble)DimshpAsDimptAsNewDimtheTolAstheTol=ELS*Screen.TwipsPerPixelX)Label3.Caption="tolerence:"&theTol&vbCrLf&"TPPX:"&Setpt=Map1.ToMapPoint(x,Setrecs=theTol,"")Ifrecs.Count=0ThenExitSetshp=SetfoundShape=SetbufClick=pt.Buffer(theTol,EndSub 方法：AddRelate object.AddRelate(toField,sourceTable,fromField,[checkFieldsasBoolean])object：一個 yer對toField：與Ma sourceTable要與Ma checkFields(可選參數(shù))：一個 AddRelate在一個Ma yer和一個數(shù)據(jù)表間建立關(guān)聯(lián)。 中屬性字段。如果在外部數(shù)據(jù)表中找到與fromField與你應(yīng)確保由sourceTable指定的外部數(shù)據(jù)表中的字段名稱 在使用AddRelate方法時，將對外部數(shù)據(jù)表支持關(guān)聯(lián)的字段類型是：數(shù)值型字符/字符串字段型。如果toFieldfromField其中的任何一False,關(guān)聯(lián)也不會成功。參數(shù)checkFields的缺省值是真True。當(dāng)參數(shù)checkFields為真True時,AddRelate方法對外部數(shù)字段fromField是不是外部數(shù)據(jù)表sourceTable如果不是,是否在fromField字段上建立了索引？(MapObjects不會使用fromField的索引,只是查看如果以上的任一個條件為真那么AddRelate將成功 ADO2.5對象OptionDimpTableAsNewMapObjects2.TableDimpLyrAs PrivateSubDimrecsAsNewSetrecs=CallEndSubConnectToShapefile(databaseStrAsString,lyrNameAsString)DimdcAsNew DimgdsAsSetpLyr=New dc.Database=Setgds=SetpLyr.GeoDataset=Map1.Layers.AddEndSubPublicSubResetListBox()DimrecsAs'ResettheRecordsetSetrecs='Clearthefield'RebuildthefieldDimtdescAsSettdesc=DimiAsFori=0Totdesc.FieldCount- Iftdesc.FieldName(i)<>"Shape"Andtdesc.FieldName(i)<>"FeatureId"ThenlstFields.AddItemEndNextEndSubADOcommandconnectionpDimconnStrAsStringDimSQLStrAsconnStr="Provider= Source&App.Path&科考旅游ACCESS.mdb;"SQLStr“Select*from科考旅游資源點DimlyrFldNameAsStringDimtblFldNameAslyrFldName“OBJECTID”'通過ADO(SQL語句IfConnectToTable(connStr,SQLStr)DimboolRelateAs boolRelate=pLyr.AddRelate(lyrFldName,pTable,IfboolRelateMsgBox返回的記錄數(shù)pLyr.Records.ExportApp.Path&CallResetListBoxEndEndEndFunctionConnectToTable(connStrAsString,SQLStrAsString)AsBooleanOLEDB驅(qū)動及ADO建立到外部數(shù)據(jù)表的DimpConnAsNewDimpCommandAs pConn.ConnectionString=pConn.ModeadModeReadpConn.Open'打開聯(lián)接mandType=mandText=SetpTable=New mand=DimrecsAsSetrecs=IfrecsIsNothingConnectToTable=ConnectToTable=EndEndFunctionPrivateSubMsgB