计算机科学与技术：VB.NET应用教程 978-7-302-09622-1 Advanced VB.NET Chapter 6

《计算机科学与技术：VB.NET应用教程 978-7-302-09622-1 Advanced VB.NET Chapter 6》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、Chapter6TheBinaryAccessMethodObjectivesTheBinaryAccessMethodEncryptionSerializationTheDirectAccessMethodLab6:TheBinaryAccessMethodSuggestedHomeAssignments2Copyright2004PearsonEducation,Inc.TheBinaryAccessMethodReadsandwritesthedatainafileasbytesthatcanbeaccessedatanyoffset(positioninthefile)

2、andatanylength.Enablesencryptionandcompressionbyvirtueofallowingtheprogramtoaccessthedataonebyteatatimeandinanysequence.Providesamethodformakingobjectspersistent.Allowscreatingandhandlingsingleuserrecordsasthoughthroughadatabasebutwithoutresortingtoactuallyimplementingone.3Copyright2004Pears

3、onEducation,Inc.BinaryAccessClassesTheFileStreamclass.TypicalsequenceofcodeOpenthefileasaFileStreamobject,Readand/orwritedatathroughthemethodsoftheFileStreamobject,ReleasetheconnectionoftheobjecttothefilewiththeClosemethod.Whatcanbedonewiththefiledependsontheconstructorparameters.4Copyright2

4、004PearsonEducation,Inc.FileStreamParametersFileStreamconstructorparametersFilepathFileModeFileAccessLockMechanismDimmyStream2AsIO.FileStreammyStream2=NewIO.FileStream(txtMyFile.Text,_IO.FileMode.Open,_IO.FileAccess.ReadWrite,_IO.FileShare.Read)5Copyright2004PearsonEducation,Inc.FileModeValu

5、es(1)IO.FileMode.AppendOpensanexistingfileandappendsthenewdatatoitsend.Ifthefiledoesnotexist,itwillbecreated.IO.FileMode.CreateCreatesanewfile.Ifthefileexists,itisoverwritten.IO.FileMode.CreateNewCreatesanewfile.Butifthefilealreadyexists,anIOExceptionexceptionisthrown.IO.FileMode.OpenOpensan

6、existingfile.Ifthefiledoesnotexist,anIOExceptionexceptionisthrown.6Copyright2004PearsonEducation,Inc.FileModeValues(2)IO.FileMode.OpenOrCreateOpensanexistingfile.Ifthefiledoesnotexist,itiscreated.IO.FileMode.TruncateOpensanexistingfilebutdeletesitsdata.7Copyright2004PearsonEducation,Inc.File

7、AccessValuesIO.FileAccess.ReadAllowsonlyreadingthedata.IO.FileAccess.ReadWriteAllowsreadingandwritingdata(default).IO.FileAccess.WriteAllowsonlywritingdata.8Copyright2004PearsonEducation,Inc.LockingValuesIO.FileShare.NonePlacesalockonthefile.Noothe