嗨... 我有一个方法的以下两个摘录。它基本上从DataReader读取数据 并且 将其加载到集合中。 摘录A： * ******* 使用ProjectData 而.Read Me.Add（DirectCast（.Item（" project_id"）） ，Guid），_ DirectCast（.Item（" start_date"），DateTime），_ DirectCast（.Item（" end_date"），DateTime）， _ DirectCast（.Item（" priority"），Integer），_ DirectCast（.Item（" description"），String），_ DirectCast（.Item（" project_manager"），String） 结束时 结束 摘录B： ******** 使用ProjectData 而.Read Me.Add（.Item（" project_id"）， .Item（" start_date"）， .Item（" end_date"）， .Item（" priority"）， .Item（" description"）， .Item（" project_manager"） E. nd While 结束 问题： 自动投射是否优于显式投射？当我运行ILDASM时，我发现 在每个DirectCast上都有拆箱但是在摘录B中，没有任何任何。 以下摘录A和B的ILDASM片段： ILDASM（摘录A） * *************** IL_0098：ldloc.2 IL_0099：ldstr" description" IL_009e：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_00a3：unbox [mscorlib] System.Int32 IL_00a8：ldobj [mscorlib] System.Int32 ILDASM（摘录B） **************** IL_0092：ldloc.2 IL_0093：ldstr" description" IL_0098：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_009d：call int32 [Microsoft.VisualBasic] Microsoft.VisualBasic.CompilerServices.IntegerType :: F romObject （对象） 任何指针文章解释了引擎盖下发生的事情。与 关于 铸造也将非常受欢迎。 干杯！
解决方案这是最好的猜测...但我也想学习这个... 我会假设直接投射会更快（主要是因为我知道直接 施法更快）而且这个调用 [Microsoft.VisualBasic] Microsoft.VisualBasic.CompilerServices。 IntegerType :: F romObject（object） 我认为FromObject是一个类并在堆上创建。我会 也假设该方法中有更多的代码需要更长的时间来执行。虽然unbox（我不知道这意味着什么）似乎很可靠。 非常直接。我不知道，只是假设。 我认为从FromObject 方法看到反汇编是100％肯定会有所帮助。 HTH， CJ " tinman" < DW **** @ yahoo>在消息中写道 新闻：呃************** @ TK2MSFTNGP12.phx.gbl ... 嗨... 我有一个方法的以下两个摘录。它基本上从DataReader读取数据并将其加载到集合中。 摘录A： ******** 随着ProjectData 当.Read Me.Add（DirectCast（.Item（" project_id"），Guid），_ DirectCast（.Item（" start_date"），DateTime），_ DirectCast（.Item（" end_date"），DateTime），_ DirectCast（.Item（" priority"），Integer），_ DirectCast（.Item（" description"） ;），String），_ DirectCast（.Item（" project_manager"），String）结束时 摘录B ： ******** 使用ProjectData 而.Read Me.Add（.Item（" project_id"），。Item（ start_date），。Item（" end_date"）， .Item（" priority"），。Item（" description"），。Item（" project_manager"）结束时结束 问题： 自动投射是否优于显式投射？当我运行ILDASM时，我发现在每个DirectCast上都有拆箱但是在摘录B中，没有任何内容。 以下摘录A和B的ILDASM： ILDASM（摘录A） **************** IL_0098：ldloc.2 IL_0099：ldstr" description" IL_009e：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_00a3：unbox [mscorlib] System.Int32 IL_00a8：ldobj [mscorlib] System.Int32 ILDASM（摘录B） **************** IL_0092： ldloc.2 IL_0093：ldstr" description" IL_0098：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_009d：调用int32 [Microsoft.VisualBasic] Microsoft.VisualBasic.CompilerServices.IntegerType :: F romObject（object） 指向文章的任何指针都可以解释引擎盖下的内容。 关于铸造也将非常感激。 干杯！
Tinman， 除了William和我给出的早期答案之外，第一个是更正确的，但是我会在第一次回复时使用我给出的技术 而不是DirectCast。 使用Option Strict On，需要第一个，更正确，其中 你说的是project_id是一个GUID，开始日期是一个DateTime ...你 不允许编译器为你做出决定... 另外使用Option Strict On允许你在编译时间而不是运行时捕获一些错误。 希望这有助于 Jay " tinman" < DW **** @ yahoo>在消息中写道 新闻：呃************** @ TK2MSFTNGP12.phx.gbl ...
嗨... 我有一个方法的以下两个摘录。它基本上从DataReader读取数据并将其加载到集合中。 摘录A： ******** 随着ProjectData 当.Read Me.Add（DirectCast（.Item（" project_id"），Guid），_ DirectCast（.Item（" start_date"），DateTime），_ DirectCast（.Item（" end_date"），DateTime），_ DirectCast（.Item（" priority"），Integer），_ DirectCast（.Item（" description"） ;），String），_ DirectCast（.Item（" project_manager"），String）结束时 摘录B ： ******** 使用ProjectData 而.Read Me.Add（.Item（" project_id"），。Item（ start_date），。Item（" end_date"）， .Item（" priority"），。Item（" description"），。Item（" project_manager"）结束时结束 问题： 自动投射是否优于显式投射？当我运行ILDASM时，我发现在每个DirectCast上都有拆箱但是在摘录B中，没有任何内容。 以下摘录A和B的ILDASM： ILDASM（摘录A） **************** IL_0098：ldloc.2 IL_0099：ldstr" description" IL_009e：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_00a3：unbox [mscorlib] System.Int32 IL_00a8：ldobj [mscorlib] System.Int32 ILDASM（摘录B） **************** IL_0092： ldloc.2 IL_0093：ldstr" description" IL_0098：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_009d：调用int32 [Microsoft.VisualBasic] Microsoft.VisualBasic.CompilerServices.IntegerType :: F romObject（object） 指向文章的任何指针都可以解释引擎盖下的内容。 关于铸造也将非常感激。 干杯！
谢谢你们.... 我相信Get * Type *比DirectCast方法效果更好。结果 IL显得更精简... 在使用DirectCast的最初IL中，我担心所有拆箱都会导致性能问题因为它会继续读取循环中的数据（而。读取） .. ...... 干杯...... " tinman" < DW **** @ yahoo>在消息中写道 新闻：呃************** @ TK2MSFTNGP12.phx.gbl ...
嗨... 我有一个方法的以下两个摘录。它基本上从DataReader读取数据并将其加载到集合中。 摘录A： ******** 随着ProjectData 当.Read Me.Add（DirectCast（.Item（" project_id"），Guid），_ DirectCast（.Item（" start_date"），DateTime），_ DirectCast（.Item（" end_date"），DateTime），_ DirectCast（.Item（" priority"），Integer），_ DirectCast（.Item（" description"） ;），String），_ DirectCast（.Item（" project_manager"），String）结束时 摘录B ： ******** 使用ProjectData 而.Read Me.Add（.Item（" project_id"），。Item（ start_date），。Item（" end_date"）， .Item（" priority"），。Item（" description"），。Item（" project_manager"）结束时结束 问题： 自动投射是否优于显式投射？当我运行ILDASM时，我发现在每个DirectCast上都有拆箱但是在摘录B中，没有任何内容。 以下摘录A和B的ILDASM： ILDASM（摘录A） **************** IL_0098：ldloc.2 IL_0099：ldstr" description" IL_009e：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_00a3：unbox [mscorlib] System.Int32 IL_00a8：ldobj [mscorlib] System.Int32 ILDASM（摘录B） **************** IL_0092： ldloc.2 IL_0093：ldstr" description" IL_0098：callvirt实例对象 XXX.Projects.XDataReader :: get_Item（string） IL_009d：调用int32 [Microsoft.VisualBasic] Microsoft.VisualBasic.CompilerServices.IntegerType :: F romObject（object） 指向文章的任何指针都可以解释引擎盖下的内容。 关于铸造也将非常感激。 干杯！
Hi... I have the following two excerpts from a method. It basically reads data from a DataReader and loads it in a collection. Excerpt A: ******** With ProjectData While .Read Me.Add(DirectCast(.Item("project_id"), Guid), _ DirectCast(.Item("start_date"), DateTime), _ DirectCast(.Item("end_date"), DateTime), _ DirectCast(.Item("priority"), Integer), _ DirectCast(.Item("description"), String), _ DirectCast(.Item("project_manager"), String) End While End With Excerpt B: ******** With ProjectData While .Read Me.Add(.Item("project_id"), .Item("start_date"), .Item("end_date"), .Item("priority"), .Item("description"), .Item("project_manager") End While End With Question: Does automatic casting outperform explicit casting ? When I run ILDASM, I find that at each DirectCast, there is unboxing but in Excerpt B, there isn''t any. Snippets of the ILDASM for Excerpt A and B below: ILDASM (Excerpt A) **************** IL_0098: ldloc.2 IL_0099: ldstr "description" IL_009e: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_00a3: unbox [mscorlib]System.Int32 IL_00a8: ldobj [mscorlib]System.Int32 ILDASM (Excerpt B) **************** IL_0092: ldloc.2 IL_0093: ldstr "description" IL_0098: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_009d: call int32 [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.IntegerType ::F romObject(object) Any pointers to articles that explain what goes on "under the hood" with regards to casting would be much appreciated as well. Cheers !
解决方案 This is mearly a guess at best...but I would like to learn this as well... I would assume the direct cast would be faster (mainly because I know direct cast is faster) and also this call [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.IntegerType ::F romObject(object) I would figure that FromObject is a class and created on the heap. I would also assume there is more code inside that method that takes longer to execute. Whereas the unbox (I don''t know what that means necessarily) seems pretty direct. I don''t know, just assuming. I think it would be helpful to see the dissassembly from the FromObject method to be 100% sure. HTH, CJ "tinman" <dw****@yahoo> wrote in message news:uh**************@TK2MSFTNGP12.phx.gbl... Hi... I have the following two excerpts from a method. It basically reads data from a DataReader and loads it in a collection. Excerpt A: ******** With ProjectData While .Read Me.Add(DirectCast(.Item("project_id"), Guid), _ DirectCast(.Item("start_date"), DateTime), _ DirectCast(.Item("end_date"), DateTime), _ DirectCast(.Item("priority"), Integer), _ DirectCast(.Item("description"), String), _ DirectCast(.Item("project_manager"), String) End While End With Excerpt B: ******** With ProjectData While .Read Me.Add(.Item("project_id"), .Item("start_date"), .Item("end_date"), .Item("priority"), .Item("description"), .Item("project_manager") End While End With Question: Does automatic casting outperform explicit casting ? When I run ILDASM, I find that at each DirectCast, there is unboxing but in Excerpt B, there isn''t any. Snippets of the ILDASM for Excerpt A and B below: ILDASM (Excerpt A) **************** IL_0098: ldloc.2 IL_0099: ldstr "description" IL_009e: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_00a3: unbox [mscorlib]System.Int32 IL_00a8: ldobj [mscorlib]System.Int32 ILDASM (Excerpt B) **************** IL_0092: ldloc.2 IL_0093: ldstr "description" IL_0098: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_009d: call int32 [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.IntegerType ::F romObject(object) Any pointers to articles that explain what goes on "under the hood" with regards to casting would be much appreciated as well. Cheers !Tinman, In addition to the earlier answers William and I gave, the first is more correct, although I would use the technique I gave in my first response here instead of DirectCast. Using Option Strict On, which requires the first, is more "correct", in that you are stating that project_id is a GUID, start date is a DateTime... You are not allowing the compiler make that decision for you... Also using Option Strict On allows you to catch a number of errors at compile time, instead of run time. Hope this helps Jay "tinman" <dw****@yahoo> wrote in message news:uh**************@TK2MSFTNGP12.phx.gbl... Hi... I have the following two excerpts from a method. It basically reads data from a DataReader and loads it in a collection. Excerpt A: ******** With ProjectData While .Read Me.Add(DirectCast(.Item("project_id"), Guid), _ DirectCast(.Item("start_date"), DateTime), _ DirectCast(.Item("end_date"), DateTime), _ DirectCast(.Item("priority"), Integer), _ DirectCast(.Item("description"), String), _ DirectCast(.Item("project_manager"), String) End While End With Excerpt B: ******** With ProjectData While .Read Me.Add(.Item("project_id"), .Item("start_date"), .Item("end_date"), .Item("priority"), .Item("description"), .Item("project_manager") End While End With Question: Does automatic casting outperform explicit casting ? When I run ILDASM, I find that at each DirectCast, there is unboxing but in Excerpt B, there isn''t any. Snippets of the ILDASM for Excerpt A and B below: ILDASM (Excerpt A) **************** IL_0098: ldloc.2 IL_0099: ldstr "description" IL_009e: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_00a3: unbox [mscorlib]System.Int32 IL_00a8: ldobj [mscorlib]System.Int32 ILDASM (Excerpt B) **************** IL_0092: ldloc.2 IL_0093: ldstr "description" IL_0098: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_009d: call int32 [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.IntegerType ::F romObject(object) Any pointers to articles that explain what goes on "under the hood" with regards to casting would be much appreciated as well. Cheers !thanks guys.... I believe the Get*Type* works better than the DirectCast approach. The resulting IL appears "leaner"... In the initial IL with DirectCast, I was afraid that all the unboxing would cause a performance concern since it was going to continue reading data in a loop (While .Read) ........ Cheers... "tinman" <dw****@yahoo> wrote in message news:uh**************@TK2MSFTNGP12.phx.gbl... Hi... I have the following two excerpts from a method. It basically reads data from a DataReader and loads it in a collection. Excerpt A: ******** With ProjectData While .Read Me.Add(DirectCast(.Item("project_id"), Guid), _ DirectCast(.Item("start_date"), DateTime), _ DirectCast(.Item("end_date"), DateTime), _ DirectCast(.Item("priority"), Integer), _ DirectCast(.Item("description"), String), _ DirectCast(.Item("project_manager"), String) End While End With Excerpt B: ******** With ProjectData While .Read Me.Add(.Item("project_id"), .Item("start_date"), .Item("end_date"), .Item("priority"), .Item("description"), .Item("project_manager") End While End With Question: Does automatic casting outperform explicit casting ? When I run ILDASM, I find that at each DirectCast, there is unboxing but in Excerpt B, there isn''t any. Snippets of the ILDASM for Excerpt A and B below: ILDASM (Excerpt A) **************** IL_0098: ldloc.2 IL_0099: ldstr "description" IL_009e: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_00a3: unbox [mscorlib]System.Int32 IL_00a8: ldobj [mscorlib]System.Int32 ILDASM (Excerpt B) **************** IL_0092: ldloc.2 IL_0093: ldstr "description" IL_0098: callvirt instance object XXX.Projects.XDataReader::get_Item(string) IL_009d: call int32 [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.IntegerType ::F romObject(object) Any pointers to articles that explain what goes on "under the hood" with regards to casting would be much appreciated as well. Cheers !更多推荐
哪种方法优于另一种方法？
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