AttributesAttributesareanextensiblemechanismforaddingcustominformationtocodeelements(AttributeTargets:assemblies,types,members,returnvalues,andparameters).AnattributeisdefinedbyaclassthatinheritsfromtheabstractclassSystem.Attribute.ApplyingAnAttribute[Obsolete]publicclassFoo{...}[MyAttribute("Simpleclass","Version3.57")]//AttributewithparameterspublicclassMyOtherClass{}Predefined,ReservedAttributesTheObsoleteAttribute[Obsolete("UsemethodSuperPrintOut")]//producingwarningmessagestaticvoidPrintOut(stringstr){Console.WriteLine(str);}staticvoidMain(string[]args){PrintOut("LIU");}[Obsolete("UsemethodSuperPrintOut“,true)]//producingerrormessageTheConditionalAttributeTherulesforusingtheConditionalattributeonamethodarethefollowing:?Themethodmustbeamethodofaclassorstruct.?Themethodmustbeoftypevoid.?Themethodcannotbedeclaredasanoverride,butitcanbe

markedasvirtual.?Themethodcannotbetheimplementationofaninterface

method.ExampleofConditional#defineDoTraceclassProgram{[Conditional("DoTrace")]staticvoidTraceMessage(stringstr){Console.WriteLine(str);}staticvoidMain(){TraceMessage("StartofMain");Console.WriteLine("DoingworkinMain.");TraceMessage("EndofMain");}}TheCallerInformationAttributesThethreeattributenamesareCallerFilePath,CallerLineNumber,andCallerMemberName.Theseattributescanonlybeusedwithoptionalparametersonmethods.ExampleofCallerattributespublicstaticvoidMyTrace(stringmessage,[CallerFilePath]stringfileName="",[CallerLineNumber]intlineNumber=0,[CallerMemberName]stringcallingMember=""){Console.WriteLine($"File:{fileName}");Console.WriteLine($"Line:{lineNumber}");Console.WriteLine($"CalledFrom:{callingMember}");Console.WriteLine($"Message:{message}");}publicstaticvoidMain(){MyTrace("Simplemessage");}CLSCompliantDeclaresthatthepubliclyexposedmembersshouldbecheckedbythecompilerforcompliancewiththeCLS.

Compliantassembliescanbeusedbyany.NET-

compliantlanguage.SerializableDeclaresthattheconstructcanbeserialized.NonSerializedDeclaresthattheconstructcannotbeserialized.DLLImportDeclaresthattheimplementationisunmanagedcode.WebMethodDeclaresthatthemethodshouldbeexposedaspartof

anXMLwebservice.AttributeUsageDeclareswhattypesofprogramconstructsthe

attributecanbeappliedto.Thisattributeisappliedto

attributedeclarations.Seriablizable[Seriabliezable]classPlayer{publicintcoin=0;publicintmoney=0;publicstringname=“”;}序列化數(shù)據(jù)usingSystem.Runtime.Seriablization;usingSystem.Runtime.Seriablization.Formatters.Binary;Playerplayer=newPlayer();player.coin=1;player.money=10;=“Liu”;Iformatterformatter=newBinaryFormatter();Streamstream=newFileStream(“data.bin”,//

stream~data.bin文件FileMode.Create,FileAccess.Write,FileShare.None);formatter.Serialize(stream,player);//player數(shù)據(jù)序列化為二進制數(shù)據(jù)stream.Close();反序列化Iformatterformatter=newBinaryFormatter();Streamstream=newFileStream(“data.bin”,FileMode.Open,FileAccess.Read,FileShare.Read);Playerplayer=(Player)formatter.Deserialize(stream);stream.Close();SpecifyingMultipleAttributesMultipleattributescanbespecifiedforasinglecodeelement,[Serializable,Obsolete,CLSCompliant(false)]publicclassBar{...}[Serializable][Obsolete][CLSCompliant(false)]publicclassBar{...}WritingCustomAttributes[AttributeUsage(AttributeTargets.Method)]publicsealedclassMyAttributeAttribute:Attribute//System.Attribute{

publicstringDescription;publicstringVersionNumber;publicTestAttribute(stringdesc=“”,stringver=“”)

{

Description=desc;VersionNumber=ver;

}}SpecifyingtheConstructorofAttributespublicclassFoo{[MyAttribute("Holdsavalue")]//withonestringpublicintMyField;[MyAttribute("Version1.3","GalenDaniel")]//withtwostringspublicvoidMyMethod(){}}

UsingtheConstructorApplyinganattributeisadeclarativestatementthatdoesnotdeterminewhenanobjectoftheattributeclassshouldbeconstructed.Thedeclarativestatementsays“Thisattributeisassociatedwiththistarget,andincasetheattributeneedstobeconstructed,usethisconstructor.”AccessinganAttributewecanaccesscustomattributesbytwomethodsofType:IsDefinedandGetCustomAttributes.IsDefined:determinewhetheraparticularattributeisappliedtoaparticularclass.UsingtheGetCustomAttributesMethodMyClassmc=newMyClass();Typet=mc.GetType();object[]AttArr=t.GetCustomAttributes(false);TheBooleanparameterspecifieswhethertosearchtheinheritancetreetofindtheattributes.publicsealedclassMyAttributeAttribute:System.Attribute

{publicstringdesc;publicstringver;publicMyAttributeAttribute(stringdesc="",stringver="")

{this.desc=desc;this.ver=ver;

}

}[MyAtt