開發中靈活使用屬性類

什麼是屬性類？

        從抽象類System.Attribute派生出來的類（無論是直接的還是間接的）都稱為屬性類（MSDN中的定義）。

        屬性類的名稱一般都帶有Attribute字尾，但使用的時候可以包含也可以忽略，如果你自己起的名字沒有這個字尾，則需要全稱來區分了。如果不怕輸入麻煩，建議還是不管是否有字尾，都輸入全稱為好，這樣可以減少歧義。

        在.NET架構中差不多定義了200個Attribute相關類，可見Attribute的應用十分廣泛，它的全圖在MSDN中如下：

System.Object

   System.Attribute

      System.AttributeUsageAttribute

      System.CLSCompliantAttribute

      System.ComponentModel.AmbientValueAttribute

      System.ComponentModel.BindableAttribute

      System.ComponentModel.BrowsableAttribute

      System.ComponentModel.CategoryAttribute

      System.ComponentModel.DefaultEventAttribute

      System.ComponentModel.DefaultPropertyAttribute

      System.ComponentModel.DefaultValueAttribute

      System.ComponentModel.DescriptionAttribute

      System.ComponentModel.Design.Serialization.DesignerSerializerAttribute

      System.ComponentModel.Design.Serialization.RootDesignerSerializerAttribute

      System.ComponentModel.DesignerAttribute

      System.ComponentModel.DesignerCategoryAttribute

      System.ComponentModel.DesignerSerializationVisibilityAttribute

      System.ComponentModel.DesignOnlyAttribute

      System.ComponentModel.DesignTimeVisibleAttribute

      System.ComponentModel.EditorAttribute

      System.ComponentModel.EditorBrowsableAttribute

      System.ComponentModel.ImmutableObjectAttribute

      System.ComponentModel.InheritanceAttribute

      System.ComponentModel.InstallerTypeAttribute

      System.ComponentModel.LicenseProviderAttribute

      System.ComponentModel.ListBindableAttribute

      System.ComponentModel.LocalizableAttribute

      System.ComponentModel.MergablePropertyAttribute

      System.ComponentModel.NotifyParentPropertyAttribute

      System.ComponentModel.ParenthesizePropertyNameAttribute

      System.ComponentModel.PropertyTabAttribute

      System.ComponentModel.ProvidePropertyAttribute

      System.ComponentModel.ReadOnlyAttribute

      System.ComponentModel.RecommendedAsConfigurableAttribute

      System.ComponentModel.RefreshPropertiesAttribute

      System.ComponentModel.RunInstallerAttribute

      System.ComponentModel.ToolboxItemAttribute

      System.ComponentModel.ToolboxItemFilterAttribute

      System.ComponentModel.TypeConverterAttribute

      System.ContextStaticAttribute

      System.Diagnostics.ConditionalAttribute

      System.Diagnostics.DebuggableAttribute

      System.Diagnostics.DebuggerHiddenAttribute

      System.Diagnostics.DebuggerStepThroughAttribute

      System.Drawing.ToolboxBitmapAttribute

      System.EnterpriseServices.ApplicationAccessControlAttribute

      System.EnterpriseServices.ApplicationActivationAttribute

      System.EnterpriseServices.ApplicationIDAttribute

      System.EnterpriseServices.ApplicationNameAttribute

      System.EnterpriseServices.ApplicationQueuingAttribute

      System.EnterpriseServices.AutoCompleteAttribute

      System.EnterpriseServices.CompensatingResourceManager.ApplicationCrmEnabledAttribute

      System.EnterpriseServices.ComponentAccessControlAttribute

      System.EnterpriseServices.COMTIIntrinsicsAttribute

      System.EnterpriseServices.ConstructionEnabledAttribute

      System.EnterpriseServices.DescriptionAttribute

      System.EnterpriseServices.EventClassAttribute

      System.EnterpriseServices.EventTrackingEnabledAttribute

      System.EnterpriseServices.ExceptionClassAttribute

      System.EnterpriseServices.IISIntrinsicsAttribute

      System.EnterpriseServices.InterfaceQueuingAttribute

      System.EnterpriseServices.JustInTimeActivationAttribute

      System.EnterpriseServices.LoadBalancingSupportedAttribute

      System.EnterpriseServices.MustRunInClientContextAttribute

      System.EnterpriseServices.ObjectPoolingAttribute

      System.EnterpriseServices.PrivateComponentAttribute

      System.EnterpriseServices.SecureMethodAttribute

      System.EnterpriseServices.SecurityRoleAttribute

      System.EnterpriseServices.SynchronizationAttribute

      System.EnterpriseServices.TransactionAttribute

      System.FlagsAttribute

      System.LoaderOptimizationAttribute

      System.Management.Instrumentation.IgnoreMemberAttribute

      System.Management.Instrumentation.InstrumentationClassAttribute

      System.Management.Instrumentation.InstrumentedAttribute

      System.Management.Instrumentation.ManagedNameAttribute

      System.MTAThreadAttribute

      System.NonSerializedAttribute

      System.ObsoleteAttribute

      System.ParamArrayAttribute

      System.Reflection.AssemblyAlgorithmIdAttribute

      System.Reflection.AssemblyCompanyAttribute

      System.Reflection.AssemblyConfigurationAttribute

      System.Reflection.AssemblyCopyrightAttribute

      System.Reflection.AssemblyCultureAttribute

      System.Reflection.AssemblyDefaultAliasAttribute

      System.Reflection.AssemblyDelaySignAttribute

      System.Reflection.AssemblyDescriptionAttribute

      System.Reflection.AssemblyFileVersionAttribute

      System.Reflection.AssemblyFlagsAttribute

      System.Reflection.AssemblyInformationalVersionAttribute

      System.Reflection.AssemblyKeyFileAttribute

      System.Reflection.AssemblyKeyNameAttribute

      System.Reflection.AssemblyProductAttribute

      System.Reflection.AssemblyTitleAttribute

      System.Reflection.AssemblyTrademarkAttribute

      System.Reflection.AssemblyVersionAttribute

      System.Reflection.DefaultMemberAttribute

      System.Resources.NeutralResourcesLanguageAttribute

      System.Resources.SatelliteContractVersionAttribute

      System.Runtime.CompilerServices.AccessedThroughPropertyAttribute

      System.Runtime.CompilerServices.CompilationRelaxationsAttribute

      System.Runtime.CompilerServices.CompilerGlobalScopeAttribute

      System.Runtime.CompilerServices.CustomConstantAttribute

      System.Runtime.CompilerServices.DecimalConstantAttribute

      System.Runtime.CompilerServices.DiscardableAttribute

      System.Runtime.CompilerServices.IndexerNameAttribute

      System.Runtime.CompilerServices.MethodImplAttribute

      System.Runtime.CompilerServices.RequiredAttributeAttribute

      System.Runtime.InteropServices.AutomationProxyAttribute

      System.Runtime.InteropServices.BestFitMappingAttribute

      System.Runtime.InteropServices.ClassInterfaceAttribute

      System.Runtime.InteropServices.CoClassAttribute

      System.Runtime.InteropServices.ComAliasNameAttribute

      System.Runtime.InteropServices.ComCompatibleVersionAttribute

      System.Runtime.InteropServices.ComConversionLossAttribute

      System.Runtime.InteropServices.ComEventInterfaceAttribute

      System.Runtime.InteropServices.ComImportAttribute

      System.Runtime.InteropServices.ComRegisterFunctionAttribute

      System.Runtime.InteropServices.ComSourceInterfacesAttribute

      System.Runtime.InteropServices.ComUnregisterFunctionAttribute

      System.Runtime.InteropServices.ComVisibleAttribute

      System.Runtime.InteropServices.DispIdAttribute

      System.Runtime.InteropServices.DllImportAttribute

      System.Runtime.InteropServices.FieldOffsetAttribute

      System.Runtime.InteropServices.GuidAttribute

      System.Runtime.InteropServices.IDispatchImplAttribute

      System.Runtime.InteropServices.ImportedFromTypeLibAttribute

      System.Runtime.InteropServices.InAttribute

      System.Runtime.InteropServices.InterfaceTypeAttribute

      System.Runtime.InteropServices.LCIDConversionAttribute

      System.Runtime.InteropServices.MarshalAsAttribute

      System.Runtime.InteropServices.OptionalAttribute

      System.Runtime.InteropServices.OutAttribute

      System.Runtime.InteropServices.PreserveSigAttribute

      System.Runtime.InteropServices.PrimaryInteropAssemblyAttribute

      System.Runtime.InteropServices.ProgIdAttribute

      System.Runtime.InteropServices.StructLayoutAttribute

      System.Runtime.InteropServices.TypeLibFuncAttribute

      System.Runtime.InteropServices.TypeLibTypeAttribute

      System.Runtime.InteropServices.TypeLibVarAttribute

      System.Runtime.InteropServices.TypeLibVersionAttribute

      System.Runtime.Remoting.Messaging.OneWayAttribute

      System.Runtime.Remoting.Metadata.SoapAttribute

      System.Runtime.Remoting.Proxies.ProxyAttribute

      System.Security.AllowPartiallyTrustedCallersAttribute

      System.Security.Permissions.SecurityAttribute

      System.Security.SuppressUnmanagedCodeSecurityAttribute

      System.Security.UnverifiableCodeAttribute

      System.SerializableAttribute

      System.STAThreadAttribute

      System.ThreadStaticAttribute

      System.Web.Services.Configuration.XmlFormatExtensionAttribute

      System.Web.Services.Configuration.XmlFormatExtensionPointAttribute

      System.Web.Services.Configuration.XmlFormatExtensionPrefixAttribute

      System.Web.Services.Protocols.HttpMethodAttribute

      System.Web.Services.Protocols.MatchAttribute

      System.Web.Services.Protocols.SoapDocumentMethodAttribute

      System.Web.Services.Protocols.SoapDocumentServiceAttribute

      System.Web.Services.Protocols.SoapExtensionAttribute

      System.Web.Services.Protocols.SoapHeaderAttribute

      System.Web.Services.Protocols.SoapRpcMethodAttribute

      System.Web.Services.Protocols.SoapRpcServiceAttribute

      System.Web.Services.WebMethodAttribute

      System.Web.Services.WebServiceAttribute

      System.Web.Services.WebServiceBindingAttribute

      System.Web.UI.ConstructorNeedsTagAttribute

      System.Web.UI.ControlBuilderAttribute

      System.Web.UI.DataBindingHandlerAttribute

      System.Web.UI.ParseChildrenAttribute

      System.Web.UI.PartialCachingAttribute

      System.Web.UI.PersistChildrenAttribute

      System.Web.UI.PersistenceModeAttribute

      System.Web.UI.TagPrefixAttribute

      System.Web.UI.TemplateContainerAttribute

      System.Web.UI.ToolboxDataAttribute

      System.Web.UI.ValidationPropertyAttribute

      System.Xml.Serialization.SoapAttributeAttribute

      System.Xml.Serialization.SoapElementAttribute

      System.Xml.Serialization.SoapEnumAttribute

      System.Xml.Serialization.SoapIgnoreAttribute

      System.Xml.Serialization.SoapIncludeAttribute

      System.Xml.Serialization.SoapTypeAttribute

      System.Xml.Serialization.XmlAnyAttributeAttribute

      System.Xml.Serialization.XmlAnyElementAttribute

      System.Xml.Serialization.XmlArrayAttribute

      System.Xml.Serialization.XmlArrayItemAttribute

      System.Xml.Serialization.XmlAttributeAttribute

      System.Xml.Serialization.XmlChoiceIdentifierAttribute

      System.Xml.Serialization.XmlElementAttribute

      System.Xml.Serialization.XmlEnumAttribute

      System.Xml.Serialization.XmlIgnoreAttribute

      System.Xml.Serialization.XmlIncludeAttribute

      System.Xml.Serialization.XmlNamespaceDeclarationsAttribute

      System.Xml.Serialization.XmlRootAttribute

      System.Xml.Serialization.XmlTextAttribute

      System.Xml.Serialization.XmlTypeAttribute

System.STAThreadAttribute

       大家在一般使用中會留意到這個屬性嗎？用VS.NET建立一個項目，往往在main前面會如下面所示：

        /// <summary>

        /// 應用程式的主入口點。

        /// </summary>

        [STAThread]

        static void Main() 

        {

            Application.Run(new frmMain());

        }

       其實這個就是屬性類STAThreadAttribute了，它的作用表示應用程式的COM線程模型是單線程單元（STA）。

屬性類的實用性：

1.利用XML相關的屬性類，将相關業務類XML序列化，可以達到儲存狀态和遠端傳輸交換類資訊等作用。

共14個和XML相關的屬性類：

System.Xml.Serialization.XmlAnyAttributeAttribute

System.Xml.Serialization.XmlAnyElementAttribute 

System.Xml.Serialization.XmlArrayAttribute

System.Xml.Serialization.XmlArrayItemAttribute

System.Xml.Serialization.XmlAttributeAttribute

System.Xml.Serialization.XmlChoiceIdentifierAttribute

System.Xml.Serialization.XmlElementAttribute

System.Xml.Serialization.XmlEnumAttribute

System.Xml.Serialization.XmlIgnoreAttribute

System.Xml.Serialization.XmlIncludeAttribute

System.Xml.Serialization.XmlNamespaceDeclarationsAttribute

System.Xml.Serialization.XmlRootAttribute

System.Xml.Serialization.XmlTextAttribute

System.Xml.Serialization.XmlTypeAttribute

        最近做一個項目，需要将一些界面輸入的有一定結構規律的資訊儲存起來，然後下次需要時候可以調入到對應的界面位置上使用。（其實這個是很多應用都會碰到的）。結構和UI的對應關系可能會經常變動的，而且結構中需要填寫的内容不是所有都必須的，直接用關系型資料庫來儲存似乎不是太好的方案。首先想到就是用XML檔案來儲存這些資訊了，而界面之間的資訊顯示是有關聯的，可以說需要一個緩沖來記錄這些資訊，想到的就是定義一個類來記錄和操作這些資訊。這自然遇到一個問題，如何保持類和XML資料的同步呢？

        生成的XML檔案需要給其它業務來做處理，格式上有一定的規範，對于類來說，資訊都儲存在字段或者屬性那裡的，并沒有差別，但XML中可能有些資訊是Attribute,有些又是Element的。如何靈活地處理這些關系呢？用與XML相關的屬性來定義這些字段和類就可以了。

(1) 類資訊序列化到XML檔案中的代碼

        public void SerializeObject(string filename)

            XmlSerializer s = new XmlSerializer(typeof(Tables));

            TextWriter writer = new StreamWriter(filename);

            Tables group = new Tables();

            group.GroupID = 10.089f;

            group.IsActive = false;     

            group.HexBytes = new byte[1]{Convert.ToByte(100)};

            Employee x = new Employee();

            Employee y = new Employee();

            x.Name = "Jack";

            y.Name = "Jill";

            x.des2 = "Yyyy

";

            x.colType = new ColumnType[2];

            x.colType[0] = new ColumnType();

            x.colType[1] = new ColumnType();

            x.colType[0].linkField = "Haaa

            x.colType[1].linkType = "Zzzz

            y.Age[0] = 20;

            y.Age[1] = 40;

            y.Desc = "OK";

            group.Employees = new Employee[2]{x,y};

            Manager mgr = new Manager();

            mgr.Name = "Sara";

            mgr.Level = 4;

            mgr.Desc = "Yes";

            mgr.aHead = true;

            group.Manager = mgr;

            group.ExtraInfo = new ArrayList();

            group.ExtraInfo.Add(42);

            group.ExtraInfo.Add("Answer");

            s.Serialize(writer, group);

            writer.Close();

(2) XML檔案資訊變成類的資訊的代碼

        public void DeserializeObject(string filename)

            FileStream fs = new FileStream(filename, FileMode.Open);

            XmlSerializer x = new XmlSerializer(typeof(Tables));

            Tables g = (Tables) x.Deserialize(fs);

            int i=0;

              foreach(Employee e in g.Employees)

            {

                i = i + 1;

                Console.WriteLine("No {0} Name: {1}",i.ToString(),e.Name);

            }

            Console.WriteLine(g.Manager.Name);

            Console.WriteLine(g.GroupID);

            Console.WriteLine(g.HexBytes[0]);

(3)例子中相關類資訊生成的XML檔案

<?xml version="1.0" encoding="utf-8"?>

<Tables xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <Member>

    <Employee AHead="false">

      <Name>Jack</Name>

      <Age>0</Age>

      <des2>Yyyy

</des2>

      <ColumnType LinkField="Haaa

" />

      <ColumnType LinkType="Zzzz

    </Employee>

    <Employee Desc="OK" AHead="false">

      <Name>Jill</Name>

      <Age>20</Age>

      <Age>40</Age>

  </Member>

  <Building>10.088999748229981</Building>

  <HexBytes>64</HexBytes>

  <IsActive>false</IsActive>

  <Manager Desc="Yes" AHead="true">

    <Name>Sara</Name>

    <Age>0</Age>

    <Level>4</Level>

  </Manager>

  <ObjectNumber>42</ObjectNumber>

  <ObjectString>Answer</ObjectString>

</Tables>

(4) XML總體架構如何用XML相關屬性類描述

    public class Tables

    {

        [XmlArray(ElementName = "Member")]

        public Employee[] Employees;

        [XmlElement(DataType = "double",

             ElementName = "Building")]

        public double GroupID;

        [XmlElement(DataType = "hexBinary")]

        public byte [] HexBytes;

        [XmlElement(DataType = "boolean")]

        public bool IsActive;

        [XmlElement(Type = typeof(Manager))]

        public Employee Manager;

        [XmlElement(typeof(int),

             ElementName = "ObjectNumber"),

        XmlElement(typeof(string),

            ElementName = "ObjectString")]

        public ArrayList ExtraInfo;

    }   

(5) 類的字段資訊表示為屬性的方法

    public class Employee

        public string Name;

        [XmlElement(typeof(int))]

        public int[] Age = new int[2];

        [XmlAttribute(AttributeName = "Desc")]

        public string Desc;

        [XmlAttribute(AttributeName = "AHead")]

        public bool aHead;

        public string des2;

        [XmlElement(ElementName="ColumnType")]

        public ColumnType[] colType;

    }

2.自己根據需要定義自己的屬性類，例如定義相關業務類和UI的關系。

在使用中，資訊不是一個UI就完成的，可能經過了幾個UI，或者幾個頁面去互動，但可能業務的調整，顯示的位置或者一些參數可能需要調整的，這些UI的資訊能否也定義為類的某些屬性？

從.NET的Attribute派生一個客戶定制類可以輕松做到這點，定制類隻需要從System.Attribute派生即可。

    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Class,AllowMultiple=true)]

    public class LayoutAttribute : Attribute

        string m_desc;

        public string OwnPage;

        public string GetDesc()

            return m_desc;

        public LayoutAttribute(string strDesc)

           m_desc = strDesc;

       AttributeUsage這個類定義了LayoutAttribute的一些基本資訊，例如這裡定義了LayoutAttribute适用于字段，類，并且允許重複定義的。

       在應用中，可以利用反射機制，将這些定義的資訊擷取，進而判斷應該在界面上如何處理了。

            Type myType = Type.GetType("testXmlAttr.Manager");

            Console.WriteLine(myType.FullName);

            FieldInfo myFieldInfo = myType.GetField("Level");

            object[] atts = myFieldInfo.GetCustomAttributes(false);            

            for (int i=0;i<atts.Length;i++)

                Console.WriteLine(((LayoutAttribute)atts[i]).OwnPage);

例子運作結果：（同時在目前目錄下生成testXmlAttr.xml）

本文轉自風前絮~~部落格園部落格，原文連結：http://www.cnblogs.com/windsails/archive/2004/09/08/41006.html，如需轉載請自行聯系原作者