Attribute.IsDefaultAttribute メソッド

.NET Framework クラス ライブラリ リファレンス

Attribute.IsDefaultAttribute メソッド

派生クラス内でオーバーライドされたときに、このインスタンスの値が派生クラスの既定値かどうかを示します。

名前空間: System
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

Public Overridable Function
 IsDefaultAttribute As Boolean

Visual Basic (使用法)

Dim instance As Attribute
Dim returnValue As Boolean

returnValue = instance.IsDefaultAttribute

C#

public virtual bool IsDefaultAttribute ()

C++

public:
virtual bool IsDefaultAttribute ()

J#

public boolean IsDefaultAttribute ()

JScript

public function IsDefaultAttribute () : boolean

戻り値
このインスタンスがクラスの既定の属性の場合は true。それ以外の場合は false。

解説

このクラスの既定の実装は、false を返します。この既定の実装は、そのクラスで使用できるように派生クラスに実装されている必要があります。

派生クラスでのこのメソッドの実装は、標準の既定値とこのインスタンスの値を比較します。次に、このインスタンスの値が標準の既定値と等しいかどうかを示すブール値を返します。通常、標準値はこの実装の定数として指定されているか、またはこの実装が使用するフィールドにプログラムによって格納されています。

使用例

IsDefaultAttribute の使用方法を次のコード例に示します。

Visual Basic

Imports System
Imports System.Reflection

Module DemoModule

    ' An enumeration of animals. Start at 1 (0 = uninitialized).
    Enum Animal
        ' Pets
        Dog = 1
        Cat
        Bird
    End Enum

    ' Visual Basic requires that the AttributeUsage be specified.
    ' A custom attribute to allow a target to have a pet.
    <AttributeUsage(AttributeTargets.Method)> _
    Public Class AnimalTypeAttribute
        Inherits Attribute

        ' The constructor is called when the attribute is set.
        Public Sub New(ByVal
 animal As Animal)
            Me.thePet = animal
        End Sub

        ' Provide a default constructor and make Dog the default.
        Public Sub New()
            thePet = Animal.Dog
        End Sub

        ' Keep a variable internally ...
        Protected thePet As Animal

        ' .. and show a copy to the outside world.
        Public Property Pet() As
 Animal
            Get
                Return thePet
            End Get
            Set(ByVal Value As
 Animal)
                thePet = Value
            End Set
        End Property

        ' Override IsDefaultAttribute to return the correct response.
        Public Overrides Function
 IsDefaultAttribute() As Boolean
            If thePet = Animal.Dog Then
                Return True
            Else
                Return False
            End If
        End Function

    End Class

    Public Class TestClass
        ' Use the default constructor.
        <AnimalType()> _
        Public Sub Method1()
        End Sub

    End Class

    Sub Main()
        ' Get the class type to access its metadata.
        Dim clsType As Type = GetType(TestClass)
        ' Get type information for the method.
        Dim mInfo As MethodInfo = clsType.GetMethod("Method1")
        ' Get the AnimalType attribute for the method.
        Dim attr As Attribute = Attribute.GetCustomAttribute(mInfo,
 _
            GetType(AnimalTypeAttribute))
        If Not attr Is Nothing
 And TypeOf attr Is AnimalTypeAttribute
 Then
            ' Convert the attribute to the required type.
            Dim atAttr As AnimalTypeAttribute
 = _
                CType(attr, AnimalTypeAttribute)
            Dim strDef As String
            ' Check to see if the default attribute is applied.
            If atAttr.IsDefaultAttribute() Then
                strDef = "is"
            Else
                strDef = "is not"
            End If
            ' Display the result.
            Console.WriteLine("The attribute {0} for method {1}
 " & _
                    "in class {2}", atAttr.Pet.ToString(),
 mInfo.Name, _
                    clsType.Name)
            Console.WriteLine("{0} the default for the AnimalType
 " & _
                    "attribute.", strDef)
        End If
    End Sub
End Module

C#

using System;
using System.Reflection;

namespace DefAttrCS 
{
    // An enumeration of animals. Start at 1 (0 = uninitialized).
    public enum Animal 
    {
        // Pets.
        Dog = 1,
        Cat,
        Bird,
    }

    // A custom attribute to allow a target to have a pet.
    public class AnimalTypeAttribute : Attribute
 
    {
        // The constructor is called when the attribute is set.
        public AnimalTypeAttribute(Animal pet) 
        {
            thePet = pet;
        }

        // Provide a default constructor and make Dog the default.
        public AnimalTypeAttribute() 
        {
            thePet = Animal.Dog;
        }

        // Keep a variable internally ...
        protected Animal thePet;

        // .. and show a copy to the outside world.
        public Animal Pet 
        {
            get { return thePet; }
            set { thePet = Pet; }
        }

        // Override IsDefaultAttribute to return the correct response.
        public override bool IsDefaultAttribute()
 
        {
            if (thePet == Animal.Dog)
                return true;

            return false;
        }
    }

    public class TestClass 
    {
        // Use the default constructor.
        [AnimalType]
        public void Method1()
        {}
    }

    class DemoClass 
    {
        static void Main(string[]
 args) 
        {
            // Get the class type to access its metadata.
            Type clsType = typeof(TestClass);
            // Get type information for the method.
            MethodInfo mInfo = clsType.GetMethod("Method1");
            // Get the AnimalType attribute for the method.
            AnimalTypeAttribute atAttr = 
                (AnimalTypeAttribute)Attribute.GetCustomAttribute(mInfo,
                typeof(AnimalTypeAttribute));
            // Check to see if the default attribute is applied.
            Console.WriteLine("The attribute {0} for method
 {1} in class {2}",
                atAttr.Pet, mInfo.Name, clsType.Name); 
            Console.WriteLine("{0} the default for
 the AnimalType attribute.", 
                atAttr.IsDefaultAttribute() ? "is" : "is not");
        }
    }
}

C++

using namespace System;
using namespace System::Reflection;

// An enumeration of animals. Start at 1 (0 = uninitialized).
public enum class Animal
{
   // Pets.
   Dog = 1,
   Cat, Bird
};


// A custom attribute to allow a target to have a pet.
public ref class AnimalTypeAttribute: public
 Attribute
{
public:

   // The constructor is called when the attribute is set.
   AnimalTypeAttribute( Animal pet )
   {
      thePet = pet;
   }

   // Provide a default constructor and make Dog the default.
   AnimalTypeAttribute()
   {
      thePet = Animal::Dog;
   }

protected:

   // Keep a variable internally ...
   Animal thePet;

public:

   property Animal Pet 
   {
      // .. and show a copy to the outside world.
      Animal get()
      {
         return thePet;
      }
      void set( Animal value )
      {
         thePet = value;
      }

   }

   // Override IsDefaultAttribute to return the correct response.
   virtual bool IsDefaultAttribute() override
   {
      return thePet == Animal::Dog;
   }
};

public ref class TestClass
{
public:

   // Use the default constructor.

   [AnimalType]
   void Method1(){}
};

int main()
{
   // Get the class type to access its metadata.
   Type^ clsType = TestClass::typeid;

   // Get type information for the method.
   MethodInfo^ mInfo = clsType->GetMethod( "Method1" );

   // Get the AnimalType attribute for the method.
   AnimalTypeAttribute^ atAttr = dynamic_cast<AnimalTypeAttribute^>(Attribute::GetCustomAttribute(
 mInfo, AnimalTypeAttribute::typeid ));

   // Check to see if the default attribute is applied.
   Console::WriteLine( "The attribute {0} for method {1}
 in class {2}", atAttr->Pet, mInfo->Name,
 clsType->Name );
   Console::WriteLine( "{0} the default for
 the AnimalType attribute.", atAttr->IsDefaultAttribute() ? (String^)"is"
 : "is not" );
}

J#

package ISelectionServiceExample; 

import System.*;
import System.Drawing.*;
import System.Collections.*;
import System.ComponentModel.*;
import System.ComponentModel.Design.*;
import System.Windows.Forms.*;

/*  This sample demonstrates using the ISelectionService
    interface to receive notification of selection change events.  
    The SelectionComponent control attempts to retrieve an instance 
    of the ISelectionService when it is sited. If it can, it attaches 
    event handlers for events provided by the service that display
    a message when a component is selected or deselected.

    To run this sample, add the SelectionComponent control to
 a Form and
    then select or deselect components in design mode to see the
 behavior 
    of the component change event handlers. 
 */
public class SelectionComponent extends System.Windows.Forms.UserControl
{    
    private System.Windows.Forms.TextBox tbox1;
    private ISelectionService selectionService;

    public SelectionComponent()
    {
        // Initialize control
        this.SuspendLayout();
        this.set_Name("SelectionComponent");
        this.set_Size(new System.Drawing.Size(608,
 296));
        this.tbox1 = new System.Windows.Forms.TextBox();
        this.tbox1.set_Location(new System.Drawing.Point(24,
 16));
        this.tbox1.set_Name("listBox1");
        this.tbox1.set_Multiline(true);
        this.tbox1.set_Size(new System.Drawing.Size(560,
 251));
        this.tbox1.set_TabIndex(0);
        this.get_Controls().Add(this.tbox1);
        this.ResumeLayout();
    } //SelectionComponent

    /** @property
     */
    public ISite get_Site()
    {
        return super.get_Site();
    } //get_Site

    /** @property 
     */
    public void set_Site(ISite value)
    {
        // The ISelectionService is available in design mode 
        // only, and only after the component is sited.
        if (selectionService != null) {
            // Because the selection service has been 
            // previously obtained, the component may be in 
            // the process of being resited. 
            // Detatch the previous selection change event 
            // handlers in case the new selection
            // service is a new service instance belonging to 
            // another design mode service host.
            selectionService.remove_SelectionChanged(
                new EventHandler(OnSelectionChanged));
            selectionService.remove_SelectionChanging(
                new EventHandler(OnSelectionChanging));
        }
        // Establish the new site for the component.
        super.set_Site(value);
        if (super.get_Site() == null) {
            return;
        }
        // The selection service is not available outside of 
        // design mode. A call requesting the service 
        // using GetService while not in design mode will 
        // return null.
        selectionService = ((ISelectionService)(this.get_Site().
            GetService(ISelectionService.class.ToType())));

        // If an instance of the ISelectionService was obtained, 
        // attach event handlers for the selection 
        // changing and selection changed events.
        if (selectionService != null) {
            // Add an event handler for the SelectionChanging 
            // and SelectionChanged events.
            selectionService.add_SelectionChanging(
                new EventHandler(OnSelectionChanging));
            selectionService.add_SelectionChanged(
                new EventHandler(OnSelectionChanged));
        }
    } //set_Site

    private void OnSelectionChanged(Object
 sender, EventArgs args)
    {
        tbox1.AppendText(("The selected component was changed.  "
            + "Selected components:\r\n    " 
            + GetSelectedComponents() + "\r\n"));
    } //OnSelectionChanged

    private void OnSelectionChanging(Object
 sender, EventArgs args)
    {
        tbox1.AppendText(("The selected component is changing. "
            + "Selected components:\r\n    " 
            + GetSelectedComponents() + "\r\n"));
    } //OnSelectionChanging

    private String GetSelectedComponents()
    {
        String selectedString = "";
        Object components[] = new Object[((ICollection)(selectionService.
            GetSelectedComponents())).get_Count()];
        ((ICollection)(selectionService.GetSelectedComponents())).
            CopyTo(components, 0);
        for (int i = 0; i < components.length;
 i++) {
            if (i != 0) {
                selectedString += "&& ";
            }
            if (((IComponent)(selectionService.get_PrimarySelection())).
 
                    Equals((IComponent)(components.get_Item(i)))) {
                selectedString += "PrimarySelection:";
            }
            selectedString += ((IComponent)(components.get_Item(i))).
                get_Site().get_Name() + " ";
        }
        return selectedString;
    } //GetSelectedComponents

    // Clean up any resources being used.
    protected void Dispose(boolean disposing)
    {
        // Detatch the event handlers for the selection service.
        if (selectionService != null) {
            selectionService.remove_SelectionChanging(
                new EventHandler(this.OnSelectionChanging));
            selectionService.remove_SelectionChanged(
                new EventHandler(this.OnSelectionChanged));
        }
        super.Dispose(disposing);
    } //Dispose
} //SelectionComponent

JScript

import System;
import System.Reflection;

package DefAttrJS {
    // An enumeration of animals. Start at 1 (0 = uninitialized).
    public enum Animal {
        // Pets.
        Dog = 1,
        Cat,
        Bird,
    }

    // A custom attribute to allow a target to have a pet.
    AttributeUsage(AttributeTargets.Method) public class
 AnimalTypeAttribute extends Attribute {
        // The constructor is called when the attribute is set.
        public function AnimalTypeAttribute(pet
 : Animal) {
            thePet = pet;
        }

        // Provide a default constructor and make Dog the default.
        public function AnimalTypeAttribute()
 {
            thePet = Animal.Dog;
        }

        // Keep a variable internally ...
        protected var thePet : Animal;

        // .. and show a copy to the outside world.
        public function get
 Pet() : Animal {
            return thePet;         
        }

        public function set
 Pet(value : Animal) {        
            thePet = value;
        }

        // Override IsDefaultAttribute to return the correct response.
        public override function IsDefaultAttribute()
 : boolean {
            return thePet == Animal.Dog;
        }
    }

    public class TestClass {
        // Use the default constructor.
        AnimalType public function Method1()
 : void
        {}
    }

    class DemoClass {
        static function Main() : void
  {
            // Get the class type to access its metadata.
            var clsType : Type  = TestClass;
            // Get type information for the method.
            var mInfo : MethodInfo = clsType.GetMethod("Method1");
            // Get the AnimalType attribute for the method.
            var atAttr : AnimalTypeAttribute = 
                AnimalTypeAttribute(Attribute.GetCustomAttribute(mInfo, AnimalTypeAttribute));
            // Check to see if the default attribute is applied.
            Console.WriteLine("The attribute {0} for method
 {1} in class {2}",
                atAttr.Pet, mInfo.Name, clsType.Name); 
            Console.WriteLine("{0} the default for
 the AnimalType attribute.", 
                atAttr.IsDefaultAttribute() ? "is" : "is not");
        }
    }
}

DefAttrJS.DemoClass.Main();

/*
 * Output:
 * The attribute Dog for method Method1 in class
 TestClass
 * is the default for the AnimalType attribute.
 */

プラットフォーム

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

バージョン情報

.NET Framework
サポート対象 : 2.0、1.1、1.0

参照

関連項目
Attribute クラス
Attribute メンバ
System 名前空間