PropertyDescriptor Classe

Definição

public ref class PropertyDescriptor abstract : System::ComponentModel::MemberDescriptor

public abstract class PropertyDescriptor : System.ComponentModel.MemberDescriptor

[System.Runtime.InteropServices.ComVisible(true)]
public abstract class PropertyDescriptor : System.ComponentModel.MemberDescriptor

type PropertyDescriptor = class
    inherit MemberDescriptor

[<System.Runtime.InteropServices.ComVisible(true)>]
type PropertyDescriptor = class
    inherit MemberDescriptor

Public MustInherit Class PropertyDescriptor
Inherits MemberDescriptor

Herança

Object

MemberDescriptor

PropertyDescriptor

Derivado

System.ComponentModel.DependencyPropertyDescriptor

System.ComponentModel.TypeConverter.SimplePropertyDescriptor

Atributos

ComVisibleAttribute

Exemplos

O exemplo de código a seguir é criado com base no exemplo na classe PropertyDescriptorCollection. Ele imprime as informações (categoria, descrição, nome de exibição) do texto de um botão em uma caixa de texto. Ele pressupõe que button1 e textbox1 tenham sido instanciados em um formulário.

// Creates a new collection and assign it the properties for button1.
PropertyDescriptorCollection^ properties = TypeDescriptor::GetProperties( button1 );

// Sets an PropertyDescriptor to the specific property.
System::ComponentModel::PropertyDescriptor^ myProperty = properties->Find( "Text", false );

// Prints the property and the property description.
textBox1->Text = String::Concat( myProperty->DisplayName, "\n" );
textBox1->Text = String::Concat( textBox1->Text, myProperty->Description, "\n" );
textBox1->Text = String::Concat( textBox1->Text, myProperty->Category, "\n" );

// Creates a new collection and assign it the properties for button1.
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(button1);

// Sets an PropertyDescriptor to the specific property.
System.ComponentModel.PropertyDescriptor myProperty = properties.Find("Text", false);

// Prints the property and the property description.
textBox1.Text = myProperty.DisplayName + '\n';
textBox1.Text += myProperty.Description + '\n';
textBox1.Text += myProperty.Category + '\n';

' Creates a new collection and assign it the properties for button1.
Dim properties As PropertyDescriptorCollection = TypeDescriptor.GetProperties(Button1)

' Sets an PropertyDescriptor to the specific property.
Dim myProperty As PropertyDescriptor = properties.Find("Text", False)

' Prints the property and the property description.
TextBox1.Text += myProperty.DisplayName & Microsoft.VisualBasic.ControlChars.Cr
TextBox1.Text += myProperty.Description & Microsoft.VisualBasic.ControlChars.Cr
TextBox1.Text += myProperty.Category & Microsoft.VisualBasic.ControlChars.Cr

O exemplo de código a seguir mostra como implementar um descritor de propriedade personalizado que fornece um wrapper somente leitura em torno de uma propriedade. O SerializeReadOnlyPropertyDescriptor é usado em um designer personalizado para fornecer um descritor de propriedade somente leitura para a propriedade Size do controle.

using System;
using System.Collections;
using System.ComponentModel;
using System.Text;

namespace ReadOnlyPropertyDescriptorTest
{
    // The SerializeReadOnlyPropertyDescriptor shows how to implement a 
    // custom property descriptor. It provides a read-only wrapper 
    // around the specified PropertyDescriptor. 
    internal sealed class SerializeReadOnlyPropertyDescriptor : PropertyDescriptor
    {
        private PropertyDescriptor _pd = null;

        public SerializeReadOnlyPropertyDescriptor(PropertyDescriptor pd)
            : base(pd)
        {
            this._pd = pd;
        }

        public override AttributeCollection Attributes
        {
            get
            {
                return( AppendAttributeCollection(
                    this._pd.Attributes, 
                    ReadOnlyAttribute.Yes) );
            }
        }

        protected override void FillAttributes(IList attributeList)
        {
            attributeList.Add(ReadOnlyAttribute.Yes);
        }

        public override Type ComponentType
        {
            get
            {
                return this._pd.ComponentType;
            }
        }

        // The type converter for this property.
        // A translator can overwrite with its own converter.
        public override TypeConverter Converter
        {
            get
            {
                return this._pd.Converter;
            }
        }

        // Returns the property editor 
        // A translator can overwrite with its own editor.
        public override object GetEditor(Type editorBaseType)
        {
            return this._pd.GetEditor(editorBaseType);
        }

        // Specifies the property is read only.
        public override bool IsReadOnly
        {
            get
            {
                return true;
            }
        }

        public override Type PropertyType
        {
            get
            {
                return this._pd.PropertyType;
            }
        }

        public override bool CanResetValue(object component)
        {
            return this._pd.CanResetValue(component);
        }

        public override object GetValue(object component)
        {
            return this._pd.GetValue(component);
        }

        public override void ResetValue(object component)
        {
            this._pd.ResetValue(component);
        }

        public override void SetValue(object component, object val)
        {
            this._pd.SetValue(component, val);
        }

        // Determines whether a value should be serialized.
        public override bool ShouldSerializeValue(object component)
        {
            bool result = this._pd.ShouldSerializeValue(component);

            if (!result)
            {
                DefaultValueAttribute dva = (DefaultValueAttribute)_pd.Attributes[typeof(DefaultValueAttribute)];
                if (dva != null)
                {
                    result = !Object.Equals(this._pd.GetValue(component), dva.Value);
                }
                else
                {
                    result = true;
                }
            }

            return result;
        }

        // The following Utility methods create a new AttributeCollection
        // by appending the specified attributes to an existing collection.
        static public AttributeCollection AppendAttributeCollection(
            AttributeCollection existing, 
            params Attribute[] newAttrs)
        {
            return new AttributeCollection(AppendAttributes(existing, newAttrs));
        }

        static public Attribute[] AppendAttributes(
            AttributeCollection existing, 
            params Attribute[] newAttrs)
        {
            if (existing == null)
            {
                throw new ArgumentNullException(nameof(existing));
            }

            newAttrs ??= new Attribute[0];

            Attribute[] attributes;

            Attribute[] newArray = new Attribute[existing.Count + newAttrs.Length];
            int actualCount = existing.Count;
            existing.CopyTo(newArray, 0);

            for (int idx = 0; idx < newAttrs.Length; idx++)
            {
                if (newAttrs[idx] == null)
                {
                    throw new ArgumentNullException("newAttrs");
                }

                // Check if this attribute is already in the existing
                // array.  If it is, replace it.
                bool match = false;
                for (int existingIdx = 0; existingIdx < existing.Count; existingIdx++)
                {
                    if (newArray[existingIdx].TypeId.Equals(newAttrs[idx].TypeId))
                    {
                        match = true;
                        newArray[existingIdx] = newAttrs[idx];
                        break;
                    }
                }

                if (!match)
                {
                    newArray[actualCount++] = newAttrs[idx];
                }
            }

            // If some attributes were collapsed, create a new array.
            if (actualCount < newArray.Length)
            {
                attributes = new Attribute[actualCount];
                Array.Copy(newArray, 0, attributes, 0, actualCount);
            }
            else
            {
                attributes = newArray;
            }

            return attributes;
        }
    }
}

Imports System.Collections
Imports System.ComponentModel
Imports System.Text

' The SerializeReadOnlyPropertyDescriptor shows how to implement a 
' custom property descriptor. It provides a read-only wrapper 
' around the specified PropertyDescriptor. 
Friend NotInheritable Class SerializeReadOnlyPropertyDescriptor
    Inherits PropertyDescriptor
    Private _pd As PropertyDescriptor = Nothing


    Public Sub New(ByVal pd As PropertyDescriptor)
        MyBase.New(pd)
        Me._pd = pd

    End Sub


    Public Overrides ReadOnly Property Attributes() As AttributeCollection
        Get
            Return AppendAttributeCollection(Me._pd.Attributes, ReadOnlyAttribute.Yes)
        End Get
    End Property


    Protected Overrides Sub FillAttributes(ByVal attributeList As IList)
        attributeList.Add(ReadOnlyAttribute.Yes)

    End Sub


    Public Overrides ReadOnly Property ComponentType() As Type
        Get
            Return Me._pd.ComponentType
        End Get
    End Property


    ' The type converter for this property.
    ' A translator can overwrite with its own converter.
    Public Overrides ReadOnly Property Converter() As TypeConverter
        Get
            Return Me._pd.Converter
        End Get
    End Property


    ' Returns the property editor 
    ' A translator can overwrite with its own editor.
    Public Overrides Function GetEditor(ByVal editorBaseType As Type) As Object
        Return Me._pd.GetEditor(editorBaseType)

    End Function

    ' Specifies the property is read only.
    Public Overrides ReadOnly Property IsReadOnly() As Boolean
        Get
            Return True
        End Get
    End Property


    Public Overrides ReadOnly Property PropertyType() As Type
        Get
            Return Me._pd.PropertyType
        End Get
    End Property


    Public Overrides Function CanResetValue(ByVal component As Object) As Boolean
        Return Me._pd.CanResetValue(component)

    End Function


    Public Overrides Function GetValue(ByVal component As Object) As Object
        Return Me._pd.GetValue(component)

    End Function


    Public Overrides Sub ResetValue(ByVal component As Object)
        Me._pd.ResetValue(component)

    End Sub


    Public Overrides Sub SetValue(ByVal component As Object, ByVal val As Object)
        Me._pd.SetValue(component, val)

    End Sub

    ' Determines whether a value should be serialized.
    Public Overrides Function ShouldSerializeValue(ByVal component As Object) As Boolean
        Dim result As Boolean = Me._pd.ShouldSerializeValue(component)

        If Not result Then
            Dim dva As DefaultValueAttribute = _
                CType(_pd.Attributes(GetType(DefaultValueAttribute)), DefaultValueAttribute)
            If Not (dva Is Nothing) Then
                result = Not [Object].Equals(Me._pd.GetValue(component), dva.Value)
            Else
                result = True
            End If
        End If

        Return result

    End Function


    ' The following Utility methods create a new AttributeCollection
    ' by appending the specified attributes to an existing collection.
    Public Shared Function AppendAttributeCollection( _
        ByVal existing As AttributeCollection, _
        ByVal ParamArray newAttrs() As Attribute) As AttributeCollection

        Return New AttributeCollection(AppendAttributes(existing, newAttrs))

    End Function

    Public Shared Function AppendAttributes( _
        ByVal existing As AttributeCollection, _
        ByVal ParamArray newAttrs() As Attribute) As Attribute()

        If existing Is Nothing Then
            Throw New ArgumentNullException("existing")
        End If

        If newAttrs Is Nothing Then
            newAttrs = New Attribute(-1) {}
        End If

        Dim attributes() As Attribute

        Dim newArray(existing.Count + newAttrs.Length) As Attribute
        Dim actualCount As Integer = existing.Count
        existing.CopyTo(newArray, 0)

        Dim idx As Integer
        For idx = 0 To newAttrs.Length
            If newAttrs(idx) Is Nothing Then
                Throw New ArgumentNullException("newAttrs")
            End If

            ' Check if this attribute is already in the existing
            ' array.  If it is, replace it.
            Dim match As Boolean = False
            Dim existingIdx As Integer
            For existingIdx = 0 To existing.Count - 1
                If newArray(existingIdx).TypeId.Equals(newAttrs(idx).TypeId) Then
                    match = True
                    newArray(existingIdx) = newAttrs(idx)
                    Exit For
                End If
            Next existingIdx

            If Not match Then
                actualCount += 1
                newArray(actualCount) = newAttrs(idx)
            End If
        Next idx

        ' If some attributes were collapsed, create a new array.
        If actualCount < newArray.Length Then
            attributes = New Attribute(actualCount) {}
            Array.Copy(newArray, 0, attributes, 0, actualCount)
        Else
            attributes = newArray
        End If

        Return attributes

    End Function
End Class

Os exemplos de código a seguir mostram como usar o SerializeReadOnlyPropertyDescriptor em um designer personalizado.

using System.Collections;
using System.ComponentModel;
using System.Windows.Forms.Design;

namespace ReadOnlyPropertyDescriptorTest
{
    class DemoControlDesigner : ControlDesigner
    {
        // The PostFilterProperties method replaces the control's 
        // Size property with a read-only Size property by using 
        // the SerializeReadOnlyPropertyDescriptor class.
        protected override void PostFilterProperties(IDictionary properties)
        {
            if (properties.Contains("Size"))
            {
                PropertyDescriptor original = properties["Size"] as PropertyDescriptor;
                SerializeReadOnlyPropertyDescriptor readOnlyDescriptor = 
                    new SerializeReadOnlyPropertyDescriptor(original);

                properties["Size"] = readOnlyDescriptor;
            }

            base.PostFilterProperties(properties);
        }
    }
}

Imports System.Collections
Imports System.ComponentModel
Imports System.Text
Imports System.Windows.Forms.Design

Class DemoControlDesigner
    Inherits ControlDesigner
    
    ' The PostFilterProperties method replaces the control's 
    ' Size property with a read-only Size property by using 
    ' the SerializeReadOnlyPropertyDescriptor class.
    Protected Overrides Sub PostFilterProperties(ByVal properties As IDictionary) 
        If properties.Contains("Size") Then
            Dim original As PropertyDescriptor = properties("Size")
            
            Dim readOnlyDescriptor As New SerializeReadOnlyPropertyDescriptor(original)
            
            properties("Size") = readOnlyDescriptor
        End If
        
        MyBase.PostFilterProperties(properties)
    
    End Sub
End Class

using System.ComponentModel;
using System.Windows.Forms;

namespace ReadOnlyPropertyDescriptorTest
{
    [Designer(typeof(DemoControlDesigner))]
    public class DemoControl : Control
    {
        public DemoControl()
        {
        }
    }
}

Imports System.ComponentModel
Imports System.ComponentModel.Design
Imports System.Text
Imports System.Windows.Forms
Imports System.Windows.Forms.Design


<Designer(GetType(DemoControlDesigner))>  _
Public Class DemoControl
    Inherits Control
    
    Public Sub New() 
    
    End Sub
End Class

Comentários

Uma descrição de uma propriedade consiste em um nome, seus atributos, a classe de componente à qual a propriedade está associada e o tipo da propriedade.

PropertyDescriptor fornece as seguintes propriedades e métodos:

• Converter contém o TypeConverter dessa propriedade.

• IsLocalizable indica se essa propriedade deve ser localizada.

• GetEditor retorna um editor do tipo especificado.

PropertyDescriptor também fornece as seguintes propriedades e métodos de abstract:

• ComponentType contém o tipo de componente ao qual essa propriedade está associada.

• IsReadOnly indica se essa propriedade é somente leitura.

• PropertyType obtém o tipo da propriedade.

• CanResetValue indica se a redefinição do componente altera o valor do componente.

• GetValue retorna o valor atual da propriedade em um componente.

• ResetValue redefine o valor dessa propriedade do componente.

• SetValue define o valor do componente como um valor diferente.

• ShouldSerializeValue indica se o valor dessa propriedade precisa ser mantido.

Normalmente, os membros abstract são implementados por meio da reflexão. Para obter mais informações sobre reflexão, consulte os tópicos em Reflection.

Construtores

Propriedades

Métodos

Aplica-se a

Confira também

• MemberDescriptor
• Attribute
• DefaultValueAttribute