PropertyDescriptor Klas

Definitie

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

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

public abstract class PropertyDescriptor : System.ComponentModel.MemberDescriptor

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

type PropertyDescriptor = class
    inherit MemberDescriptor

Public MustInherit Class PropertyDescriptor
Inherits MemberDescriptor

Overname

Object

MemberDescriptor

PropertyDescriptor

Afgeleid

System.ComponentModel.DependencyPropertyDescriptor

System.ComponentModel.TypeConverter.SimplePropertyDescriptor

Kenmerken

ComVisibleAttribute

Voorbeelden

Het volgende codevoorbeeld is gebaseerd op het voorbeeld in de PropertyDescriptorCollection klasse. Hiermee worden de gegevens (categorie, beschrijving, weergavenaam) van de tekst van een knop in een tekstvak afgedrukt. Hierbij wordt ervan uitgegaan dat button1 en textbox1 zijn geïnstantieerd op een formulier.

// 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.
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 & ControlChars.Cr
TextBox1.Text += myProperty.Description & ControlChars.Cr
TextBox1.Text += myProperty.Category & ControlChars.Cr

In het volgende codevoorbeeld ziet u hoe u een aangepaste eigenschapsdescriptor implementeert die een alleen-lezen wrapper rond een eigenschap biedt. De SerializeReadOnlyPropertyDescriptor eigenschap wordt gebruikt in een aangepaste ontwerpfunctie om een alleen-lezen eigenschapsdescriptor te bieden voor de eigenschap van Size het besturingselement.

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

namespace ReadOnlyPropertyDescriptorTest;

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

    public SerializeReadOnlyPropertyDescriptor(PropertyDescriptor pd)
        : base(pd) => _pd = pd;

    public override AttributeCollection Attributes => AppendAttributeCollection(
                _pd.Attributes,
                ReadOnlyAttribute.Yes);

    protected override void FillAttributes(IList attributeList) => attributeList.Add(ReadOnlyAttribute.Yes);

    public override Type ComponentType => _pd.ComponentType;

    // The type converter for this property.
    // A translator can overwrite with its own converter.
    public override TypeConverter Converter => _pd.Converter;

    // Returns the property editor 
    // A translator can overwrite with its own editor.
    public override object GetEditor(Type editorBaseType) => _pd.GetEditor(editorBaseType);

    // Specifies the property is read only.
    public override bool IsReadOnly => true;

    public override Type PropertyType => _pd.PropertyType;

    public override bool CanResetValue(object component) => _pd.CanResetValue(component);

    public override object GetValue(object component) => _pd.GetValue(component);

    public override void ResetValue(object component) => _pd.ResetValue(component);

    public override void SetValue(object component, object val) => _pd.SetValue(component, val);

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

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

        return result;
    }

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

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

        newAttrs ??= [];

        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(nameof(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

In de volgende codevoorbeelden ziet u hoe u de SerializeReadOnlyPropertyDescriptor functie gebruikt in een aangepaste ontwerpfunctie.

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(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.Windows.Forms

<Designer(GetType(DemoControlDesigner))>
Public Class DemoControl
    Inherits Control

    Public Sub New()

    End Sub
End Class

Opmerkingen

Een beschrijving van een eigenschap bestaat uit een naam, de kenmerken ervan, de onderdeelklasse waaraan de eigenschap is gekoppeld en het type eigenschap.

PropertyDescriptor biedt de volgende eigenschappen en methoden:

• Converter bevat de TypeConverter eigenschap voor deze eigenschap.

• IsLocalizable geeft aan of deze eigenschap moet worden gelokaliseerd.

• GetEditor retourneert een editor van het opgegeven type.

PropertyDescriptor biedt ook de volgende abstract eigenschappen en methoden:

• ComponentType bevat het type onderdeel waaraan deze eigenschap is gebonden.

• IsReadOnly geeft aan of deze eigenschap het kenmerk Alleen-lezen heeft.

• PropertyType haalt het type eigenschap op.

• CanResetValue geeft aan of het opnieuw instellen van het onderdeel de waarde van het onderdeel wijzigt.

• GetValue retourneert de huidige waarde van de eigenschap voor een onderdeel.

• ResetValue stelt de waarde voor deze eigenschap van het onderdeel opnieuw in.

• SetValue stelt de waarde van het onderdeel in op een andere waarde.

• ShouldSerializeValue geeft aan of de waarde van deze eigenschap moet worden behouden.

Normaal gesproken worden de abstract leden geïmplementeerd via reflectie. Zie de onderwerpen in Weerspiegeling voor meer informatie over reflectie.

Zie ook

• MemberDescriptor
• Attribute
• DefaultValueAttribute