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//------------------------------------------------------------------------------
// <copyright file="TypeDescriptionProvider.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.ComponentModel {
using System;
using System.Collections;
using System.Reflection;
using System.Security.Permissions;
/// <devdoc>
/// The TypeDescriptionProvider class can be thought of as a "plug-in" for
/// TypeDescriptor. There can be multiple type description provider classes
/// all offering metadata to TypeDescriptor
/// </devdoc>
[HostProtection(SharedState = true)]
public abstract class TypeDescriptionProvider
{
private TypeDescriptionProvider _parent;
private EmptyCustomTypeDescriptor _emptyDescriptor;
/// <devdoc>
/// There are two versions of the constructor for this class. The empty
/// constructor is identical to using TypeDescriptionProvider(null).
/// If a child type description provider is passed into the constructor,
/// the "base" versions of all methods will call to this parent provider.
/// If no such provider is given, the base versions of the methods will
/// return empty, but valid values.
/// </devdoc>
protected TypeDescriptionProvider()
{
}
/// <devdoc>
/// There are two versions of the constructor for this class. The empty
/// constructor is identical to using TypeDescriptionProvider(null).
/// If a child type description provider is passed into the constructor,
/// the "base" versions of all methods will call to this parent provider.
/// If no such provider is given, the base versions of the methods will
/// return empty, but valid values.
/// </devdoc>
protected TypeDescriptionProvider(TypeDescriptionProvider parent)
{
_parent = parent;
}
/// <devdoc>
/// This method is used to create an instance that can substitute for another
/// data type. If the method is not interested in providing a substitute
/// instance, it should call base.
///
/// This method is prototyped as virtual, and by default returns null if no
/// parent provider was passed. If a parent provider was passed, this
/// method will invoke the parent provider's CreateInstance method.
/// </devdoc>
public virtual object CreateInstance(IServiceProvider provider, Type objectType, Type[] argTypes, object[] args)
{
if (_parent != null)
{
return _parent.CreateInstance(provider, objectType, argTypes, args);
}
if (objectType == null) {
throw new ArgumentNullException("objectType");
}
return SecurityUtils.SecureCreateInstance(objectType, args);
}
/// <devdoc>
/// TypeDescriptor may need to perform complex operations on collections of metadata.
/// Since types are not unloaded for the life of a domain, TypeDescriptor will
/// automatically cache the results of these operations based on type. There are a
/// number of operations that use live object instances, however. These operations
/// cannot be cached within TypeDescriptor because caching them would prevent the
/// object from garbage collecting. Instead, TypeDescriptor allows for a per-object
/// cache, accessed as an IDictionary of key/value pairs, to exist on an object.
/// The GetCache method returns an instance of this cache. GetCache will return
/// null if there is no supported cache for an object.
/// </devdoc>
public virtual IDictionary GetCache(object instance)
{
if (_parent != null)
{
return _parent.GetCache(instance);
}
return null;
}
/// <devdoc>
/// This method returns an extended custom type descriptor for the given object.
/// An extended type descriptor is a custom type descriptor that offers properties
/// that other objects have added to this object, but are not actually defined on
/// the object. For example, in the .NET Framework Component Model, objects that
/// implement the interface IExtenderProvider can "attach" properties to other
/// objects that reside in the same logical container. The GetTypeDescriptor
/// method does not return a type descriptor that provides these extra extended
/// properties. GetExtendedTypeDescriptor returns the set of these extended
/// properties. TypeDescriptor will automatically merge the results of these
/// two property collections. Note that while the .NET Framework component
/// model only supports extended properties this API can be used for extended
/// attributes and events as well, if the type description provider supports it.
/// </devdoc>
public virtual ICustomTypeDescriptor GetExtendedTypeDescriptor(object instance)
{
if (_parent != null)
{
return _parent.GetExtendedTypeDescriptor(instance);
}
if (_emptyDescriptor == null) {
_emptyDescriptor = new EmptyCustomTypeDescriptor();
}
return _emptyDescriptor;
}
protected internal virtual IExtenderProvider[] GetExtenderProviders(object instance)
{
if (_parent != null)
{
return _parent.GetExtenderProviders(instance);
}
if (instance == null)
{
throw new ArgumentNullException("instance");
}
return new IExtenderProvider[0];
}
/// <devdoc>
/// The name of the specified component, or null if the component has no name.
/// In many cases this will return the same value as GetComponentName. If the
/// component resides in a nested container or has other nested semantics, it may
/// return a different fully qualfied name.
///
/// If not overridden, the default implementation of this method will call
/// GetTypeDescriptor.GetComponentName.
/// </devdoc>
public virtual string GetFullComponentName(object component) {
if (_parent != null) {
return _parent.GetFullComponentName(component);
}
return GetTypeDescriptor(component).GetComponentName();
}
/// <devdoc>
/// The GetReflection method is a lower level version of GetTypeDescriptor.
/// If no custom type descriptor can be located for an object, GetReflectionType
/// is called to perform normal reflection against the object.
/// </devdoc>
public Type GetReflectionType(Type objectType)
{
return GetReflectionType(objectType, null);
}
/// <devdoc>
/// The GetReflection method is a lower level version of GetTypeDescriptor.
/// If no custom type descriptor can be located for an object, GetReflectionType
/// is called to perform normal reflection against the object.
///
/// This method is prototyped as virtual, and by default returns the
/// object type if no parent provider was passed. If a parent provider was passed, this
/// method will invoke the parent provider's GetReflectionType method.
/// </devdoc>
public Type GetReflectionType(object instance)
{
if (instance == null)
{
throw new ArgumentNullException("instance");
}
return GetReflectionType(instance.GetType(), instance);
}
/// <devdoc>
/// The GetReflection method is a lower level version of GetTypeDescriptor.
/// If no custom type descriptor can be located for an object, GetReflectionType
/// is called to perform normal reflection against the object.
///
/// This method is prototyped as virtual, and by default returns the
/// object type if no parent provider was passed. If a parent provider was passed, this
/// method will invoke the parent provider's GetReflectionType method.
/// </devdoc>
public virtual Type GetReflectionType(Type objectType, object instance)
{
if (_parent != null)
{
return _parent.GetReflectionType(objectType, instance);
}
return objectType;
}
/// <devdoc>
/// The GetRuntimeType method reverses GetReflectionType to convert a reflection type
/// back into a runtime type. Historically the Type.UnderlyingSystemType property has
/// been used to return the runtime type. This isn't exactly correct, but it needs
/// to be preserved unless all type description providers are revised.
/// </devdoc>
public virtual Type GetRuntimeType(Type reflectionType)
{
if (_parent != null)
{
return _parent.GetRuntimeType(reflectionType);
}
if (reflectionType == null)
{
throw new ArgumentNullException("reflectionType");
}
if (reflectionType.GetType().Assembly == typeof(object).Assembly)
{
return reflectionType;
}
return reflectionType.UnderlyingSystemType;
}
/// <devdoc>
/// This method returns a custom type descriptor for the given type / object.
/// The objectType parameter is always valid, but the instance parameter may
/// be null if no instance was passed to TypeDescriptor. The method should
/// return a custom type descriptor for the object. If the method is not
/// interested in providing type information for the object it should
/// return base.
/// </devdoc>
public ICustomTypeDescriptor GetTypeDescriptor(Type objectType)
{
return GetTypeDescriptor(objectType, null);
}
/// <devdoc>
/// This method returns a custom type descriptor for the given type / object.
/// The objectType parameter is always valid, but the instance parameter may
/// be null if no instance was passed to TypeDescriptor. The method should
/// return a custom type descriptor for the object. If the method is not
/// interested in providing type information for the object it should
/// return base.
/// </devdoc>
public ICustomTypeDescriptor GetTypeDescriptor(object instance)
{
if (instance == null)
{
throw new ArgumentNullException("instance");
}
return GetTypeDescriptor(instance.GetType(), instance);
}
/// <devdoc>
/// This method returns a custom type descriptor for the given type / object.
/// The objectType parameter is always valid, but the instance parameter may
/// be null if no instance was passed to TypeDescriptor. The method should
/// return a custom type descriptor for the object. If the method is not
/// interested in providing type information for the object it should
/// return base.
///
/// This method is prototyped as virtual, and by default returns a
/// custom type descriptor that returns empty collections for all values
/// if no parent provider was passed. If a parent provider was passed,
/// this method will invoke the parent provider's GetTypeDescriptor
/// method.
/// </devdoc>
public virtual ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
{
if (_parent != null)
{
return _parent.GetTypeDescriptor(objectType, instance);
}
if (_emptyDescriptor == null) {
_emptyDescriptor = new EmptyCustomTypeDescriptor();
}
return _emptyDescriptor;
}
/// <devdoc>
/// This method returns true if the type is "supported" by the type descriptor
/// and its chain of type description providers.
/// </devdoc>
public virtual bool IsSupportedType(Type type)
{
if (type == null)
{
throw new ArgumentNullException("type");
}
if (_parent != null)
{
return _parent.IsSupportedType(type);
}
return true;
}
/// <devdoc>
/// A simple empty descriptor that is used as a placeholder for times
/// when the user does not provide their own.
/// </devdoc>
private sealed class EmptyCustomTypeDescriptor : CustomTypeDescriptor {
}
}
}
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