Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / CompMod / System / ComponentModel / TypeDescriptionProvider.cs / 1 / TypeDescriptionProvider.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- namespace System.ComponentModel { using System; using System.Collections; using System.Reflection; using System.Security.Permissions; ////// 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 /// [HostProtection(SharedState = true)] public abstract class TypeDescriptionProvider { private TypeDescriptionProvider _parent; private EmptyCustomTypeDescriptor _emptyDescriptor; ////// 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. /// protected TypeDescriptionProvider() { } ////// 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. /// protected TypeDescriptionProvider(TypeDescriptionProvider parent) { _parent = parent; } ////// 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. /// 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); } ////// 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. /// public virtual IDictionary GetCache(object instance) { if (_parent != null) { return _parent.GetCache(instance); } return null; } ////// 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. /// public virtual ICustomTypeDescriptor GetExtendedTypeDescriptor(object instance) { if (_parent != null) { return _parent.GetExtendedTypeDescriptor(instance); } if (_emptyDescriptor == null) { _emptyDescriptor = new EmptyCustomTypeDescriptor(); } return _emptyDescriptor; } ////// 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. /// public virtual string GetFullComponentName(object component) { if (_parent != null) { return _parent.GetFullComponentName(component); } return GetTypeDescriptor(component).GetComponentName(); } ////// 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. /// public Type GetReflectionType(Type objectType) { return GetReflectionType(objectType, null); } ////// 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. /// public Type GetReflectionType(object instance) { if (instance == null) { throw new ArgumentNullException("instance"); } return GetReflectionType(instance.GetType(), instance); } ////// 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. /// public virtual Type GetReflectionType(Type objectType, object instance) { if (_parent != null) { return _parent.GetReflectionType(objectType, instance); } return objectType; } ////// 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. /// public ICustomTypeDescriptor GetTypeDescriptor(Type objectType) { return GetTypeDescriptor(objectType, null); } ////// 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. /// public ICustomTypeDescriptor GetTypeDescriptor(object instance) { if (instance == null) { throw new ArgumentNullException("instance"); } return GetTypeDescriptor(instance.GetType(), instance); } ////// 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. /// public virtual ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance) { if (_parent != null) { return _parent.GetTypeDescriptor(objectType, instance); } if (_emptyDescriptor == null) { _emptyDescriptor = new EmptyCustomTypeDescriptor(); } return _emptyDescriptor; } ////// A simple empty descriptor that is used as a placeholder for times /// when the user does not provide their own. /// private sealed class EmptyCustomTypeDescriptor : CustomTypeDescriptor { } } }
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