TypeDescriptionProvider.cs source code in C# .NET

                        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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TypeDescriptionProvider.cs source code in C# .NET

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