ComEventsMethod.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / Runtime / InteropServices / ComEventsMethod.cs / 1305376 / ComEventsMethod.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 

/*============================================================ 
** 
** Class:  ComEventsMethod
** 
** Purpose: part of ComEventHelpers APIs which allow binding
** managed delegates to COM's connection point based events.
**
** Date:  April 2008 
**/
 
using System; 
using System.Collections.Generic;
using System.Text; 
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Reflection;
 
#if FEATURE_COMINTEROP
 
namespace System.Runtime.InteropServices { 

    // see code:ComEventsHelper#ComEventsArchitecture 
    internal class ComEventsMethod {

        // This delegate wrapper class handles dynamic invocation of delegates. The reason for the wrapper's
        // existence is that under certain circumstances we need to coerce arguments to types expected by the 
        // delegates signature. Normally, reflection (Delegate.DynamicInvoke) handles types coercion
        // correctly but one known case is when the expected signature is 'ref Enum' - in this case 
        // reflection by design does not do the coercion. Since we need to be compatible with COM interop 
        // handling of this scenario - we are pre-processing delegate's signature by looking for 'ref enums'
        // and cache the types required for such coercion. 
        internal class DelegateWrapper {
            private Delegate _d;

            private bool _once = false; 
            private int _expectedParamsCount;
            private Type[] _cachedTargetTypes; 
 
            public DelegateWrapper(Delegate d) {
                _d = d; 
            }

            public Delegate Delegate {
                get { return _d; } 
                set { _d = value; }
            } 
 
            public object Invoke(object[] args) {
                if (_d == null) 
                    return null;

                if (_once == false) {
                    PreProcessSignature(); 
                    _once = true;
                } 
 
                if (_cachedTargetTypes != null && _expectedParamsCount == args.Length) {
                    for (int i = 0; i < _expectedParamsCount; i++) { 
                        if (_cachedTargetTypes[i] != null) {
                            args[i] = Enum.ToObject(_cachedTargetTypes[i], args[i]);
                        }
                    } 
                }
 
                return _d.DynamicInvoke(args); 
            }
 
            private void PreProcessSignature() {
                ParameterInfo[] parameters = _d.Method.GetParameters();
                _expectedParamsCount = parameters.Length;
 
                Type[] enumTypes = new Type[_expectedParamsCount];
 
                bool needToHandleCoercion = false; 

                for (int i = 0; i < _expectedParamsCount; i++) { 
                    ParameterInfo pi = parameters[i];
                    // recognize only 'ref Enum' signatures and cache
                    // both enum type and the underlying type.
                    if (pi.ParameterType.IsByRef && 
                        pi.ParameterType.HasElementType &&
                        pi.ParameterType.GetElementType().IsEnum) { 
 
                        needToHandleCoercion = true;
                        enumTypes[i] = pi.ParameterType.GetElementType(); 
                    }
                }

                if (needToHandleCoercion == true) { 
                    _cachedTargetTypes = enumTypes;
                } 
            } 
        }
 
        #region private fields

        /// 
        /// Invoking ComEventsMethod means invoking a multi-cast delegate attached to it. 
        /// Since multicast delegate's built-in chaining supports only chaining instances of the same type,
        /// we need to complement this design by using an explicit linked list data structure. 
        ///  
        private DelegateWrapper [] _delegateWrappers;
 
        private int _dispid;
        private ComEventsMethod _next;

        #endregion 

 
        #region ctor 

        internal ComEventsMethod(int dispid) { 
            _delegateWrappers = null;
            _dispid = dispid;
        }
 
        #endregion
 
 
        #region static internal methods
 
        internal static ComEventsMethod Find(ComEventsMethod methods, int dispid) {
            while (methods != null && methods._dispid != dispid) {
                methods = methods._next;
            } 
            return methods;
        } 
 
        internal static ComEventsMethod Add(ComEventsMethod methods, ComEventsMethod method) {
            method._next = methods; 
            return method;
        }

        internal static ComEventsMethod Remove(ComEventsMethod methods, ComEventsMethod method) { 
            if (methods == method) {
                methods = methods._next; 
            } else { 
                ComEventsMethod current = methods;
                while (current != null && current._next != method) 
                    current = current._next;
                if (current != null)
                    current._next = method._next;
            } 

            return methods; 
        } 

        #endregion 


        #region public properties / methods
 
        internal int DispId {
            get { return _dispid; } 
        } 

        internal bool Empty { 
            get { return _delegateWrappers == null || _delegateWrappers.Length == 0; }
        }

        internal void AddDelegate(Delegate d) { 
            int count = 0;
            if (_delegateWrappers != null) { 
                count = _delegateWrappers.Length; 
            }
 
            for (int i = 0; i < count; i++) {
                if (_delegateWrappers[i].Delegate.GetType() == d.GetType()) {
                    _delegateWrappers[i].Delegate = Delegate.Combine(_delegateWrappers[i].Delegate, d);
                    return; 
                }
            } 
 
            DelegateWrapper [] newDelegateWrappers = new DelegateWrapper[count + 1];
            if (count > 0) { 
                _delegateWrappers.CopyTo(newDelegateWrappers, 0);
            }

            DelegateWrapper wrapper = new DelegateWrapper(d); 
            newDelegateWrappers[count] = wrapper;
 
            _delegateWrappers = newDelegateWrappers; 
        }
 
        internal void RemoveDelegate(Delegate d) {

            int count = _delegateWrappers.Length;
            int removeIdx = -1; 

            for (int i = 0; i < count; i++) { 
                if (_delegateWrappers[i].Delegate.GetType() == d.GetType()) { 
                    removeIdx = i;
                    break; 
                }
            }

            if (removeIdx < 0) 
                return;
 
            Delegate newDelegate = Delegate.Remove(_delegateWrappers[removeIdx].Delegate, d); 
            if (newDelegate != null) {
                _delegateWrappers[removeIdx].Delegate = newDelegate; 
                return;
            }

            // now remove the found entry from the _delegates array 

            if (count == 1) { 
                _delegateWrappers = null; 
                return;
            } 

            DelegateWrapper [] newDelegateWrappers = new DelegateWrapper[count - 1];
            int j = 0;
            while (j < removeIdx) { 
                newDelegateWrappers[j] = _delegateWrappers[j];
                j++; 
            } 
            while (j < count-1) {
                newDelegateWrappers[j] = _delegateWrappers[j + 1]; 
                j++;
            }

            _delegateWrappers = newDelegateWrappers; 
        }
 
        internal object Invoke(object[] args) { 
            BCLDebug.Assert(Empty == false, "event sink is executed but delegates list is empty");
 
            // Issue: see code:ComEventsHelper#ComEventsRetValIssue
            object result = null;
            DelegateWrapper[] invocationList = _delegateWrappers;
            foreach (DelegateWrapper wrapper in invocationList) { 
                if (wrapper == null || wrapper.Delegate == null)
                    continue; 
 
                result = wrapper.Invoke(args);
            } 

            return result;
        }
 
        #endregion
    } 
} 

#endif 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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ComEventsMethod.cs source code in C# .NET

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