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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.Contracts;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
namespace System.Runtime.InteropServices.WindowsRuntime
{
// This is a set of stub methods implementing the support for the IIterable`1 interface on managed
// objects that implement IEnumerable`1. Used by the interop mashaling infrastructure.
//
// The methods on this class must be written VERY carefully to avoid introducing security holes.
// That's because they are invoked with special "this"! The "this" object
// for all of these methods are not EnumerableToIterableAdapter objects. Rather, they are of type
// IEnumerable<T>. No actual EnumerableToIterableAdapter object is ever instantiated. Thus, you will
// see a lot of expressions that cast "this" to "IEnumerable<T>".
internal sealed class EnumerableToIterableAdapter
{
private EnumerableToIterableAdapter()
{
Debug.Assert(false, "This class is never instantiated");
}
// This method is invoked when First is called on a managed implementation of IIterable<T>.
internal IIterator<T> First_Stub<T>()
{
IEnumerable<T> _this = JitHelpers.UnsafeCast<IEnumerable<T>>(this);
return new EnumeratorToIteratorAdapter<T>(_this.GetEnumerator());
}
}
internal sealed class EnumerableToBindableIterableAdapter
{
private EnumerableToBindableIterableAdapter()
{
Debug.Assert(false, "This class is never instantiated");
}
internal sealed class NonGenericToGenericEnumerator : IEnumerator<object>
{
private IEnumerator enumerator;
public NonGenericToGenericEnumerator(IEnumerator enumerator)
{ this.enumerator = enumerator; }
public object Current { get { return enumerator.Current; } }
public bool MoveNext() { return enumerator.MoveNext(); }
public void Reset() { enumerator.Reset(); }
public void Dispose() { }
}
// This method is invoked when First is called on a managed implementation of IBindableIterable.
internal IBindableIterator First_Stub()
{
IEnumerable _this = JitHelpers.UnsafeCast<IEnumerable>(this);
return new EnumeratorToIteratorAdapter<object>(new NonGenericToGenericEnumerator(_this.GetEnumerator()) );
}
}
// Adapter class which holds a managed IEnumerator<T>, exposing it as a Windows Runtime IIterator<T>
internal sealed class EnumeratorToIteratorAdapter<T> : IIterator<T>, IBindableIterator
{
private IEnumerator<T> m_enumerator;
private bool m_firstItem = true;
private bool m_hasCurrent;
internal EnumeratorToIteratorAdapter(IEnumerator<T> enumerator)
{
Contract.Requires(enumerator != null);
m_enumerator = enumerator;
}
public T Current
{
get
{
// IEnumerator starts at item -1, while IIterators start at item 0. Therefore, if this is the
// first access to the iterator we need to advance to the first item.
if (m_firstItem)
{
m_firstItem = false;
MoveNext();
}
if (!m_hasCurrent)
{
throw WindowsRuntimeMarshal.GetExceptionForHR(__HResults.E_BOUNDS, null);
}
return m_enumerator.Current;
}
}
object IBindableIterator.Current
{
get
{
return (object)((IIterator<T>)this).Current;
}
}
public bool HasCurrent
{
get
{
// IEnumerator starts at item -1, while IIterators start at item 0. Therefore, if this is the
// first access to the iterator we need to advance to the first item.
if (m_firstItem)
{
m_firstItem = false;
MoveNext();
}
return m_hasCurrent;
}
}
public bool MoveNext()
{
try
{
m_hasCurrent = m_enumerator.MoveNext();
}
catch (InvalidOperationException e)
{
throw WindowsRuntimeMarshal.GetExceptionForHR(__HResults.E_CHANGED_STATE, e);
}
return m_hasCurrent;
}
public int GetMany(T[] items)
{
if (items == null)
{
return 0;
}
int index = 0;
while (index < items.Length && HasCurrent)
{
items[index] = Current;
MoveNext();
++index;
}
if (typeof(T) == typeof(string))
{
string[] stringItems = items as string[];
// Fill the rest of the array with String.Empty to avoid marshaling failure
for (int i = index; i < items.Length; ++i)
stringItems[i] = String.Empty;
}
return index;
}
}
}
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